FROM CLAY TO TERRACOTTA...
Since ancient times Impruneta area has been distinguished for the production of terracotte. Impruneta and cotto are associated traditionally (since seven centuries) and locally (for the particular soil chemistry). clay, the basic element for the production of Impruneta terracotta, is extracted from open quarries near Impruneta, a village near Florence, between the Ema and Greve valleys.
The area of extraction is fairly small - about 200 square kilometres - therefore the value of the material extracted is considerable.
Geologically speaking, it belongs to the chaotic complex of allochthonous origins; more simply it is earth made up of limestone marls and scaly clays, limited to certain areas of Impruneta and Greve. What makes this product so famous all over the world? It is due to the chemical compound of the earth in the Impruneta area called galestro.
This compound is unique throughout Italy. It contains a small part of mineral clay (65%) of which 40% is x kaolin and 10% is illite. To this particular type of soil we add 8% of calcite, 16% of aluminium, 0,5% titanium oxide and 55% silica. Galestro is not the only secret for such a global fame of the Impruneta cotto. All four Aristotelian elements need to be part of this process.
Earth: earth is purified and sift. Once all the debris are removed the soil is pulverized. The extracted clay is conserved in the sun and must be selected from the numerous waste materials.
This operation can only be carried out manually. Heavy machinery is used to grind the material and obtain a more or less grainy powder that is then riddled and stored in silos. Now the mixer and, above all, the experience of the kilnman become a vital combination: how much powder? How much water? Precise formulas do exist, but what counts most of all for the final result is the work and constant presence of the craftsmen who obtain the clay from the mix
Water: water and treated galestro are blend into a mixture.
Air: it is necessary to dry out completely the product once it's worked and shaped as it is supposed to be.
Fire: articles are placed in the furnace one above the other with a particular technique with refractory elements placed between each piece.
At the right moment, the articles are loaded into the firing chamber of the kiln, one on top of another, but separated by supports made from refractory material, using an old and special technical that requires expertise and experience.
The firing cycle is divided into two phases: 22/24 hours are required to gradually take the temperature up to 1000°C, another 10/12 hours are required to stabilise the firing at this temperature.
Kilns are nowadays heated by methane gas.
Only two days after firing is completed is it possible to remove the articles from the kiln, wet them abundantly to take out the internal lime and despatch them for sale
….WORKING THE CLAY
The Impruneta craftsmen work the clay according to ancient tradition.A vase can be shaped both: “a calco”: there are chalk moulds, that are forged from ancient moulds, on which the clay is spread and modelled to the correct thickness.
It needs a whole day to dry out and only then it is possible to take a part each element of the chalk mould and hand finish the article.
“lavoro tondo” is an other old technique. The mould is usually made from terracotta and the clay is added in strips to the outside; in this case the craftsman goes round the mould and not viceversa as with the wheel. When the clay is well compacted, the article is turned over, the mould removed and finally it is decorated by hand.
But only Very few craftsmen today are able to use the oldest and most difficult technique: the "coil method".
No moulds are used, just drawings with the measurements and it takes several weeks to finish a jar.
Our virtual itinerary inside the kiln has finished. Simple! - we thought - when we entered - A lump of clay, a splash of water...” But we now feel differently: there’s technique, creativity, tradition, the great amount of time required for the various phases of the process - if the craftsman doesn’t have the patience to wait for terracotta, he’ll never make it to the kiln room! - Our feeling is that a vase, a pot, or a fountain, are part of the history of man.