Tuscan Clay Harvesting — From Earth to Ceramic Body

Clay is a hydrated aluminum silicate formed by the decomposition of feldspars through weathering over millions of years. In Tuscany, the clay is particularly rich in iron oxides (Fe2O3), which give it the characteristic red-orange color after firing. Clay particles have a diameter of less than 0.002 mm. Tuscan clay has been used since the Etruscan period (8th-1st century BCE) for producing bucchero pottery, roof tiles, and bricks.

The best deposits are found along riverbanks (Arno, Elsa, Era), at the foot of hills, in road cuts, and in eroded areas. Clay appears as a compact, smooth layer of uniform color (red, ochre, gray) beneath the humus layer. Look for areas where rain has exposed shiny, slippery soil layers that do not drain water quickly.

In Italy, the subsoil belongs to the state according to the Civil Code (art. 840). For small quantities for personal and artisanal use, collection from public land is generally tolerated. For larger quantities or from private land, always ask the owner for permission. Avoid protected areas, nature parks, and archaeological sites.

Take a handful of soil, moisten it slightly and try to form a ball the size of an orange. If the ball maintains its shape without crumbling and the surface can be smoothed with your thumb, you have found clay with good plasticity. If it crumbles, the material contains too much sand.

Roll the moist clay into a cylinder 1 cm in diameter and 15 cm in length. Lift it by one end: if it holds at least 5 cm without breaking, the plasticity is sufficient for ceramics. Bend the cylinder into an arc: if it does not crack at the curve, the clay is of good quality. These tests are called simplified Atterberg tests.

Spread the clay blocks on a cloth outdoors for 2-3 days until they are completely dry. Dry clay breaks easily into smaller fragments. Break the blocks into walnut-sized pieces using a wooden hammer. The smaller the fragments, the more quickly they will dissolve in water in the next phase.

Filter the liquid slip through a 60 mesh sieve (0.25 mm opening) to remove stones, roots, coarse sand and organic debris. The fine clay passes through with the water. The material retained in the sieve is discarded. For a more refined result, pass a second time with 80 mesh (0.18 mm opening).