Glossary

A compound added to a substance (or material) to improve its characteristics.

A type of ceramic firing achieved by firing the body and surface layer at different times. The first firing consolidates the body, while the second stabilizes the surface glaze. Compared to single firing, biscuit firing allows for more brilliant glazes, better color definition, and lighter weight products.

Named after the Chinese locality Kaoling, it is a high-quality clay with the chemical formula Al2Si2O5(OH)4, used in porcelain manufacturing, the paper industry, and refractory materials production. It is essentially composed of pure kaolinite, produced by the action of meteoric water on feldspar.

Thin veins, cracks on the surface of ceramics and majolica. If unintended, crazing indicates a defect due to a different thermal expansion coefficient between the body and the glassy coating.
Craquelé is a painting technique that creates a web of fine cracks on a glazed surface or object, giving it a pleasant aged or antique appearance.

Casting or Slipcasting is a technique used for forming some ceramic products. A suspension of water and clay powder with a small dose of electrolytes (usually sodium silicate or sodium carbonate) is poured into a porous mold (plaster). The water is absorbed, leaving only the solid shell (Green) that takes the shape of the mold itself.

Glass-like coatings, transparent or colored. Fluxes such as germanium, alkalis, or borates are added to the glaze to lower the melting point.
Waterproofing by glazing is achieved by completely immersing the object in the glaze. It aims to enhance the underlying decorative effect and make the ceramic surface impermeable.
The coloring of the glaze is achieved using natural earths: blue is obtained with cobalt, green with copper, purple and turquoise with manganese, brown and yellow with antimony and iron, while adding tin oxide results in white.

Extrusion allows for the low-cost production of low-value artifacts that geometrically have a perpendicular axis to a fixed section (e.g., a brick). The plastic state processing involves a maximum water percentage of 20% added to the clay in the first part of the extruder called the wetting-mixer; a rotating screw drags the mass into a chamber, placed under vacuum, where the entrapped air is removed to obtain a homogeneous paste without bubbles, which would cause fractures in the artifact during firing. A final conical-profile screw compresses the mixture into the die to impart the desired shape; a cutter in line with the extruder cuts the pieces to the desired length.

Fluxes, essentially feldspars, limestone, talc, and dolomite, serve to decrease the refractoriness of the clay and, reacting with it at high temperatures, provide compact artifacts.

A mixture of clay and other substances with water, which is shaped and then consolidated through firing processes to manufacture majolica, porcelain, terracotta, etc.

Considered the highest level of ceramic production by the Orientals. Its main component is a particular white clay: kaolin aluminum hydrosilicate – Al2O3·2 SiO2·2 H2O.

Degreasers, mixed with clay, reduce its plasticity, providing dimensional stability to the artifact; in practice, silica is used, which gives an acidic character to the mixture, and chamotte, i.e., ground biscuit, more valuable, which, not differing chemically from the clay, maintains its characteristics unchanged.

Colored ceramic glazes derive only from metallic oxides, having to withstand high firing temperatures.
Oxides and fluxes can be used to create your own glazes. Mastering these techniques takes some time, as many trials are needed to achieve a satisfactory result, especially for glazes.

Ceramic support of the first firing, without coatings and vitrifiable decorations.

A type of predominantly sandy clay. It appears as a very hard and compact sediment, with a very fine grain size, varying in color from light brown to light gray, with ochre-colored streaks.

Composite material consisting of ceramic (CER) and metallic materials (Met). Cermet is designed to have the optimal properties of both ceramics, such as high-temperature resistance and hardness, and metals, such as the ability to undergo plastic deformation. Generally, the metallic part is 20% of the volume.

Firing transforms the mixture from incoherent to a cemented whole through chemical reactions that occur between the components of the mass.
As the temperature rises, the following phenomena occur: up to 100 ºC, the remaining water is eliminated during drying; at 250 ºC, silica transitions to a new allotropic state (cristobalite) with a consequent increase in volume; between 450-600 ºC, the clay decomposes into free oxides with the release of combination water and consequent volume decrease; at 575 ºC, allotropic variation of quartz β to quartz α, with volume decrease; between 800-1000 ºC, limestone decomposition with carbon dioxide emission; between 800-1050 ºC, feldspar fusion with the formation of a glassy mass that cements the paste and the formation of a compound, mullite (at 1050 ºC), which imparts mechanical strength to the piece.
For each type of kiln and produced object, there is a specific temperature trend as a function of time during both the heating and cooling phases.

Decoration is among the final stages of the ceramic production process. Decoration occurs after the first firing (at temperatures of almost 1000° C), cooling, and glazing. Color is fundamental: it is prepared with colored powders based on mineral oxides, fatty essence, turpentine, and in some cases, lavender essence, and is applied using brushes indicated based on the size of the design. Oxides can be used to color mixtures and slip.

This phase is always necessary before firing the shaped piece, as rapid evaporation of the water contained in the artifact would cause crack formation. During drying, the outer part of the piece first loses water, creating a contraction of the paste (shrinkage), then the inner part loses water with a consequent movement towards the outside, creating porosity; in this phase, there is no further contraction as the mixture is now in a dry state and the mobility of the particles has effectively decreased. Moreover, these phenomena vary depending on the nature of the clay used (plasticity influences the shrinkage trend) and the shape of the object, which, if of different thickness, presents differently dried areas over the same time. For bricks, drying is often carried out by stacking them above the same kilns, as the artifact does not require much care, while for other products, discontinuous dryers consisting of ventilated hot air chambers or continuous tunnel dryers are used, where the artifacts travel on trolleys through the gallery in countercurrent to the hot air.

The term is sometimes used as a synonym for vitrification, not very intense, referring to tiles like stoneware. It is measured in relation to water absorption capacity: less absorption means more vitrification.

Obtained by mixing water and clay, it is a binder used to join separately prepared ceramic pieces.
It is also used for casting, i.e., the technique of pouring the liquid clay mixture into a plaster mold, which, being porous, absorbs all the water from the slip.
The resulting reproduction is hollow.

A technique for shaping ceramic pieces in the form of solids of revolution, consisting of shaping with a gauge, i.e., a metal template, the paste rotated by the lathe. Lathe calibration is used for artifacts with shapes of solids of revolution (plates, vases, cups). The processing, also in the plastic state, involves a water percentage in the mixture of 30%.

A place from which mineral materials intended for construction are extracted, whether stone, sand, or clay; the quarry can be underground (tunnels) or open-pit, where the material to be extracted is reached directly from the outside. The extraction activity proceeds by cutting steps and quarry fronts into the rock.

Clinker is obtained by firing raw materials at very high temperatures, around 1250 °C, almost inducing vitrification of the material. This treatment makes the material dense and resistant, giving it an extremely hard and non-hygroscopic surface.

Clayey-calcareous earth, characterized by a powdery structure, light in color to white, easily moldable, and mainly used for pottery.

Liquid clay mixture used to coat a ceramic before applying the final decoration colors. Engobe should be used when the piece to be decorated is not yet completely dry (leather hardness). Generally white or almost (kaolin, ground quartzite), it is applied before the glaze. The powdered engobe is dissolved in water until a creamy consistency is obtained. It must, however, cover the underlying color of the clay (white or red) and must not drip.

In the ceramics industry, shaping. Among the various techniques used, modern industry highlights extrusion, lathe calibration, pressing, casting.

Ceramics do not only refer to the material but by extension also to the product composed of that material.
The products in question can be numerous.

Stoneware is mainly used to produce tiles for bathrooms and kitchens. It is obtained from natural clay combinations that produce ceramics known as vitrified. A temperature between 1200 °C and 1350 °C is required.

Element of ceramic material (majolica, porcelain, stoneware, etc.), with a geometric shape, used for wall and floor coverings.

The raw materials of the ceramics industry are classified as fundamental (clays), secondary (degreasers and fluxes), and complementary (coatings and colors).

Ceramic coatings are glassy, and their composition is obtained with mixtures of potassium silicates and borates, lead, etc.
They are applied to artifacts to hide the color of the paste, eliminate porosity, and impart a pleasant aesthetic appearance.
Coating application techniques involve immersing objects in aqueous baths for glazes, engobes, and covers; spraying for glazes, especially in tile production; spraying for glazes and glazes; salting for stoneware; brushing for art objects.

It is a type of ceramic that, after the firing process, presents a coloration ranging from yellow to red, thanks to the presence of salts or iron oxides.
The presence of iron oxide improves the mechanical resistance of the fired ceramic, contributing to vitrification and thus reducing the porosity of the artifact.
Thanks to its stability, resistance to aging, and lightness given by its porosity, terracotta is the most widespread construction material, known as brick.