Ceramics Glossary
Find definitions for ceramic terms, materials, techniques, and tools.
Discover glossary terms
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.
SpallingSpalling is a ceramic defect that occurs when the glaze or engobe detaches from the clay body in small fragments or flakes. This problem is mainly caused by compressive stresses in the glaze layer, caused by an incompatibility between the coefficient of thermal expansion of the glaze and that of the clay body. These stresses, if too high, exceed the strength of the glaze, causing it to separate.
This defect affects both the aesthetics and the functionality of the pieces, especially in utilitarian objects such as tableware or liquid containers, where spalling can compromise the impermeability. For example, a cup with spalled glaze on the inside not only loses its visual appeal, but can also absorb liquids, becoming unusable or unsanitary.
To prevent spalling, it is essential to ensure thermal compatibility between the glaze and the clay body, apply the glaze in uniform layers and avoid firing cycles with abrupt temperature changes. Also, a correct preparation of the surface of the piece, free of dust or grease before glazing, improves adhesion and reduces the risk of this defect.
Bas-reliefBas-relief is a sculpting technique applied to ceramics that consists of creating slightly protruding decorations on the surface of the piece, in contrast to high relief where the elements protrude significantly. In bas-relief, the figures or patterns have a moderate depth that gives them a subtle but visible appearance, allowing the details to be appreciated from different angles. This technique is commonly used to add decorative embellishments, elaborate borders and geometric patterns, enriching the aesthetics of the piece without compromising its structural integrity.
Bas-relief allows the incorporation of decorative elements that add texture and complexity to the pieces, creating a balance between flat form and three-dimensional shapes. This technique can be used to depict a variety of subjects, from natural motifs such as flowers and leaves to abstract and geometric patterns. In addition, bas-relief can be combined with other decorative techniques, such as glazing and engobe painting, to achieve more elaborate and personalized finishes.
FinishingFinishing refers to the techniques and processes applied to a piece once it has been shaped and fired to enhance its aesthetic appearance and functionality. This process can include a variety of methods, such as glazing, painting, engraving, glazing and the application of textures. The finish is crucial in defining the final appearance of the ceramic piece, as it determines its color, gloss, texture and resistance to external factors such as wear and liquid absorption.
There are different types of finishes that can be applied depending on the style and purpose of the piece. For example, a gloss finish can provide a polished and professional appearance, while a matte finish can offer a more rustic and natural aesthetic. In addition, finishes can include additional decorative elements, such as reliefs, engravings or inlaid materials, which add depth and detail to ceramic pieces.
PaddlingPaddling is a ceramic modeling technique that consists of delicately striking a piece of clay with a flat tool, known as a palette, which can be made of wood, rubber or even metal. This process allows the shape, profile and surface of the piece to be modified without applying direct pressure with the hands, which facilitates the preservation of symmetry and control of volumes. Upon repeated impact, the trowel compacts, smoothes and molds the clay, creating more defined surfaces, subtle depressions or textures without altering the structural integrity of the piece.
PyrometerThe pyrometer is a fundamental instrument in the control of the thermal cycle of the kiln. Its main function is to convert temperature variations into numerical readings, allowing to adjust the heating curve, the holds (times at constant temperature) and the cooling process. Thanks to this precise control, the kiln's internal atmosphere can be adapted to the needs of the clay body and glazes used, whether it is an oxidizing, neutral or reducing atmosphere.
Throughout the thermal ascent, the pyrometer helps to avoid sudden temperature rises that could cause cracking or internal stresses in the pieces. Similarly, during cooling, proper monitoring reduces the risk of thermal shock. The use of the pyrometer in combination with other indicators, such as pyrometric cones or the color of the kiln interior, provides a complete picture of what is happening during firing, increasing the reproducibility of results and the final quality of the work.
Temperature/time factorThe temperature/time factor refers to the dynamic relationship between the temperature reached in the kiln and the time during which that temperature is maintained, or transitions are made between different stages of the firing cycle. It is not enough to reach a certain degree of heat; the duration for which the ceramic pieces remain at that temperature is equally decisive in achieving optimum body and glaze maturation.
Precise control of the temperature/time factor makes it possible to obtain shiny, stable and flawless glazes, as well as more resistant and less porous ceramic bodies. If the temperature is too high or maintained too long, deformations or drips may occur in the glaze; on the other hand, if it is insufficient or the time is too short, the result may be incomplete vitrification or dull and porous glazes.
Giffin GripThe Giffin Grip is an innovative tool designed to facilitate the centering and clamping of ceramic parts on the wheel during the trimming and finishing stages. It consists of a rotating disk with adjustable arms that expand or contract to hold parts of different sizes and shapes. This tool is especially useful for ceramists working in high production or in workshops where efficiency and precision are essential.
With the Giffin Grip, you can quickly center bisque or leather-consistency parts without the need for complex manual adjustments. This not only saves time, but also reduces the risk of damaging parts when handling them. Although it is a modern tool, the Giffin Grip is inspired by traditional centering techniques, adapting them to the contemporary needs of ceramic production.
Oxidation or oxidizing atmosphereOxidation in ceramics refers to a type of atmosphere during firing in which there is an abundant supply of oxygen. This environment is crucial for certain ceramics and glazes that depend on the presence of oxygen to develop bright, consistent colors and specific glaze properties. In an oxidizing atmosphere, the free oxygen in the kiln reacts with the glaze and clay components, preventing them from reducing (losing oxygen) and ensuring that the metal oxides maintain their original oxidation states.
In an oxidation kiln, precise control of the amount of oxygen is essential to achieve the desired results. For example, iron oxide in an oxidizing atmosphere tends to produce red, orange and brown colors, while in a reducing atmosphere it can produce dark green or black tones. This control is achieved by regulating air flow and combustion within the kiln, allowing the visual and physical properties of the parts to be manipulated.
In addition to influencing color, the oxidizing atmosphere affects the texture and finish of the glaze. Glazes applied in this environment tend to develop more uniform surfaces that are less prone to defects such as pullout or staining. This is particularly important in the production of utilitarian and decorative ceramics where aesthetics and functionality are paramount.
Glaze densityGlaze density is a crucial factor that significantly influences the final result of a piece. This measure refers to the concentration of solids present in the glaze suspension, i.e., the ratio of ingredients to water content. Glaze density directly affects aspects such as coverage, thickness and uniformity of the finish once the glaze has been fired in the kiln. A glaze with an adequate density will ensure uniform coverage without excess or deficiency, which is essential to achieve an aesthetic appearance and optimum functionality of the ceramic piece.
Incorrect density can cause various problems during firing. A glaze that is too dense can generate run-off, uneven build-up and bubbles, resulting in uneven finishes and structural defects. On the other hand, a glaze with low density may not adequately cover the piece, leaving exposed areas that not only affect the aesthetics but also the impermeability and durability of the ceramic. In addition, the density of the glaze can influence the way the glaze reacts with the clay and other components during firing, affecting the adhesion and resistance of the final finish.
