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 and it’s 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 and 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 to manifacture 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 that can be either transparent or colored. Fluxes such as germanium, alkali, 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 mixture. It aims to enhance the underlying decorative effect and make the ceramic surface impermeable.
The coloring of the glaze is achieved using natural types of earth: blue is produced from cobalt, green from copper, purple and turquoise from manganese, brown and yellow from antimony and iron, while adding tin oxide results in white.

Extrusion facilitate the low-cost manufacturing of low-value products that have a perpendicular axis to a fixed section (e.g., a brick). The production at plastic state involves a maximum water percentage of 20%, which is added to clay in the first part of the extruder (“the wetting-mixer”); a rotating screw drags the mass into a vacuum chamber, where the entrapped air is removed to achieve a homogeneous paste without bubbles, which would cause fractures in the product during firing. A final conical-profile screw compresses the mixture into the die to impart the desired shape; a cutter that is aligned with the extruder then cuts the pieces to the desired length.

Fluxes, essentially feldspars, limestone, talc, and dolomite, are used to decrease the refractoriness of the clay and to provide compact products, reacting with the material at high temperatures.

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

It is considered the highest level of ceramic production in Asian countries. Its main component is a unique type of white clay: kaolin aluminum hydrosilicate – Al2O3·2 SiO2·2 H2O.

Degreasers are mixed with clay to reduce its plasticity, providing dimensional stability to the resulting object; silica is used to increase the acidity of the mixture, along with chamotte (i.e., ground biscuit), which is more valuable and does not change the characteristics of the clay, since their chemical structures don’t actually differ much.

Colored ceramic glazes derive only from metallic oxides, since they have 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 cemented through chemical reactions that involve the components of the mass.
As the temperature rises, the following phenomena occur: the remaining water is eliminated during the process of drying until the temperature reaches 100 ºC; 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, an allotropic variation of quartz β to quartz α takes place, causing a volume decrease; between 800-1000 ºC, limestone decomposition with carbon dioxide emission occurs; between 800-1050 ºC, feldspar fusion takes place, with the resulting formation of a glassy mass that cements the material and with the formation of a compound, mullite (at 1050º C), which strengthens the mechanical resistence of piece.
There is a specific temperature trend in realtion to time, both during the heating and cooling phases, for each type of kiln and ceramic product.

Decoration is one of the final stages in the production of ceramics, after the first firing (at temperatures of almost 1000° C) and the phases of cooling and glazing. Color is fundamental: it is prepared with colored powders made from mineral oxides, fatty essence, turpentine, and in some cases, lavender essence, and then applied using specific brushes 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 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 also 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 type of clay that is used (plasticity influences the shrinkage trend) and on the shape of the object, which can dry down in a non-homogeneous way if its thickness is also not homogenous.
When it comes to bricks, drying is often carried out by stacking them above the same kilns, since they don’t require not require much care; other products are placed in discontinuous dryers, consisting of ventilated hot air chambers, or in continuous tunnel dryers, where the ceramic items are put on trolleys that go against the hot air current inside the gallery.

The term “greificazione” 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.

A slip is a binder that is used to join separately prepared ceramic pieces, and it’s usually produced by mixing water and clay.
It is also used for casting, i.e., the technique of pouring a liquid clay mixture into a plaster mold, which absorbs all the water from the slip due to its porosity.
The resulting reproduction is hollow.

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

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

Clinker is produced 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.

Clay-rich and calcareous material, characterized by a powdery structure and by a light color of various shades, including white. It is easily malleable and mainly used for pottery.

Liquid clay mixture used to coat a ceramic piece before applying color for the final decorations. Engobe should be used when the piece that is supposed to be decorated is not completely dry yet (leather hardness). It is usually white or of a similar shade (kaolin, ground quartzite) and it is applied before the glaze. The powdered engobe is dissolved in water until a creamy consistency is achieved. However, it needs to cover the underlying color of the clay (white or red) and never drip.

Among the various techniques used in ceramics production, modern industry relies strongly on extrusion, lathe calibration, pressing and casting.

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

Stoneware is mainly used to produce tiles for bathrooms and kitchens. It is made from natural clay combinations that produce vitrified ceramics. The temperature needs to be between 1200° C and 1350° C.

A product made from ceramic material (majolica, porcelain, stoneware, etc.) and with a geometric shape that is usually used for wall and floor coverings.

The raw materials used in 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 achieved with mixtures of potassium silicates and borates, lead, etc.
They are applied to products to hide the color of the paste, eliminate porosity, and add a pleasing aesthetic appearance.
Several coating application techniques are usually used: from immersing objects in aqueous baths (glazes, engobes, and covers) to spraying (glazes, especially in tile production), from salting (stoneware) to brushing (art pieces).

It is a type of ceramic material that presents a coloration ranging from yellow to red after firing, 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 object.
Thanks to its stability, lightness and resistance to aging due to its porosity, terracotta is the most widespread construction material, commonly known as brick.