opera di santa maria del fiore the stones of the ...lapideiculturali.unifi.it/pdf/cupola-en.pdf ·...

THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLAMassimo Coli, Margaret Haines & Paolo Bianchini

Opera di Santa Maria del Fiore

THE CUPOLATHE CUPOLA … THE MONUMENT

http://www.operaduomo.firenze.it/cupola/home_eng.html

Brunelleschi conceived and vaulted the Cupola in the years 1417-1436

Brunelleschi was able to vault the Cupola without scaffolding making it self-sustaining

To that purpose Brunelleschi introduced new techniques and a selected use of building materials

The archives of the Opera show that particular materials were chosen for specific uses

THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA

http://www.operaduomo.firenze.it/cupola/home_eng.html

The analysis of the documentation outlines four types of material each one with its own specific use:

PIETRAFORTE: this stone was used for the mansory

of the Tamburo, its over-structure and the first rim of the Cupola

MARBLE: tiles and blocks of white marble were used for aesthetic purpose in the ribs and for the Lanterna

BRICKS: bricks specifically built in special sizes were used for the masonry of the eight webs

MACIGNO: this stone was used to build three stone-chains, thought by Brunelleschi to strength the Cupola, and its top-look (“Serraglio”)

The archives of the Opera del Duomo

envisage the detail that Brunelleschi put in ordering these materials, the quality, quantity and sizes required and where they had to come from

… THE MATERIALS


THE PIETRAFORTEPIETRAFORTE: is a dark-brown quartz-

calcareous arenaceous turbidites in medium-

to thick-beds (10-70cm), with calcite cement, presence of Tb-e Tc-e

Bouma

structure, ratio A/P ≈

1

The oldest quarries of the Pietraforte were in the hills right south of Firenze, facing the Arno river

Remains of these quarries are locally still visible or are recorded by local name as “quarry lane”

Due to its proximity to the town and an easy down-

slope transport the Pietraforte was widely used for the majority of the buildings of Firenze since the Roman time


The exploitation of the Pietraforte was done bed by bed by using the stratification and the two main natural joint sets (almost orthogonal and from a few tens of centimeters up to a couple of meters spaced) in order to dismantle the rock-mass

The raw blocks so obtained had the high equal to the bed highness, and length-wide according with the joint sets spacing, if necessary they were subsequently sized to the requested dimensions

During the centuries all the quarries of Pietraforte were dismissed and subsequently incorporated by the city expansions or reclaimed, as the Boboli Garden which represents the best example in the world of the re-use of a degraded old quarry site


Petrographically, Pietraforte is a fine-grained 0.15mm lithic

sandstone made in the same proportion by silicatic

grains (quartz, feldspars and magmatic fragments) and carbonatic

grains (dolostones)

Grains are bounded by a mainly calcitic

matrix that makes the rock particularly strong

Mechanical parameters are high because of compactness established in the stone by the re-crystallization due to diagenesis

In fresh cut the sandstone has a grey color, but is easily oxidized acquiring an ochre brown color on buildings due to the oxidation of iron, this process proceeds very quickly from the surface to the inside, without cohesion decrease

Pietraforte is often characterized by laminations of a convolute

type (Tc

Bouma

layer)

The Pietraforte main physical-mechanical properties are:-

Unit weight = 27 kN/m3

-

UCS normal to bedding = 140 MPa (cubic samples)-

UCS normal to bedding = ----

MPa (ISRM standard)-

Young modulus = ---

GPa- Poisson’s ratio = ----- Porosity = 4-6%

Lab Lab tests

tests in progress

in progress


The masonry of the Tamburo

over- structure was built in regular row,

about 15-20 cm high, of Pietraforte

In the masonry, beams of Macigno and iron bars were inserted, in order

to support marble revetments


In the Cupola the white marble were used in blocks for:

a) the external revetments of the ribs

b) the Lanterna, whose weight was thought to luck the Cupola

According with the Opera archives the marble come from Carrara

(A -

northern Tuscany) and also from Campiglia

(B -

southern Tuscany)

THE MARBLE

A

B

Firenze

The main supply resulted to had been from Carrara


Marble was transported by means of boats and wagons

In order to avoid numerous changes of transport means Brunelleschi built a special amphibious boat called “Badalone”

for directly transporting the marble to Firenze by sea and on the Arno river, but it was not a success!

In the quarry yard the block were sized and roughly dressed to their final shape in order to avoid imperfections and ruptures once transported

Once in the yard of the Cupola the blocks were finished and polished before to be put on site


Carrara

Marble

comes from the Apuan

Alps metamorphic core complex close to the town of Carrara

and the ancient Roman Luni

Carrara

Marble is worldwide famous thanks to Michelangelo and its masterpieces, first of all the David

Carrara

Marble is still extracted in many quarry for ornamental purpose, it is highly improbable to recover the exact quarry where the marble of the Cupola comes from

Carrara

Marble is composed by plus than 98% of calcite crystals, with grain size 0.5-0.6 mmThe Carrara

Marble main physical-mechanical

properties are:- Unit weight = 27 kN/m3

- UCS = 130 MPa (cubic samples)- UCS = 96 MPa (ISRM standard)- Young modulus = 49.5 GPa- Poisson’s ratio = 0.274- Permeability = 0.2%


Campiglia

Marble comes from a contact metamorphism due to a plutonic stock

At present near Campiglia

only a few marble quarries are now in use but for industrial purpose

Recently we found the ancient Campiglia

Marble quarry sites, still in the Earls of the Gherardesca’s

property, with traces of the ancient cultivations

According with some Authors the Campiglia

Marble was used for the Lanterna

and the external revetment of the Tamburo

and Abside

Campiglia

Marble is composed by plus than 98% of calcite crystals, grain size 0.5-0.6 mm

The Campiglia

Marble main physical-

mechanical properties are:- Unit weight = 27 kN/m3

- UCS = 130 MPa (cubic samples)- UCS = 96 MPa (ISRM standard)- Young modulus = 49.5 GPa- Poisson’s ratio = 0.274- Permeability = 0.2%

1478FILIPPO NERI


The Arno river and its tributaries periodically flooded the Florentine plane leaving thick deposits of silts and clays, mainly referable to CL (inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silt clays, lean clays)

of the USCS which is well suited for making bricks

THE BRICKS

Firenze was famous for its kilns and the skill of its workers

The archives of the Opera report that the kilns for the bricks of the Cupola were in the near western country side: A) Badia

a Settimo, B) Lastra

a Signa, C) Campi

Bisenzio

Several kilns were also in the eastern area between the old II and the new III ring of the city-wall

City kilns were soon incorporated into the city and transformed in houses

Kilns survived in the country side until the second half of the XX century, when they were dismissed and the areas reclaimed for houses


The Cupola bricks were made in the same way they are still made to-day in some part of the world:

- clay is removed by the ground surface

- clay is handy pressed into wooden/iron forms

- bricks are cocked in kilns

- in Tuscany they had the form of squat tower


By order of Brunelleschi bricks were made into special forms in more sizes of about: 17x34x5 cm

22x44x5 cm22x22x5 cm

The bricks of a) and b) types were placed by flat according with a “cordablanda” geometryBricks of c) type were placed vertically about every 1.2 m The combination of the two sets describe a herringbone patternFor the corner of the Tamburo

and the first layers of the Cupola ribs special angular bricks (135°) were used in order to avoid segmentations in the masonry


To build the Cupola same millions of bricks were used, yearly supplied in a number of about 400,000

In the Cupola yard usually about 40 skilled workers were employed

It resulted that each worker put on site no more than 20 bricks a day, with this rhythm the Cupola had been growing about 2.5 m a year

These figures envisage the importance that Brunelleschi devoted to organization, good practices and mortar set

Recent surveys outlined for the Cupola a very good masonry, with bricks and malt well fit


The malt come from the Pontassieve

area (A), east of Firenze, where quarries for cement, exploiting the “Alberese”

limestone, had been acting until the 1970’s

Special tiles of “cotto”

(cocked) were used to cover the Cupola webs, the cotto

come from the Impruneta

area (B), south of Firenze

Cotto

is a best graded brick which has as row material the silty-shales

of the Argille

a Palombini

Fmt. largely outcropping in this area

Cotto

from Impruneta

is still on production and high prized

AA

BB


In the early 1970’

four cores were exceptionally drilled in the inner masonry of the Cupola for scientific and technical purpose

The material of the cores was used to determinate the physical-mechanical properties of bricks and malt

Due to the scarcity of material the tests were done on prismatic samples 3x3x6cm


The physical-mechanical properties of bricks and malt were determined according with RILEM recommendations (Methodes

d'essai des pierres naturelles et artificielles: I. Pierres naturelles; II. Elements

a maconner

en terre cuite)

Bricks main physical-mechanical properties are:

- Unit weight = 15.5 kN/m3

- UCS = 27.6 MPa

-

Tensile strength: 2,66 MPa

-

Young modulus = 11 MPa

- Poisson’s ratio = 0.18

- Porosity = 35%

Malt main physical-mechanical properties are:

- Unit weight = 17.5 kN/m3

- UCS = 19.6 MPa

-

Tensile strength: 2,05 MPa

-

Young modulus = 7.85 MPa

- Poisson’s ratio = 0.27

- Porosity = 28.2%


THE MACIGNOMACIGNO: is a light-grey quartz-feldspatic

arenaceous turbidite in medium-

to thick- beds (10-70cm) and banks (up to 10m), with clay matrix and a scarce (up to 15%) calcite

cement, presence of Ta-d Tb-e Bouma

structure, ratio A/P >

1

The Macigno

quarries were in the hills north and south of Firenze

The excavation of the Macigno

became with the Etruscan in the VII century B.C. and ended in the last decades of the XX century

Remains of the Macigno quarries are largely still

visible, only a few of them had been reclaimed

Macigno

was largely used in the buildings of Firenze for strengthen the masonries and for ornamental purposes, town furniture and stone paving


Petrographically, Macigno

is a medium-coarse-grained grey-wacke

made by quartz, feldspars, micas, fragments of metamorphic and magmatic rocks

The matrix is quite abundant and is made by illite, kaolinite

and chlorite-vermiculite

The grain size of the best graded beds used in architecture varies from medium fine to medium, around 0.25-0.3mm

Macigno

has a bluish-grey color in fresh cut, while under strong alteration, owing to

the iron oxidation, it takes on an ochraceous

color

Macigno

best graded beds have no sedimentary structures and high workability, for these reasons Macigno

is one of the most widely used stone in the Firenze architecture for decoration purposes by Brunelleschi, Michelangelo and Vasari

The The MacignoMacigno

main physicalmain physical--mechanical properties are:mechanical properties are:

-- Unit weight = 26.7 kN/mUnit weight = 26.7 kN/m33

-- UCS normal to bedding = 90 MPa (cubic samples)UCS normal to bedding = 90 MPa (cubic samples)

-- UCS normal to bedding = UCS normal to bedding = --------

MPa (ISRM standard)MPa (ISRM standard)

-- Young modulus = Young modulus = ------

GPaGPa

-- PoissonPoisson’’s ratio = s ratio = --------

-- Porosity = 4Porosity = 4--6%6% Lab Lab tests

tests in progress

in progress


Brunelleschi in his design talks about the use of the Macigno

for a special purpose:

“… in order to strength the Cupola with stone chains of strong Macigno clamped with iron …”

Later Authors do not agree the Macigno chains were able to play that role, but

this question is out of our purpose

In the Cupola, Brunelleschi used the Macigno

to built three chains, which link the inner and the outer vaults of the Cupola, and the top-lock: the Serraglio

Serraglio

Serraglio


At the beginning of the construction of the Cupola (1421) a first order for 600 beams of Macigno

was done, with these specific sizes:

4 x ¾

x ¾

braccia (1 braccio = 58.32cm)about corresponding to

233 x 43 x 43 cm

ORDERS FOR MACIGNOORDERS FOR MACIGNO

These beams had to come from Trassinaia

quarry and must be of these specific quality:

galazone, falda grossa, falda gentile, masso

Further orders were done in the years 1430, 1432 e 1433 for beams of these sizes:

8 braccia in length about corresponding to

466 cm48 beams of 3 x ¾

bracciaabout corresponding to

175 x 43 cm128 beams of:

falda grossa, falda gentile, masso


In the Cupola we surveyed all the Macigno

beams which is possible to see in the passages between the two vaults and in the Serraglio

All these elements have dimensions coherent with those reported in the archives of the Opera, in particular:

Jambs: 40 x 40 x 190 cm43 x 43 x 170 cm43 x 43 x 180 cm

Lintels: 25 x 40 x 140 cm30 x 43 x 130 cm26 x 40 x 140 cm

These sizes are very constant and correspond to the measures of ¾

x ¾

of braccia

No beams with the length of 8 braccia were surveyed in the visible parts of the Cupola


As reported in the archives, by specific order of Brunelleschi all the Macigno

for the Cupola had only to came from the quarry of Trassinaia

in the Alessandri

property

Detailed analysis of historical and recent cartography, together

with landscape, geological and archeo-mining investigations, have us allowed to confidently identify this site in an ancient, abandoned quarry site settled on the right-side of a creek, unnamed at present but originally denominated “Trassinaia

creek”

below the Vincigliata Castel


Our survey evidenced that in the Trassinaia

quarry only three beds of Macigno

were cultivated

Solely by the help of the old last Macigno

stonecutter we were able to assign to each one of these three sandstone beds the quality name used by Brunelleschi

C

B

A


ON THE BASE OF THE BED THICKNESS, JOINT SPACING AND QUALITY RECONEISSANCE MADE BY THE STONECUTTER THESE

CORRESPONDENCE CAN BE OUTLINED

beams: 4 x ¾

x ¾


233 x 43 x 43 cm

bed A or bed C with a special care

beams of 8 braccia in length about corresponding to

L = 466 cmonly from bed A

48 beams of 3 x ¾


175 x 43 cm

bed A or bed C with a special care


opera di santa maria del fiore the stones of the ...lapideiculturali.unifi.it/pdf/cupola-en.pdf ·...

Documents