Ceramics Glossary
Find definitions for ceramic terms, materials, techniques, and tools.
Discover glossary terms
Potassium feldspar (KAlSi₃O₈)Potassium feldspar is an essential mineral in ceramics, used as a flux in glazes and clays. Its high potassium content lowers the melting point of ceramic mixtures, facilitating vitrification at lower temperatures. This improves the efficiency of the process and the quality of the finish, creating smooth and shiny surfaces, especially in fine ceramics such as porcelain.
In addition to its function as a flux, potassium feldspar improves the thermal stability of ceramic pieces, helping them resist temperature changes without warping or cracking. This makes it a key component in high-end ceramics, and in industrial products that require durability and thermal resistance.
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.
Tobikanna or chatteringTobikanna, also called chattering, is a traditional Japanese decorative technique used to create unique textures and patterns on the surface of ceramic pieces during throwing. This technique involves the use of a metal tool with spikes, which scrapes the surface of the clay as the piece is throwed on the pottery wheel, generating a texture of crisscrossing lines or irregular patterns that add depth and character to the piece.
The marks left by the tobikanna are not only visually appealing, but also add a tactile texture that enriches the sensory experience of the piece. In addition to its decorative function, tobikanna can enhance the adhesion of the glaze to the surface of the clay by creating micro-textures that facilitate the attachment of the glaze coating.
Screen printing screen or silk screenA silk screen is a tool composed of a frame on which a fine mesh, traditionally made of silk or nowadays of nylon or polyester, is stretched. This mesh contains areas that are permeable and impermeable to the passage of ink or ceramic engobe. By pressing the coloring medium with a squeegee through the mesh, the design is transferred to the surface of the piece, whether it is a tile, plate, cup or any other ceramic object.
Screen printing makes it possible to reproduce complex designs, repetitive patterns or even detailed illustrations with high precision. This is especially useful in the industrial or semi-craft production of tableware, tiles and decorative pieces, as it ensures uniformity, consistency and speed in decoration.
Sodium carbonate (Na₂CO₃)Sodium carbonate, also known as soda, is used as a flux in ceramics to reduce the melting temperature of glazes and improve their transparency. This compound is essential in the formulation of low-temperature glazes and earthenware, when a glossy and smooth glaze finish is desired.
In addition, sodium carbonate helps to improve the fluidity of the glaze during firing, which facilitates a uniform application on the ceramic piece. It is also used in atmospheric firing techniques, such as sodium firing, where it is introduced into the kiln to create textured effects and chemical reactions on the surface, achieving natural color effects and unique finishes.
HidasukiHidasuki is a Japanese decorative technique that generates reddish or orange patterns on the surface of ceramic pieces, usually made with Bizen clay. This unique effect is achieved by wrapping the pieces with straw strings before firing. During the firing process in a kiln, the strings are burned and their ashes react chemically with the minerals in the clay, leaving characteristic marks in the form of lines or stains.
Hidasuki is a direct expression of the interaction between natural materials and fire. Because the patterns are unpredictable and depend on factors such as kiln placement and flame intensity, each piece is completely unique. This approach celebrates partial control and acceptance of spontaneous results, fundamental characteristics of Japanese ceramics.
PorosityPorosity is the property that determines the capacity of a piece to absorb liquids, due to the presence of small pores in its structure. This characteristic is directly influenced by the firing temperature and the degree of vitrification reached during the manufacturing process. Firing at lower temperatures results in more porous pieces, since the clay or glaze is not completely vitrified, allowing liquids to penetrate through the pores. Conversely, higher temperatures favor complete vitrification, significantly reducing porosity and making the piece less absorbent and impermeable.
For example, earthenware, fired at relatively low temperatures, tends to be porous and often requires an additional coating to make it impermeable, while stoneware and porcelain, fired at high temperatures, are naturally impermeable and suitable for the manufacture of tableware and utensils that come into contact with food and beverages. On the other hand, terracotta, with its high porosity, is ideal for pots, as it allows water and air to circulate, preventing waterlogging of plant roots.
Gerstley borateGerstley borate is a natural material that has been used for decades in ceramics as a flux in low-temperature glazes. Its boron- and calcium-rich composition allows it to lower the melting point of glazes, which facilitates the creation of vitrified and shiny surfaces in pieces fired at moderate temperatures. It is especially valued in transparent glazes and in combinations with metallic oxides to produce vibrant colors and unique decorative effects.
Gerstley borate also acts as a stabilizer that helps prevent problems such as run-off or cracking in glazes. In its natural state, Gerstley borate contains impurities that can contribute to unpredictable decorative effects, such as textures and color variations, making it a popular ingredient in artistic ceramics.
However, its limited availability and variations in its chemical composition have led to the search for modern alternatives, such as synthetic borate blends. Despite this, it remains a popular material in handmade ceramics, especially for decorative and experimental pieces.
Sodium feldspar (NaAlSi₃O₈)Sodium feldspar is a mineral used as a flux in the formulation of ceramic glazes and clays. This mineral is especially valuable because of its high sodium content, which helps lower the melting point of ceramic mixtures, allowing them to vitrify at lower temperatures. It also plays a role in the thermal resistance of the pieces, as it helps to reduce thermal expansion and improve dimensional stability during firing.
One of the most appreciated characteristics of sodium feldspar is its ability to contribute to the formation of a smooth, shiny and high quality surface in glazes.
Its use is especially prevalent in mass production ceramics, where energy efficiency and consistency in glaze quality are priorities. In these industrial applications, sodium feldspar helps ensure a more economical and controlled manufacturing process, making it possible to produce large volumes of ceramics without compromising the quality or durability of the pieces.
Arabic gum and tragacanth gumArabic gum and gum tragacanth are natural, water-soluble gums used in ceramics to act as binders, stabilizers and thickeners in the preparation of glazes, engobes and pigments. When mixed with water and ceramic colorants, these gums improve the adherence of the particles to the surface of the piece, preventing them from spalling during the stages prior to firing. Their use is particularly valuable in decorative techniques such as fine brushing, the application of decals and the elaboration of hand-painted details on the raw or bisque fired surface.
Gum Arabic, extracted from various species of acacia, is known to be more fluid and easily handled. Its main virtue is to improve pigment fixation, ensuring uniform application and preventing particles from dispersing. Gum tragacanth, obtained from species of the genus Astragalus, generates a more viscous and stable mixture, useful when greater density, application control or thicker layers of material are required.
