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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
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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%
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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 STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS 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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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
bracciaabout corresponding to
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
bracciaabout corresponding to
175 x 43 cm
bed A or bed C with a special care
THE STONES OF THE BRUNELLESCHITHE STONES OF THE BRUNELLESCHI’’S CUPOLAS CUPOLA
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