How ceramics are made

Before the discovery of electricity, ancient kilns used human power to move the wheels.
Around the Middle Ages, the potter’s wheel took on the appearance it kept until a few years ago; this type of wheel is still widely used in countries where modern technology is less prevalent.
The ancient wheel is a very simple machine, consisting of two wheels of different sizes, one much larger and heavier than the other, connected by a shaft.
The larger wheel is placed at the bottom, so that, by pushing it with the foot, the smaller wheel also rotates in an identical way.
The inertia of the lower wheel’s movement, caused by its greater weight, allows the potter to work the clay without needing to continuously push the machine and avoiding the risk that the rotation might abruptly stop.
Such simple mechanism was integrated into a bench, where the operator, called a turner, could sit.

In order to color ceramics that were already covered with a metallic coating, colors also made of metal oxides were used.
The process remains essentially the same to this day.
Colors can be divided into two categories: simple formulas, formed by the oxide of a single metal, and compounds, produced by mixing different metals and other substances.
Oftentimes the ceramic painter can’t see the final hue that the color will take on before the second firing.
Colors, in fact, achieve their brilliance only after being fused again in the kiln.

In the past, whenever potters wanted to fix a metal oxide-based coating film on a piece of ceramic that was only fired once, they would usually immerse the biscuit in a tub filled with liquid glaze or enamel, a finely ground compound that was diluted with water. This technique is still used today.
The immersion (dipping) is carried out by workers called dippers, who must make sure not to touch the ceramic piece with their hands before immersing it, as the natural oils of the skin would prevent the metallic substances from adhering well to the biscuit.
Due to its porosity, the biscuit quickly absorbs the liquid part of the compound, leaving the metallic parts on the surface.
Majolica pieces require a specific treatment: after they’ve been dipped in enamel and left to dry, their ceramic surface can be decorated by painting it or scratching the colored parts.

The firing phase was a particularly delicate process that required the contribution of extremely experienced people called kiln workers. To make the most of the available fuel, they would try to fill the kiln with as many objects as possible, arranging them one on top of the other in orderly stacks (stacking).
Kiln workers would usually distance products that were glazed or vitrified with silica-metallic coatings from one another, using special supports that often took the form of a tripod. This technique was meant to prevent the fusion of the coating from welding them together during firing, and it is still used today.
In traditional kilns (not the muffle ones), objects were placed in special containers, called boxes or cases, before firing, in order to prevent flames and other combustion residues (smoke, soot, dust) from damaging the glaze film. Inside these boxes, the items were distanced from one another with triangular supports, which were inserted into the walls and protruded towards the inside of the cases themselves.
Once full, the kiln was sealed by closing the access door (usciale) to the firing chamber with a temporary wall: the fire was thus forced to exhaust towards the outside, by passing through it completely.

We can identify three fundamental methods of ceramic decoration that were used in the past: painting, scratching (or “graffito”), and the addition of clay substances in relief.
While painting involves applying one or more colors with a brush over the surface, the “graffito” method requires removing the coating (engobe or enamel) when it is still fresh, using a pointed tool or a prong (stick).
The superficial layer with engobes is removed to reveal the reddish color of the underlying biscuit: with this system (called “graffito a punta”), only the outlines of the figures are drawn, which can then be perfected by painting them.
It is called “graffito a fondo ribassato” (with a lowered background) when the outlines are engraved by removing more extensive parts of the engobes with a wide-pointed tool or prong.
The method of adding material in relief, usually the same clay as the biscuit, was widely used in Northern Europe (Northern Germany and England) in ceramics known as slipware.
For painted decoration, specifics artifices have also been adopted to make the color emerge on the surface of the decorated object.
In Spain, the lines that separated the decorations used to be outlined with a small cord, which was soaked in fatty substances that would would prevent the colored glazes from adhering during firing. Burning the cord would leave those areas, where the color was not meant to be, uncovered, due to said fatty substances. This process, called “cuerda seca”, would preserve the clearly-definied margins of the decorations.