Ceramics Glossary
Find definitions for ceramic terms, materials, techniques, and tools.
Discover glossary terms
Opaque (Glaze)An opaque glaze is one that, thanks to the addition of opacifiers, does not allow to see through its surface, thus hiding the clay underneath. Unlike transparent or semi-opaque glazes, these generate a uniform and solid chromatic coverage, highlighting the colors of the glaze and preventing the tonal variations of the clay body from affecting the final result.
Historically, the development of opaque glazes, particularly white glazes, was motivated by the desire to imitate the aesthetics of Asian porcelain, famous for its purity and luminosity. Islamic and European Renaissance cultures found in opaque glazes an ideal base for applying polychromatic decorations, intensifying contrast and enhancing hand-painted details. Today, opaque glazes are used both in industrial production and in artisan workshops, as they are useful to uniform the finish, hide imperfections in the clay and simplify the application of decorations.
SpeckledSpeckled refers to the appearance of spots or specks of color on the surface of the piece. This effect can be achieved by the addition of colored particles or by the irregular application of the glaze, resulting in a rustic, textured or speckled appearance that adds character and depth to the ceramic. Speckling is a decorative technique that can vary in intensity and distribution, depending on the amount and size of the color particles used, as well as the application technique employed.
Speckeld can be achieved in a variety of ways, such as the addition of metallic oxides in the glaze or clay, the application of diluted glazes or engobes with pigments, or by painting and stamping methods that create irregular color patterns. This effect is popular in handmade and contemporary ceramics because of its ability to mimic the appearance of natural materials such as stone or aged wood, bringing an organic and authentic aesthetic to the pieces.
FlangeThe flange is a functional and aesthetic element in the architecture of ceramic containers with lids. It is commonly presented as an internal step, a lip or a protruding surface at the mouth of the container, whose main mission is to keep the lid centered and stable, preventing its displacement.
In utilitarian contexts, a well-designed flange guarantees the protection of the contents, avoids spills and improves the preservation of aromas and flavors. On the other hand, in ornamental or design pieces, the flange can assume a decorative role, adding aesthetic nuances, visual rhythms or textural contrasts. Material, thickness, height, shape and finish influence the quality of the fit between lid and body, demanding careful planning during modeling and post-firing calibration.
SandsSands are fine particles of minerals, primarily silica, that are incorporated into the clay or glaze mix, or applied directly to the surface of the pieces to provide texture and unique visual effects. Sand can be mixed with clay during mass preparation to modify its physical properties, such as plasticity and resistance to cracking, or it can be added to glazes and engobes to create rough, textured surfaces. In addition, sand is used as a surface decoration, either applied before firing or embedded in the glaze, providing a visually attractive finish and, in some cases, improving the functionality of the piece by increasing its resistance to wear or heat.
The inclusion of sand in the clay can influence the internal structure of the ceramic piece, providing greater mechanical strength and reducing porosity. This is especially useful in utilitarian pieces that must withstand daily use and temperature variations. The texture added by the sand can also be used for aesthetic effects, creating rough, speckled or grainy patterns that enrich the appearance of the ceramic.
There are different types of sands used in ceramics, each with specific characteristics that affect the final result of the piece. Silica sand, for example, is one of the most common due to its purity and its ability to improve the thermal stability of ceramics. Feldspar sand adds vitrifying properties to the glaze, improving its luster and strength. Other sands, such as quartz sand or volcanic sand, are used to create unique textured effects and to increase the durability of the pieces.
GlassGlass in ceramics refers both to the vitreous component that forms in ceramic glazes and to the direct use of glass fragments or powder to decorate the surface of the pieces. In glazes, glass is formed by melting during firing, creating a hard, shiny and resistant layer that not only beautifies the piece, but also waterproofs it and protects it against physical and chemical damage. This vitreous coating provides a uniform and aesthetically appealing finish. In addition to use in glazes, glass shards or crushed glass powder can be applied directly to the clay prior to firing for unique visual effects, such as glossy, speckled or textured surfaces, which add an extra dimension to the ceramic piece.
Glass in ceramics not only serves an aesthetic function, but also enhances the functional properties of the pieces. By acting as a vitrifying agent, glass increases the water resistance and durability of the pieces, making them more suitable for utilitarian applications such as tableware, vases and cookware.
Kanthal wireKanthal wire is a metallic alloy composed mainly of iron, chromium and aluminum, recognized for its high resistance to oxidation and ability to withstand extremely high temperatures without degrading. In the field of ceramics, Kanthal wire is mainly used as a heating element in electric kilns due to its stability and durability at high temperatures. This material is essential for the manufacture of modern kilns, as it allows precise temperature control, ensuring uniform and efficient firing of ceramic pieces.
The Kanthal wire is installed inside the kiln in the form of coils or resistors, evenly distributed to ensure homogeneous heat distribution. Its ability to maintain a constant electrical resistance even under high temperature conditions makes it an ideal choice for ceramic applications that require complete and consistent vitrification. In addition, the longevity of Kanthal wire reduces the need for frequent replacements, thus optimizing time and resources in ceramic workshops and factories.
Boric acid (H₃BO₃)Boric acid is a key component in the formulation of ceramic glazes, where it acts as a flux, helping to reduce the melting point and facilitating surface vitrification. This compound is especially valued in low-temperature glazes, as it allows glossy and glazed finishes to be achieved without requiring high-temperature firings, which is ideal for utilitarian and decorative ceramics.
In addition to improving melting and gloss, boric acid contributes to glaze stability, reducing problems such as crazing/cracking or bubbling during firing. It is also known to enhance the intensity of colors, especially in transparent and glossy shades, due to its ability to create a clear and luminous vitreous layer on the surface.
SaggerA sagger is a box made of refractory clay used inside kilns to contain and protect the glazed pieces during the firing process. These boxes are specifically designed to withstand the high temperatures of the kiln, preventing the pieces from coming into direct contact with the flames, gases or smoke generated during firing, which could negatively affect the glazing results. Being made of refractory materials, the saggers are able to withstand extreme temperatures without damage, allowing them to be reused in multiple firings.
The saggers are particularly useful in kilns with oxidizing atmospheres, where oxygen in the environment can cause alterations in the colors and effects of the glaze, or in processes where fire and smoke can have an undesirable impact on the quality of the glaze. By placing the pieces inside these refractory boxes, they are isolated from the direct effects of the kiln atmosphere, ensuring a more controlled firing and more predictable results.
In addition, gasses are also used in reducing atmospheres, where the aim is to control the effects of gases on the fired parts. In this environment, the low-oxygen atmosphere can influence the colors and characteristics of the glaze, and the use of saggers allows this environment to be managed in a more controlled manner, preserving the integrity of the glaze.
Iron chromate (FeCr₂O₄)Iron chromate is a ceramic compound that is mainly used in glazes and engobes to generate a wide range of colors, which can vary from vibrant greens to dark browns, depending on several factors, such as firing conditions and the concentration of the material in the mixture. This pigment is especially prized in high-temperature ceramics, and is frequently used in the manufacture of stoneware and porcelain ware due to its ability to maintain color stability and quality at high temperatures.
It is known for its ability to change color according to kiln conditions, which gives it great versatility. In reducing atmospheres, where oxygen is limited, iron chromate tends to produce darker, metallic and deeper colors, which can include shades of brown and black. On the other hand, in oxidizing atmospheres, where oxygen is present in abundance, the colors tend to be softer, creating lighter, more vibrant ranges of greens and browns. Iron chromate is not only appreciated for its ability to modify colors, but also for its durability and resistance to extreme kiln conditions, making it an interesting component for high quality ceramic glazes.
VitrifierA vitrifier in ceramics is a chemical agent added to clay or glaze mixtures to promote vitrification during firing. Vitrification is the process by which clay is transformed into a hard, non-porous material at high temperatures, developing properties such as water and wear resistance. Vitrifiers help to reduce the firing temperature required to achieve complete vitrification, improving the efficiency of the process and the quality of the final pieces.
In addition, vitrifiers can influence the texture and finish of the ceramic, allowing for better adhesion of glazes and a smoother, more uniform surface. By controlling the amount and type of vitrifier used, the properties of the clay and glazes can be adjusted to achieve specific finishes and optimize the functional characteristics of the parts.
