Learning Pottery: The 50 Most Important Technical Terms for Beginners (Glossary)

Hardly any hobby is as full of technical terms as pottery. In your first class, words like leather-hard, grog, crazing or cone 6 come flying at you, often without anyone taking the time to explain them.

Every day, we at Formwerk Töpferbedarf Berlin advise beginners who face the same problem. They want to shop, pick a kiln or understand a glaze, and hit a technical term in every other sentence. This glossary is our answer: 50 key pottery terms, sorted alphabetically, explained clearly and briefly. 

A

Trimming. Finishing a piece that was formed on the pottery wheel. Once the clay is leather-hard, the piece is placed back on the wheel upside down and excess clay is removed from the bottom with a loop tool. The result: a clean foot, even wall thickness and a light, elegant shape. Without trimming, many thrown pieces look clunky at the bottom. You will find suitable loop tools and trimming tools in our tool selection.

Trimming on the pottery wheel

Hand building. Umbrella term for all pottery techniques that do not use a wheel. Classic examples are coil building, slab building and pinch pot technique. Hand building is the oldest pottery technique in human history; the wheel came much later. For beginners it is often the better start compared with throwing, because you have a finished piece in your hands sooner.

Overglaze color. Color that is applied after the glaze firing onto the already finished, glazed surface and fixed in a third, lower firing (usually 750 to 850 °C). It allows very fine, precise painting and is classic for porcelain decoration. The downside: overglaze colors are not as scratch-resistant as colors under the glaze.

B

Biscuit firing. Synonym for bisque firing, the first firing, in which the clay is turned into a hard but still porous body. Also called raw firing, glow firing or pre-firing. It usually takes place between 900 and 1,000 °C. Details and costs in our article What Is a Bisque Firing?

Firing schedule. The temperature curve over time during a firing, usually shown in a diagram: heating up, hold, cooling down. A well-programmed firing schedule is one of the most important factors for consistent results. Modern kiln controllers like the Bentrup TC66 store several schedules and make programming much easier.

The TC66 electronic controller from Bentrup.

Kiln shelf. Refractory shelf on which the pieces sit in the kiln. It usually consists of temperature-resistant ceramic materials and needs to be coated regularly with kiln wash (see there) so that glaze that has run does not damage the shelf. You will find suitable kiln shelves, kiln posts and kiln wash in our accessories section.

C

Cone. A small ceramic cone that melts down at a defined temperature. Originally developed to monitor a firing without a thermometer. Today mostly used as a temperature indication: Cone 04 = 1,063 °C (bisque firing), Cone 5 = 1,186 °C, Cone 6 = 1,222 °C, Cone 10 = 1,305 °C (high fire). You will find the full table in our article Pyrometric Cone Values.

Depending on the temperature, the cones melt differently and help the potter better follow how the temperature develops.

D

Pinch pot technique. Perhaps the simplest hand building technique. A small bowl is formed from a ball of clay simply by pressing in your thumb. Classically the first exercise in many pottery classes, because it works without tools and gives you a direct feel for the material.

Pottery wheel. A rotating disc for shaping clay. It comes in two versions: the manual kick wheel (driven with the foot) and the electric wheel (with foot pedal). For beginners, an electric wheel is almost always recommended, since the power is easier to control. For detailed buying advice, see Buying a Pottery Wheel: Which One Fits Your Way of Working?, and for the current models see our pottery wheel selection.

E

Single firing. A less common alternative to the classic two-firing method. The clay is glazed directly and fired only once to final temperature. It saves energy and time but is technically demanding. The glaze layer must be matched exactly to the state of the clay, otherwise it flakes off during heating. Not recommended for beginners.

Engobe. Colored clay slip that is applied to leather-hard or dry clay and fuses firmly with the clay body during firing. Unlike glaze, the surface of an engobe stays matte and slightly porous. It is excellent for painting, patterns and lettering. Often covered with a clear glaze to make it waterproof. 

F

Refractoriness. The property of a material to withstand high temperatures without deforming, melting or decomposing. Refractory items include, for example, the lining of the kiln, kiln shelves and kiln posts. For the clay body itself, the higher the temperature at which the clay sinters (see Sintering), the more refractory it is.

Flow. Describes how a glaze behaves during firing: how much does it run? Very fluid, i.e. flowing glazes such as many of the AMACO Potter's Choice glazes create dramatic drip and depth effects, but they need to be kept back from the bottom edge of the piece so they do not run onto the kiln shelf. Not to be confused with the chemical meaning of flux in glaze recipes.

Frit. Pre-melted, resolidified raw glass material that serves as the base in many glazes. Frits are chemically more stable and less toxic than the individual raw materials they are made from. That is why many modern glazes are frit-based. Not directly relevant for beginners, but the term often appears in glaze recipes.

G

Glaze. A thin, glassy layer that is applied to the bisque-fired body and melted in the glaze firing. It makes ceramics waterproof, hygienic and decorative. It comes in countless formulations: matte, glossy, transparent, opaque, reactive. A good introduction to the basics is our article Understanding Glazes: Types, Application and Common Mistakes. You will find all the glazes we offer in our glaze selection.

Glazes are usually liquid and applied with a brush as a brushing glaze. Here as an example the Iron Yellow glaze from the US manufacturer Amaco.

Glaze firing. The second firing after the bisque firing. Depending on the clay and glaze, it takes place between 1,040 and 1,280 °C. In this phase the glaze melts and bonds firmly with the clay body. Unlike in the bisque firing, pieces must not touch each other; glaze that has stuck pieces together cannot be repaired.

Greenware. Unfired, dry or semi-dry clay that has not yet been through the kiln. Extremely fragile. One small knock and the piece is gone. So always carry greenware carefully and never let it get wet, otherwise the clay dissolves again.

H

Hold (soak). The time during which the target temperature is held constant during firing, usually 10 to 30 minutes at the end of the heating phase. It makes sure the heat spreads evenly in the kiln and that all pieces are truly fired through. Without a hold, the center of the kiln often fires differently from the edge.

Hand building. Umbrella term for all techniques in which the clay is formed without a wheel, i.e. coil building, slab building and pinch pot technique. Hand building is more beginner-friendly than the wheel, allows organic, individual shapes and needs no expensive equipment. Many professional studios work exclusively with hand building.

I

Earthenware. Ceramics fired at low temperatures (900 to 1,100 °C). The body stays porous and is only waterproof with glaze. Classic for flower pots, Mediterranean terracotta and historic everyday ceramics. Not frost-proof: earthenware pots left outside in winter almost always crack.

K

Kaolin. Pure, white-firing clay mineral, the main component of porcelain. Kaolin has low plasticity (it is hard to shape) but is extremely refractory (can be fired above 1,400 °C) and provides the characteristic white base color. The name comes from the Chinese mountain Gaoling, where kaolin was first found.

Wedging. Preparing the clay before work. Goal: remove air bubbles, distribute moisture evenly and make the clay supple again. More important than many think; poorly wedged clay can burst in the firing. The classic spiral wedging technique is reminiscent of kneading bread dough.

Bone dry. The state of clay in which it is completely dried, like an old, bleached bone. No moisture left, no plastic deformability. Only in this state may the clay go into the bisque firing, otherwise it bursts from evaporating residual moisture. How long this takes is explained in our article How Many Days Should Clay Dry Before Firing?

Crazing. A fine network of cracks in the glaze caused by different expansion behavior of the clay body and the glaze. It can be a flaw (on functional ware crazing is unhygienic because bacteria get in) or an intentional design feature (classic in raku and Hagi ceramics). Some potters rub ink into the crazing to emphasize it.

L

Layering. Stacking several glazes on top of each other to create complex color and flow effects. Especially popular with the AMACO Potter's Choice series, which was developed specifically for layering combinations. Basic rule: apply the bottom layer in 2 coats and the top layer in 1 to 2 coats, and apply the top glaze thinner on the upper third. Explained in our AMACO Potter's Choice Guide, with all 70 colors in our glaze selection.

Leather hard. The state of clay between freshly formed and bone dry. Firm enough for the piece to hold its shape, but still damp enough to carve, paint or attach handles. The most important working stage for hand building and finishing. You can recognize leather hard clay by the fact that it feels cool and a fingernail leaves a slight mark when pressed into it.

M

Loop tool. A loop-shaped metal tool with a wooden or plastic handle, used to remove clay. Especially useful for trimming on the wheel or for carving out forms in hand building. Available in different sizes and shapes: round, oval, pointed, straight. One of the most used tools in every pottery studio. You can find more tools in our article The 30 Most Important Pottery Tools, and matching loop tools in our tool selection.

O

Oxidation (oxidation firing). Firing in an oxygen-rich atmosphere, as in any ordinary electric kiln. Metal oxides in clay and glaze keep their high oxidation state: iron appears brownish yellow, copper greenish. The opposite is reduction (see there). Almost all hobby potters work with oxidation firing, because it happens automatically in an electric kiln. You can find our range of electric kilns from Kittec and Pyrotec in the shop.

P

Slab building. A hand building technique in which clay is rolled out into even slabs and then joined into forms. Ideal for geometric objects: angular vases, bowls, tiles, boxes. The slabs are usually joined at the leather hard stage, glued with slip and scored cleanly along the edges so the joint holds.

Porosity. The share of open pores in the fired clay body. You can see it in how much water a piece absorbs. After bisque firing, porosity is high (which is why the body soaks up glaze). After glaze firing at high temperatures, a stoneware body is almost dense, with a water absorption of under 3 %. Earthenware always stays porous.

Porcelain. The finest and highest-firing type of ceramic, made mainly from kaolin, feldspar and quartz. Fired at 1,280 to 1,450 °C, it is white, dense and translucent. Demanding to work with, because it has little plasticity and is prone to cracking. Not the best starting point for beginners.

R

Raku. A Japanese firing technique in which the glowing piece is taken straight out of the kiln and placed in sawdust or straw. The removed oxygen and the thermal shock create unmistakable crackle patterns and deep black reduction surfaces. Historically closely tied to the Japanese tea ceremony. Details in our article Raku Pottery: What Is It?

Example of a cup fired using the raku firing technique.

Reduction (reduction firing). Firing in a low-oxygen atmosphere, only possible in gas or wood kilns. In the final phase the oxygen supply is deliberately restricted, so that metal oxides in the glaze release oxygen. As a result, iron turns deep red or black, and copper appears red or purple. Classic for tenmoku, celadon and oxblood glazes. Some modern glaze series such as AMACO Potter's Choice reproduce this look chemically, without true reduction. This is then called reduction effects in oxidation.

Raw ware. Unfired, dried clay, so a synonym for greenware. Some studios make a finer distinction: greenware is completely fresh and still damp, while raw ware is dry before firing. In everyday use, the two terms are often used interchangeably.

S

Grog. Fired, ground clay used as an additive in clay bodies. It increases stability (pieces hold their shape better), reduces shrinkage and cracking, and gives the clay more tooth. It is classified by particle size: from fine (0 to 0.2 mm) to coarse (0.5 to 2 mm). Grogged clays are the first choice for large pieces, hand building and anyone who likes a textured surface. You can find various grogged clays in our pottery clay selection.

Clay body. The fired clay form itself. Not to be confused with a “shard” in the sense of a broken fragment. Potters say “the body is dense” (meaning: well fired) or “a white body” (meaning: light-colored stoneware). The technical term therefore refers to the material after firing, not to something broken.

Slip. Clay mixed to a thin, liquid consistency with a high water content. It is used in several contexts: to join leather hard clay parts (attaching handles, joining slabs), as casting material for plaster molds (slip casting), or as a colored suspension for painting (then called engobe).

Bisque firing. The first firing. Turns dried clay into a solid but still porous body that can be glazed later. Usually between 900 and 1,000 °C. Also called biscuit firing, raw firing or pre-firing. 

Sintering (sinter). The process in which clay particles bond together at high temperatures without melting completely. The result is a dense, hard clay body. Stoneware and porcelain are fired beyond the sintering point, which is why they are watertight. Earthenware is fired below it and stays porous.

White earthenware. Ceramic fired at low to medium temperatures (1,050 to 1,150 °C) with a porous, white or light-colored body. Only watertight with glaze, otherwise similar to earthenware. Classic for everyday tableware and mid-priced tiles. Despite the similar-sounding German names (Steingut and Steinzeug), it is ceramically far removed from stoneware (see below).

Stoneware. Ceramic fired at high temperatures (1,200 to 1,300 °C) with a dense, sintered body. Watertight even without glaze, very sturdy, frost-proof. The classic choice for functional tableware from studios and workshops, from coffee mugs to salad bowls. 

T

Terracotta. Italian for “baked earth.” Refers to unglazed, red-firing earthenware, classically Mediterranean flower pots, amphorae and historical sculptures. Porous body, reddish brown color (due to high iron content), not watertight. To make it watertight, terracotta is often coated with a slip suspension and fired slightly higher.

Clay. The raw material of pottery. Chemically, a fine-grained sedimentary rock made of layered silicates that becomes plastic and shapeable with water. There are hundreds of different clays with different properties: firing temperature, color, plasticity, grog content. For beginners we recommend grogged stoneware as a versatile all-rounder. You can find our complete range in the pottery clay selection.

Pottery wheel. A synonym for potter's wheel, the rotating tool for shaping clay. Some people use one term for the classic, hand-operated version and the other for the modern electric one. In practice, the terms are used largely interchangeably. Current models in the pottery wheel selection.

Kiln wash. A refractory coating, usually a mixture of alumina and kaolin, applied to kiln shelves so that glaze that has run doesn't stick to the shelf. Also called shelf release or kiln shelf wash. It needs to be renewed regularly once the layer shows cracks or flakes off. You'll find suitable kiln wash and spare parts in our accessories section.

U

Underglaze. Color that is applied to the bisque-fired body and then covered with a clear glaze. It is fired in during the glaze firing. Result: the color sits protected under the glaze, is extremely scratch-resistant and food-safe. A classic choice for painted functional ware, because it is durable and dishwasher-safe.

W

Wabi-sabi. A Japanese aesthetic concept that recognizes beauty in the imperfect, the impermanent and the simple. In ceramics, this shows in asymmetrical forms, visible fingerprints, broken glazes and firing marks, features that make a piece unique. 

Coil building. A hand building technique in which clay is rolled into even ropes (“coils”) and stacked layer by layer. After each layer, the joins are smoothed so that a continuous vessel is formed. One of humanity's oldest pottery techniques and ideal for round vessels, vases and bowls without a pottery wheel.

Z

Centering. The first and most important step when throwing on the pottery wheel: the clay is pressed and shaped on the wheel so that it rotates exactly in the middle. Without perfect centering nothing else works: the clay wobbles, the walls become uneven, the piece tears. Centering is the first big hurdle every beginner has to overcome. Many classes devote an entire first session to centering.

Intermediate firing. An additional, often third firing between bisque firing and glaze firing, for example after applying an engobe that needs to be set again before glazing. Not necessary for every project, but can make sense for complex decorating techniques. It increases time and energy use, but gives maximum creative freedom.

Frequently asked questions

What is the difference between clay and ceramics?
Clay is the raw material, the damp, plastic material that pieces are formed from. Ceramic is what it becomes once it is fired. As soon as you put your dried clay piece in the kiln and it hardens, the clay turns into ceramic, and irreversibly so.

What exactly does leather hard mean?
Leather hard is the state between freshly formed and completely dry. The clay holds its shape but still feels cool and damp. Pressing with a fingernail leaves a slight mark. In this state you can carve your piece, work it with tools, attach handles or paint it with engobe.

What is the difference between glaze and engobe?
Both are applied to the clay, but they work differently. Engobe is a colored clay suspension. It stays matte and slightly rough and is usually applied to leather hard clay. Glaze is a glass-like coating. It melts during firing and turns glossy or matte, and is usually applied to bisque-fired ware. The two can also be combined.

Why is ceramic fired twice?
The first firing (bisque firing) makes the clay hard, but still porous. This matters so the glaze adheres properly in the second firing. If the body were already dense, the glaze would flake off. Two firings are the classic, forgiving way. Covered in detail in Can You Fire Ceramics Twice?

 

Conclusion: Vocabulary as a Tool

Pottery terms can seem like an unnecessary hurdle at first glance, as if the craft had been made mysterious on purpose. In truth, though, most of the terms are simply craft vocabulary: precise names for states, techniques and materials that also need to be told apart precisely. Once you understand them, you can communicate in any studio in the world.

This glossary covers the core terms you will come across in classes, specialist literature and online forums. If you want to go deeper, you will find dedicated articles on many of the terms in our blog, and we have added the matching link in almost every entry.

If you are just starting out and wonder what you actually need to pot at home, we recommend our article How Expensive Is Pottery as a Hobby? as a starting point. You can get going right away with our complete range, which covers everything from clay to tools and glazes to kilns. And if questions remain, just get in touch, we are happy to advise you.

Note: This glossary is meant as a practical introduction and makes no claim to academic completeness. Technical terms evolve with practice, and regional differences in naming are possible. For more in-depth definitions, we recommend the Keramikinstitut glossary as a complementary source.

Happy pottery making, the Formwerk Berlin Team