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THE RENAISSANCE TECHNIQUE
The basic raw material, red clay or chalky clay, was dug from river beds or pits, impurities were removed and the clay was well kneaded to remove any air pockets within the clay before it was thrown on the potter's wheel or pressed over or into plaster moulds to form vessels. The first firing took place at about 1,000 degrees centigrade in a wood burning kiln. After removal, the pots, now either a pale reddish brown (terra cotta) or cream in color were ready for glazing.
The making of the tin glaze or 'bianco' (white) was a complex process. First, white sand and potash (potassium carbonate especially in its crude impure form obtained from wood ashes) in the form of calcined wine lees (from the inside of barrels) were heated in a pot until they fused into a glassy lump. This was then finely ground and suspended in water with oxides of lead and tin, the last rendering the glaze white and opaque. This sloppy liquid was then applied to the pots, and after a short period of drying time they were ready for painting. The pigments of the color when brushed on the glaze sink into the glaze. Decorators had to be extremely deft because once a mistake was made it could not be corrected. Their pigments were based on metal oxides: cobalt for blue; copper for green; antimony for yellow; manganese for purplish-brown; tin for white. Red was obtained by fluxing Armenian bole with lead, but it was difficult to fire successfully and therefore occurs infrequently on renaissance Maiolica. The pots were then fired again at 950 degrees centigrade.