a study of some californian indian rock art pigments; david a. scott and william d. hyder

A Study of Some Californian Indian Rock Art PigmentsAuthor(s): David A. Scott and William D. HyderReviewed work(s):Source: Studies in Conservation, Vol. 38, No. 3 (Aug., 1993), pp. 155-173Published by: International Institute for Conservation of Historic and Artistic WorksStable URL: http://www.jstor.org/stable/1506377 .Accessed: 17/02/2012 14:03

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A STUDY OF SOME CALIFORNIAN INDIAN ROCK ART PIGMENTS

David A. Scott and William D. Hyder

Abstract-A study was made of a number of rock art sites in California to determine which pigments had been used by the Chumash Indians. The study was based on pigment microsamples and rock art fragments excavated from site debris. The techniques of examination employed in the study were polarized light microscopy, environmental scanning electron microscopy, electron microprobe analysis, colour recording on site and X-ray powder diffraction. The pigments identified by this study include yellow ochre, red ochre, wood charcoal, halloysite (a white clay) and a white which is probably shell white. The mineral crusts associated with the rock art surface were also studied and gypsum was found to be a common component, together with the calcium oxalate, whewellite. The potential alteration of carbonate pigments to gypsum is inferred from the study. The paper is illustrated with examples of deteriorated rock art and with cross-sections from the sites discussed, particularly Carneros Rock and Painted Rock.

1 Introduction

Many different Indian cultures have inhabited the Californian area, of whom the best known are the Chumash Indians. The Chumash inhabited the south central coastal zone of California for over a thousand years. They were skilled craftsmen who lived in settled communities of small villages and who obtained materials and food from the abun- dant marine and terrestrial resources of the area. Craft specialization among the Chumash resulted in the production of plank canoes, shell currency, stone bowls and mortars and fine basketry, as well as flint-working, the uti- lization of a wide variety of plants and some notable rock art [1]. Ethnographic information suggests that Chumash art which particularly associated with a religious or shamanistic cult known as the 'antap which occupied a powerful position in Chumash society. Many

Received 26 May 1992

Studies in Conservation 38 (1993) 155-173

Chumash rituals were related to astronomical or astrological observations and the Chumash carefully observed the phases of the moon and the setting and declination of the sun [2]; these celestial observations may also have influenced rock art location or design.

Most of the rock art sites occur on sandstone outcrops in the foothills or mountain regions of southern California's traverse mountain ranges, in an area slightly greater than Santa Barbara County and Ventura County. The art often takes the form of detailed polychrome paintings, especially man- dalas or ornate circular motifs [3]. Other common elements include insects and lizard-like creatures and occasional representational motifs. The art is usually small-scale and fre- quently framed in natural rock cavities or hol- lows; most is associated with or in close proximity to other archaeological features [4]. Hyder has categorized Chumash rock art in three principal groups: line drawings applied to the bare rock, monochrome paintings and polychrome paintings [4]. The colours used to make this rock art were red, black, white, yellow, blue and green. Blue and green are quite rare and were not found in any of the sites discussed in this paper. Empirical observation suggests that red pigments have survived bet- ter than white and black. Most archaeologists accept that ochre or haematite was used for the red, but there is some question as to the identity of the black, white and other pigments employed by the Chumash.

The first reports of the existence of rock art in the region date from the 1880s [5], while the recording and examination of the sites themselves were spurred by the publication of a seminal study by Campbell Grant in 1965 [6]. Detailed scientific study of aboriginal colorants and the determination of the age of rock art pigments by accelerator mass- spectrometry radiocarbon dating have recently been the subject of several papers [7-12], but

155


little scientific work has been published relating to pictograph sites in California. The analysis of pigments is central to the study of rock art, yet sampling of pictographs is often problematic due to their fragility and the damage that can be caused to the surface by removal of pigment. This paper describes work on pigment identification and the nature of the deposits on the surface of the pictographs, both of which are important for conservation studies and for monitoring of the sites. Most of the work reported in this paper was carried out on rock art fragments which had become detached from the sites and were found lying in debris. Where pigment studies could be undertaken, additional examination was carried out on pigment microsamples removed with a tungsten needle and micro- scalpel, with the permission of the relevant authorities.

Techniques used to study the pigment samples include polarized light microscopy on microsamples, Debye-Scherrer X-ray powder diffraction, transmitted and reflected light microscopy, electron microprobe analysis, and colour recording with a portable Minolta CR121 Chromameter.

2 Ethnographic information concerning pigments

The extensive field notes recorded by the ethnographer J.P. Harrington in over 30 years of work in the area form an important archive for research into the Chumash and other Californian Indian groups. A thorough survey of the literature relating to the culture of the Chumash is provided by the multi-volume work of Hudson and Blackburn [13] and numerous research papers by Harrington him- self [14]. In the Chumash area, after mining or preparation of the pigment, it was often made into small loaves or cakes, probably by mixing with a binder. The cakes could then be easily transported or traded. Pigment could be applied with brushes made from yucca, soap- root or duck feathers as well as by finger- painting. Small stone mortars and pestles may have been used to grind the pigment cakes before application. These pigment cakes were often contained in hollowed-out pine cones, buckskin sacks, shells or baskets for storage and transport. 156

2.1 Red and yellow pigments Red ochre and yellow ochre are very common rock art pigments. Australian rock art studies have suggested that selected ochre deposits were considered to be particularly powerful and ochre cakes prepared at specific quarries were traded over much of the continent, even when local deposits were available [15]. Red ochre deposits are widespread in the California area and small lumps of ochre can be picked up today from the soil and sand surrounding the site of Painted Rock, for example. Red ochre pigments were often spe- cially prepared and have been found in the form of carefully shaped cakes, stored in shell containers (Figure 1). One such cake in the

Figure 1 Shell container and red ochre from the Canalino cultural area, Santa Barbara County (Santa Barbara Museum of Natural History, NA- CA-123-4D-1, no. SP.1772 TA 933).

collection of the Santa Barbara Museum of Natural History has an incised design and is from an inland Chumash site. Heizer and Treganza record some interesting details of the preparation of red pigments by the Cocopa Indians from the area of Imperial County, on the border between Mexico and the United States [16]. The haematite used was a dull reddish colour, and to make the pigment brighter the Cocopa fired the mineral in situ. The roasted mineral was then removed in chunks and leached in water to remove salts and soften the lumps into a pasty mass. Harrington notes that springs could also


A study of some Californian Indian rock art pigments

provide haematite: in the summer months a reddish-brown scum, consisting mostly of the bacterium Leptothrix ochracea, which precipi- tates iron (III) hydroxide, appears on the surface of water in which hydrated iron oxides occur [17]. The red scum was collected by the Indians of the San Diego region, dried in the sun, and then burnt by placing it on a slab of bark from the tree Quercus kelloggii Newb. or some other suitable oak. Generally, temperatures in the range of 175-275?C are necessary to effect the breakdown of the iron oxyhydroxides such as goethite, a-FeOOH, to haematite, a-Fe203 [18-20]. Cook et al. found that this change can also occur by the dehy- dration of fine-grained goethite to haematite at temperatures as low as 40?C [10]. This has led to the suggestion that several Australian rock art sites which were originally painted in yellow ochre may have turned red over time through exposure to severe summer temperatures. Mined ochre deposits, which usually consist of a mixture of iron oxides and oxyhydroxides, could be turned a darker red on roasting by conversion of some of the oxyhydroxides to haematite.

The Indian groups differentiated between various red ochres; for example, the iron (III) hydroxide scum was called moo'ic while ordi- nary red haematite was navyot but the red made by burning the scum was called paa'isval. Red ashes or earth from the fire- place were teelinic qwayaqyac, while if the colour was of a pinkish hue it was teelinic 'av'axunt or teelinic 'ava'vac. Red clay for ground painting was to'xat qwayaqyac. Harrington was also informed that ochres var- ied in shade from orange-brown to scarlet and were traded to the Chumash Indians from Tulare County and from Santa Rosa Island. This ethnographic information is confirmed by site examination of ochres used by the Chumash: the colour range is from orange to scarlet. Hilhil was a name for red ochre and ilil was a red paint used for body painting. The Mojave Indians brought a bright red ilil while ohat was a red ochre obtained from the Yuma and Mohave Indians.

2.2 Black pigment Harrington's ethnographic data identify charcoal as the most common source of black [16:


items 445 and 448], although Grant reports that a fragment of black pigment found near Santa Barbara was identified as hydrous manganese oxide [6]. Some details regarding one method of preparing black pigments are given by Harrington [17]. Pinon twigs were broken up and fired in a soot collector. The soot, timuat, was collected on a roof made of rock slabs. The soot was scraped and then made into a dough with deer bone marrow. The resulting pigment was called osranihwat and was described as very black. Other informants mention ash-tree and oak bark as providing the best charcoal, called waqsik 'alcosoy. It could be ground and mixed with water. Another black was tuhut, which was not as black as osranihwat; the resulting pigment had a bluish tone and was called monusmu, traded by the Yumas and Mohaves.

2.3 White pigment White pigments have been variously described as diatomaceous earth, kaolin or burnt shell [16: item 445]. Grant [6] states that white was produced from diatomaceous earth from sources near Lompoc, while Harrington suggests that white kaolin was used [17]. Harring- ton's informants also record the use of burnt shell. Singer suggests that burnt shales could have been used as a source of pigments of a wide variety of hues, including white [21].

2.4 Blue and green pigments Lee identifies a blue-green pigment as probably being contemporary with pigments used during the establishment of the Spanish Missions to California [22]. Other possible sources include the mineral fuchsite, a variety of muscovite in which chromium replaces some of the aluminium in the lattice, which has been found in archaeological sites. There is very little information available concerning these pigments.

2.5 Binding media It has proved difficult to identify binding media from rock art sites. This has led to doubts about the use of binding media in pictograph painting, although this attitude is beginning to change as organic components are now being identified. For example, human blood residues have been identified in late

157

Pleistocene art from Australia [11]. Ethno- graphic information from California records that the Gabrielino and Luiseno Indians used oil from chilacayote plants, Marah macrocar- pus, the wild cucumber [23], but no organic binders from Californian pictograph samples have been identified at the time of writing. This is not to say that they have not been used; indeed, their use is probable.

3 The rock art sites

3.1 Present condition Apart from some site management and pro- tection, there has been very little conservation work undertaken on Chumash Indian rock art sites. The notable exception is the Painted Rock Conservation Training Program initiat- ed by the Getty Conservation Institute under the direction of Andrew Thorn. Vandalism and lack of appropriate treatment have resulted in a situation where continual loss of the rock art can be expected. Some of the principal factors affecting the art are: (a) Surface exfoliation. Loss of the surface

is accompanied by flaking or detach- ment, typically to a depth of 3-5mm. The loss of this surface crust is responsible for a great deal of damage to the sites. Surface exfoliation may be due to chemical, physical or biological factors. No simple mechanism can therefore be assumed in the absence of extensive research.

(b) Deposition of surface salts. These derive either from groundwater, by dissolution of rock components, or from chemical or biological interaction with the rock. Some surface deposits result in the rock art becoming obscured.

(c) Loss of the surface due to erosion, for instance by wind, rain or sand scouring. Some very exposed sites are gradually becoming very faint and it is increasingly difficult to see the images compared with examination in the recent past.

(d) Gunshot damage. Sites which are easily accessible are particularly prone to use as targets for firing practice, resulting in spalling and loss.

(e) Incised graffiti. These are cut into the top surface, removing original pigment.

158


(f) Applied graffiti. These sometimes outline the original art. For example, at the Painted Rock site, outlining with chalk has been used to aid photography.

(g) Modern painted graffiti. The application to the surface of house and spray paints, some of which are difficult to remove from the art.

(h) Smoke damage. Caused by the lighting of wood fires in the rock shelters.

(i) Biological agents. Lichen, fungi, plants and wildlife may all affect the site and the state of preservation of the rock art.

3.2 Some of the sites and pigment cakes examined The pigment study has been greatly facilitated by the availability of pictograph fragments from a number of sites visited by Georgia Lee and William Hyder over the past decade. These are not random samples but, rather, opportune collections made at sites which had already suffered deterioration and exfoliation of the surface, which justified the time taken in searching for small detached fragments. Pictograph fragments were studied from Californian sites in Santa Barbara County: Painted Cave (SBa-506), Morris Cabin Creek (SBa-1288), Pool Rock (SBa-1632) and Condor Cave (SBa-1633); in Kern County: Carneros Rock (Ker-161); in San Luis Obispo County in the area of Carrizo Plains: Edgar Rock (SLO-336), North Selby (SLO-1103, formerly SLO-995B) and Painted Rock (SLO- 79). In addition, pigment samples collected by David Whitley were kindly made available to the authors, from sites in Kern County located in Indian Wells Canyon (Ker-735 and Ker- 736). The approximate location of the sites studied is shown in Figure 2.

3.2.1. Painted Cave The site of Painted Cave, in Santa Barbara County, is located in a sandstone formation which is common to many of the other sites in this area. It is described as the Coldwater sandstone formation, a late Eocene marine deposit characterized by Dibblee as a hard, tan, bedded arkosic sandstone with minor interbeds of grey-green siltstone and shale [24]. This sandstone, although hard, weathers



Figure 2 Approximate location of some of the sites discussed, and historic ethnic boundaries in south central California. SBa-506: Painted Cave, SBa-1288: Morris Cabin Creek, SBa-1632: Pool Rock, SBa-1633: Condor Cave, Ker-161: Carneros Rock, Ker-735 and & Ker-736: Indian Wells Canyon, SLO-336: Edgar Rock, SLO-1103: North Selby, SLO-79: Painted Rock.

to become soft and friable, resulting in the exfoliation of the surface of the rock to a depth of about 3-5mm. The rock art images are complex and, although much vandalized, are some of the most impressive in the region. There are a number of different painting sequences at this site, the earliest being monochrome black line drawing. Superimposed are different geometric forms in red and complex polychrome paintings in red, black and white. In common with the other sites discussed here, except for those in Indian Wells Canyon, there is no assigned date for Painted Cave, although it is assumed that most of the art


was produced from about A.D. 500-1700. Pig- ment microsampling and colour recording were undertaken at this site.

3.2.2 Morris Cabin Creek Morris Cabin Creek is located in a dry cave, within a sloping face of Matilija sandstone. The art, which is polychrome, painted in red, black and white, is well protected inside a shelter about 12 metres square. Fragments of drawings were collected along the base of the shelter, attributable only to the general area of the east or west panels. Some of these fragments were mounted for light microscopy.

159

3.2.3 Pool Rock and Condor Cave Pool Rock and Condor Cave are located in a sandstone outcrop running along the base of Hurricane Deck in the Santa Barbara back- country. Neither site is a true cave, although they could be described as small shelters with associated middens.

The paintings of Condor Cave are well preserved in general, but a small panel at the east end of the shelter has nearly eroded away. Several small sandstone chips were collected from the sandy deposit at the base of the eroded panel. The Pool Rock paintings are in reasonable condition, although some areas of pigment adhere poorly to the rock and the surface is laced with microfractures. The paintings appear to have been darkened by campers' fires and the first evidence of vandalism appeared in 1990. Both are polychrome sites with paintings in red, black and white.

Microsamples for study of the white pigment and crust deposits were removed from the pigmented surfaces at Pool Rock.

Figure 3 Part of pictograph surface from the Carneros Rock site (Ker-161) in Kern County. Vandalism and loss of parts of the surface through exfoliation can be seen.

3.2.4 Carneros Rock The Carneros Rock site is located in the Vaqueros sandstone formation on the Central Valley side of the Temblor mountain range. The site lies within the historic Yokuts tribal area, although the art appears to be both Chumash and Yokuts in origin [25, 26]. The fragment discussed here was collected from the edge of what remains of a more extensive

160


polychrome panel located inside a badly wind- scoured shelter. Photographic documentation dating from 1925 indicates that most of the pictograph panel had already been lost at that time. Examination of the same panel in 1990 showed that considerable further deterioration had occurred as a result of erosion and exfoliation, although the pigmented surface survives well on the fragment recovered. Part of the damaged surface of the art is shown in Figure 3.

3.2.5 Painted Rock Painted Rock is the most important site in the Carrizo Plains area, situated in the Vaqueros sandstone formation described by Dibblee as a shallow marine, early Miocene deposit, mas- sive to thick-bedded and light greenish-grey to tan in colour with minor siltstone content and locally calcareous [24].

Painted Rock is a site of national historic significance in the opinion of Johnson, who dates the period of human occupation of the site from about 5000 to 7000 years B.P [27]. The association of the rock art with different Californian Indian groups and the lack of a precise date for the art do not necessarily mean that the site occupation was contempo- raneous with the art. The site has suffered from extensive exfoliation, vandalism and damage which can be seen from a comparison of the photographs shown in Grant [6] with documentation recorded by the Getty Conservation Institute in 1991 [28]. The damage includes incised graffiti, applied graffiti, gunshots and modern paint. Following conservation treatment by the team assembled by the Getty Conservation Institute, much of the gross damage to the site has been mitigated as far as possible. Small exfoliated fragments were available from this site and additional microsamples were taken for study of black overlying crusts and white deposits on the rock surface. Some colour recordings were also made.

Part of the damaged main polychrome panel is shown in Figure 4. The painted surface was outlined with chalk as an aid to photography some years ago, and it is now not possible to remove the chalk without potential damage to the art. The panel shown has suffered from extensive exfoliation and there are,


? . ..." ' . ..

1.

.....,...: ?L; . ?r?:? ::: (?? ?.?

P,Sf6ii"*

f '" '' 9L? '*1 " :? ?r.

I,,,,

I?'


4*

J-~ aCT~'d~ L~B~;IBTT il"l ^?B ffi^1 ' " " , "' 7

Figure 4 Part of a badly exfoliated rock art panel . . ::: :; from the Painted Rock site (SLO-79). Some of thei . elements have been recently outlined in chalk, an act u o' of vandalism used to aid photography.

Figure 5 Polished section of rock surface and ochre pigment from Carneros Rock (Ker-161), no. C22, . x 40. The section shows a sandstone matrix with d e

scattered charcoal and an evenly applied charcoal ' ;. layer under the red ochre.

I O

Figure 7 Polished thin-section under polarized light of a pigment surface from the North Selby site Figure 10 Thin-section of sample from Painted (SLO-1103, formerly SLO-995B), x 320. The sur- Rock under polarized light, x 400. Pink upper sur-

face crust consists of a thick gypsum layer which has face is mounting resin; white crystals are calcium entrapped the red ochre pigment particles, lifting oxalate monohydrate (whewellite) with some gyp- them from their original position. The gypsum sum; black layer is charcoal pigment; light blue is appears blue, oriented in laths, and a large ochre sandstone rock. Fibrous orange structure is organic particle is seen suspended. plant material within degraded rock surface.


4

161

Table 1 X-ray diffraction data for some pigments and mineral crusts from the rock art sites studied

Type of sample Site no. Name Location of sample Mineral species JCPDS number

pigment crust

green graffiti paint

black rock crust

black rock crust

white & black crust

red ochre cake

red ochre cake

red ochre cake

red ochre cake

red ochre pigment

red pigment panel #1

red pigment panel #2

crust material panel #6

dark red pigment

white pigment from shield

white pigment #3

white pigment

white pigment

SLO-79

SLO-79

SLO-79

SLO-79

SLO-79

NA-CA-125-13A-9

NA-CA-IA-12-1

156A-2835

SBa-1279-13A-

SLO-79

SLA-5235

SLA-5235

SLA-5235

SLA-5235

Ker-736

Ker-736

Tul-176

Ker-421

Painted Rock

Painted Rock

Painted Rock

Painted Rock

Painted Rock

Santa Cruz Island

Santa Barbara County

Santa Cruz Island

Sallisbury Potrero

Painted Rock

rock art site

rock art site

rock art site

rock art site

Indian Wells Canyon

Indian Wells Canyon

Fountain Spring

Indian Wells Canyon

excavated from immediate vicinity sample taken directly from rock surface sample taken directly from rock surface sample taken directly from rock surface sample taken directly from rock surface microsample taken from pigment cake microsample taken from pigment cake microsample taken from pigment cake microsample taken from pigment cake excavated from immediate vicinity microsample taken directly from site microsample taken directly from site microsample taken directly from site microsample taken directly from site microsample taken directly from site microsample taken directly from site microsample taken directly from site microsample taken directly from site

quartz, gypsum, whewellite gypsum (only species found) guanine

quartz, calcian albite, anorthite gypsum, guanine, whewellite haematite, quartz, calcian albite haematite, goethite, quartz haematite, anorthite gypsum, haematite quartz, haematite

haematite, whewellite, quartz quartz, bassanite, haematite barite, calcite, galena lepidocrocite, goethite, whewellite halloysite

halloysite

principally whewellite unidentified

33-1161; 33-311; 20-231

33-311

20-2012

33-1161; 9-457; 20-20

20-2012; 33-311; 20-231

33-1161; 9-457; 33-664

33-1161; 33-664; 29-713

9-465; 33-664

33-311; 33-664

33-161; 33-664

33-161; 20-231; 33-664

33-161; 33-664; 33-310

24-1035; 24-27; 5-592

8-98; 29-713; 20-231

9-451

9-451

20-2012

s

Fl

xO

--1 'o

-


in addition, some mineral crusts over part of the surface.

3.2.6 North Selby The North Selby site is also in the Carrizo Plains. It has suffered some deterioration and a section was taken from a fragment detached from panel 5 which was found in debris. The site was previously designated SLO-995B, but the reference has now been changed to SLO- 1103.

3.2.7 Indian Wells Canyon sites Pigment microsamples had been taken by Whitley from some sites in Indian Wells Canyon and these were made available to the authors for study. The Indian Wells Canyon sites are of interest since the pigments may have been obtained locally from Coso Hot Springs.

Samples of white pigment from two sites in Indian Wells Canyon, Kern County (Ker-735 and Ker-736), which had previously been examined by Whitley and Dorn [29], were available for study. These sites are examples of the Coso Painted Style, which includes white monochrome elements. The association of horse and rider elements indicates a date later than A.D. 1772 [30]. In the vicinity of these sites are the Coso Hot Springs which contain many sources of coloured mud and clay. It has been suggested that these were local sources of pigment for the rock art [31].

4 Results of the examination

4.1 Pigment cakes A number of pigment cakes in the collection of the Santa Barbara Museum of Natural History were studied. The cakes were examined by optical microscopy, X-ray fluorescence analysis and X-ray diffraction. Colour reflectance readings were taken with the Minolta CR121 Chromameter in the CIE LAB system. Optical microscopy of the cakes suggests that they were carefully prepared from ground red ochre. A pigment cake from Christies site, Santa Cruz Island, for example, has a particle size only four or five times larger than the best quality modern ochre pigments. The study showed that the cakes were Studies in Conservation 38 (1993) 155-173

of red or yellow ochre together with a number of mineral impurities. The range of impurities (by element only) found by non-destructive energy-dispersive X-ray fluorescence analysis encompassed copper, zinc, calcium, potassium, sulphur, phosphorus, manganese, chromium and silicon. Modern ochre samples, even pigments carefully prepared for painting conservation, show a very similar range of impurities. Red ochre deposits can typically be associated with ilmenite, rutile, feldspars, magnetite and calcite. The presence of titani- um and manganese in several Chumash samples suggests the presence of ilmenite (Fe, Mg, Mn)TiO3 as an impurity. X-ray diffraction showed quartz and haematite to be the most common components. A summary of some of the X-ray diffraction data from both pigments and crust deposits is given in Table 1.

Table 2 X-ray diffraction data for Chumash red ochre cake no. 2

I/I* d 33-1161 9-457 33-664 quartz calcian albite haematite

5 5

20 10 5

20 5

100 90 25

5 20 20 15 15 5

30 5

10 25 10 5 5 5

25 5

10 10

6.440 4-484 4-270 4.058 3-875 3-708 3.541 3.345 3-187 2.950 2-858 2-710 2.505 2-462 2-287 2.233 2-125 2-017 1.983 1.814 1.781 1.700 1-596 1.570 1.542 1.488 1-454 1.379

6.38/60

4.26/22 4.03/80 3-86/50 3-69/60 3-49/50

3-34/100 3-36/50 3.18/100 2.93/70 2-84/60

2-46/8 2-28/8 2-23/4 2-13/7

2.52/30 2-47/30

3-68/30

2-70/100 2-51/70

2-21/20

1-979/4 1-818/4

1-694/45 1-599/10

1-542/9

1-454/1 1-375/7

1-486/30 1-454/30

163


In a report on the pictograph pigments of Seminole Canyon in Val Verde County, Texas, Zolensky attempted to discriminate between the different iron oxides and oxyhydroxides by X-ray diffraction analysis of red and yellow pigments and to show by this means a chronological difference [32]. The practical value of such discrimination for Chumash sites is doubtful in view of the very diverse nature of ochre deposits, the preva- lence of the mineral in a number of different natural occurrences, and the changes which may have been caused by heating the pigment to alter the colour. X-ray diffraction for a sample of red ochre from Santa Cruz Island, from Coche Prietos (NA-CA-125-13A-9), found calcian albite, haematite and quartz. A sample from Santa Barbara County (NA-CA- 1A-12-1) gave quartz, haematite and goethite, while two further samples from Christies site, Santa Cruz Island, gave haematite and anorthite/albite. The presence in all the red ochre samples from Santa Cruz Island of albite or anorthite is possibly significant, but it would be difficult to trace these minerals in a ground pigment applied to the rock surface because of contamination and the complexity of the associated minerals.

4.2 Cross-sections Sections from some of the sites are illustrated. Figure 3 shows part of the rock art from the Carneros Rock site. A cross-section of a fragment from this site is shown in Figure 5, and illustrates good preservation of pigment layers over a quartz sandstone rock. The site of Carneros Rock has suffered extensive deterioration with the loss of much of the pictograph surface as a result of erosion, although the fragments collected show that some areas of the pigmented surface have not been badly disrupted. In fact, the pigmented surface has survived well in comparison to many of the fragments from the different sites studied. The section shown in Figure 5 was prepared by embedding a rock chip in epoxy resin. Following the removal of a thin slice for use as a thin-section, the remaining embedded fragment was finished using wet silicon car- bide papers from 200 to 600 grit. Final polish- ing was carried out to a lum diamond finish in lapping oil.

164

Figure 5 reveals a quartz sandstone rock covered with a mineral crust incorporating some fragments of charcoal. Overlying this layer can be seen a thin black layer of charcoal which is covered with a thick and very coherent layer of finely prepared red ochre. The contours of the charcoal layer below the ochre do not match the outline of the rock, so it is unsafe to conclude that the surface pigment layer has been lifted away from the rock surface, although this may indeed have occurred, causing distortion of the outer layer in the process. The complexity of the surface layers of many of these rock art sites is well illustrated by the environmental scanning electron micrograph shown in Figure 6. The advantage of using the environmental scanning electron microscope is that samples can be placed in the machine and examined in the uncoated state, allowing clear study of surface crusts and non-destructive sample preparation.

. ..... ... b...: : a

X { ,, I:

Figure 6 Environmental scanning electron microscope view (uncoated) of the surface of sample C21 from Carneros Rock. Scale bar: 20um. Intersecting plates of gypsum form a covering over the pigment surface.

In Figure 6 the same area of the surface is being studied as that shown in section in Figure 5. No pigment layer is visible on the surface; instead, a surface covering of interlocking gypsum crystals can be seen which it is not possible to observe with the naked eye. The growth of gypsum in the surface layers of the rock could either disrupt the painted sur-



face or it could act as a protective layer, pre- venting the continuing loss of the surface through erosion of the pigment. It is apparent that there is considerable variation in this process from site to site, as the section from the North Selby site illustrates (Figure 7). Here, an aggregate of red ochre particles is suspended in a thick matrix of gypsum plates which extend outward from the rock surface. The gypsum growth has caused severe disruption in the red ochre layer at this site, causing the ochre to be broken up and dislodged, in contrast to the Carneros Rock site where the ochre layer is well preserved.

Figure 8 Sample C21, Carneros Rock site (Ker- 161). Secondary electron image of charcoal fragment in black pigment layer. Structure is typical for wood charcoal. Scale bar: 10Oum. Most charcoal occurs as smallfragments 2-30/m in size.

In most of the sections studied, black is the first layer to be laid down in pictographs which contain red and black colorants. An area of the black colorant from the Carneros Rock site was examined by electron microprobe study and a secondary electron image of a charcoal fragment is shown in Figure 8. The charcoal is embedded in a mixed matrix of degraded rock minerals and gypsum. This study clearly shows fragments of the black colorants which display a woody structure, confirming that wood charcoal was used as the major black pigment of the Chumash. The samples examined from the Santa Barbara County area suggest that charcoal rather than


soot was commonly employed as a rock art pigment.

The existence of these quite thick charcoal pigment layers suggests that radiocarbon dates can be obtained from some sites by accelerator mass spectrometry of the carbon content, and this aspect of the work is currently under study. The site of Carneros Rock is so deteriorated that it was difficult to determine from visual examination whether the surface was blackened overall and the red paintings drawn on a charcoal ground, or whether the wall paintings were in red and black applied to the bare rock [33]. Examination of the Carneros Rock section illustrated in Figure 5 shows that the red paintings have been applied over a charcoal underlayer.

Study of the red pigments from the sites confirmed that they probably have similar ori- gins to the pigment cakes: all of them are red ochre with the most common components being haematite and quartz. Some of the X- ray diffraction data for the sites examined to date are shown in Table 1.

A study was made of the white pigments, particularly from sites in the Santa Barbara County area, by using mounted sections and pigment microsamples. Interestingly, the only component found in all of the white pigments was gypsum. The use of gypsum as a primary pigment in this area has never been suggested, nor is it probable. The original pigment was probably based on a shell white which has transformed to gypsum over time. No direct evidence for shell white could be found from the samples studied, since complete transformation had occurred: both polarized light microscopy and scanning electron microscopy revealed only gypsum. Shells are found in the vicinity of some of the sites, and the proximity of Santa Barbara County to the coast would make the use of shell white an obvious choice. White pigments from the sites of Pool Rock, Painted Cave, Morris Cabin Creek and Condor Cave all showed conversion to gypsum and some examples are listed in Table 1.

Gypsum crusts are commonly found on rock art sites from a wide variety of contexts. McKee and Thomas [8] report the identification of gypsum in pictographs at Toquima Cave, central Nevada, while North and Clarke [34] found gypsum deposition during their

165

jw %

David A. Scott and William D. Hvder

work on pigment identification in rock art from Kakadu National Park, Australia. Gypsum is slightly soluble in water, 0.241g being soluble in 100cc of cold water, while the solubility of calcium carbonate as calcite is only 0-0014g per 100cc of water. Gypsum is therefore some 2000 times more soluble than calcite in neutral water [35]. In damp conditions it will recrystallize and cycles of wetting and drying will enable larger crystals to grow from small aggregates. Chemical or biological factors may increase acidity at the rock surface, allowing further dissolution of any carbonate component. The morphology of the gypsum crystals which form at the surface is typically an interlocking mass of plates or smaller crystalline particles, projecting out- wards from the rock surface as shown in Figure 7.

It is well known that limestone buildings are covered with gypsum crusts as a result of sulphation and the same process of alteration, from a carbonate pigment to a sulphated product, was suggested by North and Clarke from their Kakadu work [34]. The alteration of shell white pigments to gypsum in the Santa Barbara area appears to be a reasonable inference from the data discussed here. Since gypsum is also prevalent as a mineral crust, there must be sources of sulphate, either from biological activity, groundwater, rainwater, or from rock components. The origin of these gypsum crusts may be complex and there is no evidence at present to identify any one source as the most probable. While the evidence for the use of shell white is inferen- tial, it was shown that diatomaceous earth could not have been used as a white pigment in any of the sites studied to date. A diatomaceous earth pigment would be subject to disruption by gypsum formation but could not be chemically transformed in the same way as a calcium carbonate white pigment.

White pigment samples from rock art sites in the Indian Wells Canyon area gave very different results to the other sites studied. X- ray diffraction data for samples from both sites in Indian Wells Canyon reveal that a relatively pure clay, halloysite (an aluminium sil- icate hydrate, Al2Si205(OH)4), was used as the white pigment. This confirms one of the sug- gestions from the work summarized by

166

Harrington which was discussed earlier. Although previous studies were not able to confirm that the white pigment used on these sites came from the Coso Hot Springs, it seems very likely that the white clay was a locally available material. The work of Whitley and Dorn [29] suggests that the red ochre used at the site was probably made from a red earth available at the hot springs; thus locally available material was probably used for the white pigment as well.

4.3 The Painted Rock site The Painted Rock site is located in an area close to three different Californian Indian groups: the Chumash, Yokuts and Salinans. Most of the rock art at the site has been attributed to the Chumash, with some Yokut elements. Paintings, engravings and cupules are located around the inner face of the rock [36].

Pictographs at Painted Rock are painted in the three colours, red, black and white, and have undergone extensive exfoliation. They have, nonetheless, survived despite temperatures in excess of 40?C during the summer months, followed by temperatures close to 0?C in the winter. Apart from exfoliation, the pictographs at Painted Rock are sometimes obscured by overlying deposits from a variety of causes. The site is important for nesting birds, particularly the prairie falcon. Some of these crusts were sampled. One was a black deposit, occurring particularly along a vertical crevice in the rock, which has been variously described as an organic, tarry deposit, as bird droppings or as a natural vein or inclusion in the rock. An X-ray diffraction study suggested that the principal component of this black crust was quartz, with some minerals of the albite-orthoclase-oligoclase type also present. From this analysis it would appear that the black material in this restricted zone of the site is a natural deposit. Another black crust material was sampled from the edge of a cave roof and the black grains separated and analyzed. The black proved to be guanine, which is not surprising since there is extensive use of the site by nesting birds and bird excrement is a ready source of guanine. A white crust overlying the rock art showed the presence of quartz, gypsum (CaSO4 2HO2) and whewellite,



calcium oxalate monohydrate. As the study proceeded it became apparent that these oxalate crusts are a common component of rock art surfaces. A white pigment from the site was difficult to sample: the surface is hard and indurated. A microscopic scraping revealed, on laboratory study, a mixture of white and black grains. The materials identified were whewellite, gypsum and perhaps some guanine, suggesting that the white pigment was, once again, a shell white, now con- verted to gypsum and intimately mixed at the surface with the other two minerals.

Green paint from graffiti, of modern origin, was sampled for identification. Under the microscope gypsum could be identified, but no inorganic component was found and the pigment could not be readily identified by infrared studies. The green particles were isotropic with a refractive index of less than 1.66 and, in the absence of copper, nickel, chromium or cobalt, are almost certainly an organic green. Even this modern paint is now difficult to remove because of the gypsum crust which adheres to the rock and paint surface. The red pigment from the site proved to be a red ochre with some haematite found by X-ray diffraction. There is a more scarlet- coloured red to be found on the outer face of the rock, but no sample could be taken from this pictograph without damage. Colour readings alone were taken.

Figure 9 Polished section in polarized reflected light from Painted Rock, x 280. It shows a charcoal layer contiguous with the rock surface, followed by a white layer and a thin layer of red ochre. The white layer is mostly gypsum, probably formed by alteration.


From an examination of the section shown in Figure 9, taken from a red ochre fragment, the following layers could be observed: first, a mixed layer of gypsum and whewellite (not visible on a sectional view); second, the red ochre layer; third, an uneven and relatively thick layer of gypsum; fourth, a layer of charcoal; and fifth, the rock surface. Because of the complexity of the events which may have occurred at these rock surfaces it may be dan- gerous to conclude from this section what superficially appears to be obvious, namely that the charcoal was applied some time before the ochre layer. It may be that the thick gypsum crust was originally white pigment, or that disruption to the surface left the original charcoal ground in situ as it carried the ochre away from the surface.

Another section from Painted Rock is shown in Figure 10, under crossed polars with the wave-plate inserted to emphasize the difference between the mineral surface crust and the pigment. Here the thick dark layer is wood charcoal and the white excrescence surrounding the black at the surface is whewellite. Below the black pigment layer the rock appears light blue and pink, with some striated organic material below the charcoal layer at the centre. This is most probably the remains of lichen, and it suggests that the surface was scraped clean before the black pigment layer was applied to the rock, or that the plant or lichen had already died before the painting was begun.

4.4 Colour reflectance measurements Measurements were made in the Commission Internationale de l'Eclairage (CIE) 1931 colour system of Y,x,y, illuminant C being selected as the standard. The recordings were taken primarily for the purpose of comparison rather than identification, and the data con- verted to the L*a*b* system, to facilitate plot- ting of the colours. The primary data are shown in Table 3 and a plot of L* against a* given in Figure 11 for red, white and black areas measured. The data obtained will prove a useful reference point for further site studies, for example of pigment fading with time, and they allow the study of variation in chro- maticity values from the Chumash sites. For example, a red clay from Santa Barbara was

167

..._

.

...' ..:;

..

. ...

.. .... .. ... . ...


Table 3 Some colour data for red, white and black from sites and pigment cakes

Site description

painted rock painted rock painted rock painted rock surface find:l surface find: B surface find:2 surface find:3 surface find:3B surface find:4 pigment cake:Cl pigment cake:C2 pigment cake:C3 pigment cake:C4 pigment cake:C5 pigment cake:C7 pigment cake:C8 pigment cake:C10 pigment cake:C 11 sun symbol:R1 sun symbol:R2 sun symbol:R3 sun symbol:L composite:R5 composite:R6 composite:R7 sun symbol:W1 sun symbol:W2 sun symbol:Bl sun symbol:B2 spoked wheel:B3 spoked wheel:B4 painted rock:Wl painted rock:W2 painted rock:W3 painted rock:B painted rock:B2 painted rock:B3 stone with red clay stone with red clay

Colour CIE

y x y

red red red red red red red red red red red red red red red red red red red red red red red red red red white white black black black black white white white black black black red red

8.2 8-8 7.7 7.6 7.4

10.3 9-9

15.7 11.8 10.9 9-6 8.3 69 9.5 67 9.3 7.8

11-3 10.0 11-7 13 4 15-8 120 103 14-7 15-6 31.4 35.4 11.0 12.1 9.3

14.9 24.0 22.8 29.4 4.9 4.8 5-1

16.4 17.3

0.410 0.433 0-412 0.416 0.490 0-395 0-413 0.444 0.412 0.423 0.467 0.446 0-422 0510 0.458 0.427 0.457 0-454 0.482 0.445 0.434 0.428 0.438 0.450 0.444 0.438 0.365 0.373 0.341 0.339 0.332 0-331 0.329 0-322 0-325 0.322 0.329 0.325 0.387 0.384

CIELAB

L* a* b*

0.357 0.358 0.352 0.352 0-368 0.351 0.355 0.367 0.361 0.361 0.366 0.354 0.357 0.366 0.357 0.354 0.354 0-365 0.362 0.361 0.362 0.366 0.362 0.355 0.359 0-359 0.356 0.358 0 345 0 341 0 335 0 334 0-339 0 335 0 332 0 336 0.337 0-338 0.363 0-362

34.3 35.7 33.3 33-2 32.6 38-4 37.7 46-5 40.9 39-3 37-1 34.6 31-6 36-9 31.1 36-5 33.6 40.1 37-8 40-7 43.3 46.7 41-2 38.4 45-2 46.4 62.8 66.1 39.5 41.4 36.5 45.5 56.1 54.9 61 2 26-3 26-0 27.1 47.5 48.7

11-7 16.2 12-9 13-6 22-5 11.0 13-6 19.6 12-7 14-6 21.0 19.0 13-2 28.3 19.0 16.2 20-5 20.0 24.9 19-4 17-7 16.4 17.9 21.0 21.2 20-4

5.1 7.2 06 1-1 08 1.0 1-0

-2.0 -0.2 -1.4 -0.3 -1.2

7.8 7.4

15-6 18.6 14-6 15.0 26-1 14.1 16.6 26.0 18-6 19.3 24-9 190 159 31.0 19.5 17.6 19-9 24.3 26-5 22-6 22.3 23-7 22.0 21.1 23.8 23-4 17.4 19.8 8-0 7.3 5-1 5-6 7.5 5-7 5-8 3.5 4.1 4.1

18.0 17.8

suggested as a possible pigment, but examination of the colour data shows its L*a*b* values to be 47.5, 7-8, 18-0. These are signifi- cantly different from typical ochre chromatici- ty values from the sites themselves; for example, one sample from Painted Rock has L*a*b* values of 35-7, 16.2, 18-6. The red clay could probably be rejected as a possible pig-

168

ment solely on the basis of the colour data, irrespective of the chemical analyses. The clay is not as 'red' as an ochre sample. Black and white pigments from site locations had values of a* close to the zero axis, with L* ranging from 26 to 36 for black and from 54 to 66 for white.

Colour recording on site was taken from


Site no.

SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SBa SBa SBa SBa SBa SBa SBa SBa SBa SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SBa506 SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SLO-79 SBNHM SBNHM


30

25 -

20 -

15 -

* 10

5

Ii 0 I I III.I I I I I1

0 *

(

-5 -

Figure 11 Table 3.

10 20 30 40

L*

Plot of L* and a* for red (#), white (9) and black (1) pigments and red clay (\); see

the least obscured area of the pigment con- cerned; the position of the reading was recorded on a Polaroid print taken at 2:1 reduction. It may be significant that the red ochres at the site of Painted Cave are brighter than those at Painted Rock: this may be due to the hue of the ochres used or to fading of the exposed art at Painted Rock.


5 Associated mineral crusts and deposits

There are many factors present in the environ- ment which will affect the long-term stability of the rock art and the pigmented surface. Physical, chemical and biochemical factors all influence the deterioration processes. As a result of the work of Krumbein it is becoming

169

0

a

50 60 70

i

I I

clear that there is an argument to be made for a complex interrelationship between rock weathering and microbial activity [37]. The chemical explanation for the formation of gypsum crusts rests on the cycle of rainwater dissolution of rock carbonates followed by precipitation of gypsum. It is possible, how- ever, that the process of gypsum crust formation is augmented by chasmolithic or endolithic microbial communities, apart from the more obvious surface communities, particularly the lichen (usually crustose) which is common on many rock surfaces in the area. Pool Rock, for example, shows an agglomera- tion of iron pigmented spherical particles within the rock section, which appear to be organic in origin.

Mechanisms for rock exfoliation at the surface may also be postulated as due to microbial activity or to chemically altered surface layers. Krumbein maintains that endolithic crust formation and subsequent leaching may lead to biogenic exfoliation because the crust may close the capillaries at the surface, pro- moting loss of the rock surface [37]. Whatever mechanisms are at work, many sites suffer from exfoliation or are in a fragile condition as a result of cracks which extend below the painted surface. In the case of the Morris Cabin Creek site, for example, a fragment which had become detached from the south- east wall shows penetration of plant material, as well as surface gypsum deposits and smaller fragments of organic material. These appear to penetrate the rock substrate along the grain boundaries between the quartz and calcite rock components.

X-ray diffraction studies revealed the ubi- quity of calcium oxalate crusts over pigmented surfaces either alone or in combination with gypsum. From recent studies, it has become apparent that calcium oxalate crusts are a widespread phenomenon over rock and stone surfaces in a variety of environments [12, 38]. Both weddelite (calcium oxalate dihydrate) and whewellite (calcium oxalate monohydrate) have been identified from rock art sites studied by the authors, whewellite being the most common in the Santa Barbara, Ventura and San Luis Obispo County areas.

The presence and continued slow precipitation of salts is one of the major factors

170


responsible for the deterioration of many of the sites examined in this study. The presence of calcium oxalates may allow eventual dating of some of the crust material by radiocarbon techniques, but some care in interpretation of these dates is clearly necessary if charcoal pigments from these rock art sites are analyzed by radiocarbon dating without an awareness of the existence of the oxalate minerals.

6 Conclusions

This report forms part of a study of Californian Indian rock art sites that it is hoped to continue. It will address some of the issues in the identification of pigments not examined to date, such as the comparatively rare blue and green pigments, and the characterization of associated mineral components of crusts or alteration products. This information should be of value not only for the conservation of the sites but also for the anthropological interpretation of the art.

The pigments which have been studied to date are the colours black, white, yellow and red. All the black pigments studied were wood charcoal, the red pigment was red ochre and the yellow pigment, yellow ochre. The white pigment was shown to be influenced by locally available materials, halloysite in the case of two sites in Indian Wells Canyon and probably shell white in the Santa Barbara County area, now altered to gypsum.

In the sites studied there was a distinct pref- erence for black as the first pigment to be laid down, with red ochre painted directly over the charcoal. None of the cross-sections examined so far shows the use of black pigment over red ochre. All of the sites have a thin crust of gypsum at the pictograph surface and gypsum now replaces the white pigment entirely. Many sites contain oxalate layers, usually of whewellite, sometimes mixed with gypsum crusts. Several of the sites are suffering from continuing physical erosion and some are in a precarious condition because of exfoliation of the rock surface on which the pictograph has been painted. Among the cross-sections examined are some which illustrate the complexity of logical inference from existing layered structures of the rock art surfaces: there may



well be different possible explanations for some of the layers revealed.

Pigment studies, in combination with the characterization of surface minerals which have formed over the pigments, are an essen- tial part of the history of the sites; their identity must be ascertained and their structural integrity evaluated before proper conservation of the sites can be envisaged.

Acknowledgements

The authors would like to thank Georgia Lee for providing access to the pigment fragments which she has collected; John Johnson, Curator of Anthropology, Santa Barbara Museum of Natural History, for expediting many official matters and arranging some site visits; Jim Blakely, local historian and naturalist of the Santa Barbara back- country; Duane Christian and Glenn Carpenter, US Department of the Interior, Bureau of Land Management; Kevin Stein, currently of CBS; Ian Wainwright, senior conservation scientist, Analytical Research Services, Canadian Conservation Institute; Stephen Home, forest archaeologist, and Bill Munger, field archaeologist, Los Padres National Forest, Golet; Professor W. Krumbein, University of Oldenburg. From the Getty Conservation Institute we would like to thank Nicholas Stanley Price, Frank Preusser, Neville Agnew, Claudia Rubin, student, Alexander Kossalopov, visiting research fellow, Eric Doehne, Michele Derrick, Michael Schilling and Mary Streigel.

References

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DAVID A. SCOTT, BA, BSc, PhD, C Chem, MRSc, FIIC, is currently head of the Museum Services section, Scientific Department, Getty Conservation Institute. His principal research interests are in the conservation and scientific examination of metals, the archaeometallurgy of ancient South America, particularly Ecuador and Colombia, and the examination of Chumash Indian rock art from California. Author's address: The Getty Conserva- tion Institute, 4503 Glencoe Avenue, Marina del Rey, CA 90292-6537, USA.

WILLIAM D. HYDER is Director of Social Sciences Computing at the University of California, Santa Cruz. He holds MAs in political science and in anthropology from the University of California, Santa Barbara. In addition to 15 years of work on the rock art in the Chumash region of California, he has conducted studies of Northern California Modoc rock art and photographed rock art on Easter Island. He is currently studying the rock art of the Basketmaker to Pueblo transition in Grand Gulch, Utah, for his dissertation research. Author's address: Social Sciences Computing, Kerr Hall, University of California, Santa Cruz, CA 95060, USA.

Resume-Une etude a 6te men6e sur de nombreux sites rupestres de Californie afin de connaitre les pigments qui ont ete utilis6s par les Indiens Chumash. L'6tude a ete faite sur des micropreleve- ments de pigments et sur des fragments de rochers peints ramass6s dans les debris du site. Les techniques d'examen ont ete le microscope polarisant, le microscope electronique a balayage, la micro-

sonde electronique, l'enregistrement de la couleur sur le site et la diffraction de rayons X sur poudre. Les pigments identifies sont l'ocre jaune, l'ocre rouge, le charbon de bois, l'halloysite (une argile blanche) et un blanc qui est probablement du blanc de coquille. Les croutes min6rales se retrouvant a la surface du rocher ont 6te egalement etudi6es, et on a mis en evidence que le gypse en etait le com- pose courant, ainsi que l'oxalate de calcium. L'etude confirme le transformation des pigments de carbonate en gypse. L'article est illustr6 par des exemples d'art rupestre qui s'est altere et par des coupes microscopiques provenant des sites 6tudi6s, en particulier Carneros Rock et Painted Rock.

Zusammenfassung-Der Beitrag befaBt sich mit Felsmalereien der Cumash-Indianer in Kalifornien, wobei die Bestimmung der dort verwendeten Pigmente im Mittelpunkt steht. Fur die Studie konnte auf Mikroproben und auf Felsmalerei- fragmente zuriickgegriffen werden, die aus dem Schutt geborgen wurden. Als Untersuchungsver- fahren wurden die Polarisationsmikroskopie, die Rasterelektronenmikroskopie (in der Form der 'environmental scanning electron microscopy'), die Elektronenmikroanalyse und die R6ntgendiffrakto- metrie eingesetzt, Weiterhin wurden Farbmes- sungen durchgeftihrt. Als Pigmente wurden gelber und roter Ocker, Holzkohle, Halloysit (ein weiBer Ton) und ein WeiB, das vermutlich aus Eierschalen hergestellt wurde, identifiziert. Die Untersuchung befaBte sich auch mit mineralischen Krustenbild- ungen auf der Oberflache der Felsmalerein. Als Hauptbestandteil fand sich dort Gips in Ver- bindung mit Calciumoxalat (Whewellit). Eine denkbare Unwandlung von Carbonaten in Gips wird diskutiert. Das Abbildungsmaterial zeigt Beispiele verwitterter Felsmalereien und Quer- schnitte, die aus den diskutierten Fundorten, ins- besondere von Carneros Rock und Painted Rock stammen.

Studies in Conservation 38 (1993) 155-173 173

a study of some californian indian rock art pigments; david a. scott and william d. hyder

Documents

study of rock art

chumash rock art

chumash art

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notable rock art

rock art fragments

existence of rock art

rock art location