Ceramic - Pottery Dictionary

by Susan Mussi

ca: RAKU

es: RAKU

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*Raku,*is an oriental technique dating back to the 16th century. It is believed to have originated in Korea but it prospered in Japan and has extended throughout the world, it was originally created for the tea ceremony. The word Raku means “happiness”. It is a method of creating effects with colors and textures either by the use of enamels or simply with smoke, it involves rapid firing and rapid cooling while still red hot from the kiln. The clay used for Raku must be prepared with a high percentage of sand or grog to withstand the rapid and extreme changes of temperature. The clay to be used should be chosen with care to avoid the risk of breakage.

The firing of the enamels is done in gas or wood fired kilns. Raku enamels and colors are fired from 800º to 1000º C with a rapid firingx to reach the right temperature in 15 to 30 minutes, then the kiln is opened and the red hot piece is taken out.

The piece is taken out of the kiln and exposed to the air then put into a metal bucket half full of sand or dry leaves for a short while, just long enough for the reduction and the smoke to penetrate into the piece, transforming the colors and enhancing the crackled enamel effect produced by the heat crash, a common characteristic of this enamel technique. Next it is rapidly cooled down in another bucket full of water and the smoke stuck to the enamel is washed off at the same time.
Besides the finishes achieved with classic enamels, both shiny and crackled, we also have the naked or lost enamel Raku technique, whereby an engobe that does not bond well to the piece is used, causing the enamel to come off at the end of the process leaving only the patterns made by the smoke. The patterns can be left to chance (crackled) or designed by the ceramist.

Another technique is known as the “matt copper” technique. By using an enamel supersaturated with copper, we can achieve a matt finish together with the wide range of colors that copper develops in a reducing atmosphere.

The kiln can be loaded from the top or from the front, although the most recommended type is the one designed so that the body of the kiln is lifted up by pulleys and the fired pieces remain on the floor and so are easy to handle. This procedure produces smoke, so it must be done in the open air. To get the pieces out of the oven you must use long tongs and protect yourself with protective glasses and heatproof gloves.

Link to Author – Ramón Fort



Raku tongs are specially designed with long steel handles and legs. They are used to lift red-hot work out of the kiln and move it to the metal bucket of sand. The length allows you to hold the piece securely, far from your body and from the kiln, which emits very strong smoke and heat when opened.

ca: CRU


Raw applies to materials used by potters that have not been fired, such as raw clay, raw slip or glaze. It also defines clay when taken from the earth, before being processed by crushing and sieving to remove stones and give it a smooth, plastic pliability.



Raw material (clay) is a natural product that is found in the earth and that has been prepared to use but not fired.



Raw ware is clay prepared but not fired. The glaze can be applied to the clay during the different stages of drying and it can be decorated with slips and glazes that are applied by dipping, pouring, spraying etc. It then becomes decorated raw ware.



Reabsorption of vapor refers to the dampness absorbed by clay from the air. The quantity depends on the dampness of the atmosphere, which can change from day to day and room to room. Clay can accept these adjustments, but when completely dry, if it reabsorbs moisture, this will cause a slight expansion. Some parts are finer than others and reabsorb dampness quicker than the thicker parts this makes a tension between different thicknesses and can cause cracking or breaking.

Re-absorption of water refers to water being added to dry clay, so as to make it more pliable


es: ROJO

Red is a strong color with many tones. There is a large selection of reds used in different types of decoration, which are fired at different temperatures. In the past it always had to be fired at a low temperature, between 700 and 800º C. This meant if working with colors fired at a higher temperature, the piece with red had to be fired a second time at a lower heat. In the last years this has changed, now it can be bought to use at different temperatures.



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The name of a restaurant made in flat relief, shown above, is made in twelve parts that form three sections and each one is decorated differently.

a) The top part is in six separated pieces of flat relief; Nº1 to Nº6. The figure and food are 1cm higher than the background. Pieces 1 & 5 are high, 2 & 6 low and 3 & 4 are one piece but on two levels, the design and background.
b) It is decorated using the Dry-Cord method for the three colors red, orange and white, the white being the glaze-base for “Siglo 18”. The centerpieces were covered with the base by throwing; the outlines were scraped off and filled with red. The background orange was dripped on, leaving the outer border, which was then drawn on with pencil and the spaces filled up with the appropriate colors, red and white.
c) In the middle section is “El Portalet”, the name of a restaurant which is in three pieces, the letters are higher and both the white and red background were dripped on.
d) The three pieces at the bottom are flat, the outlines of the letters were drawn on paper, marked on using carbon paper and both colors were dripped on, white glaze-base for the letters and red for the background. To avoid the colors from touching each other when painted, they were cleaned by putting a very thin piece of wood between them along the outlines, then the rough edges were smoothed down with a soft paint brush and clean water.
Read more about: Dry cord / Dry cord 1 / Dry cord 2 / Dry cord 3



Red clay is earthenware clay of different shades of brown, due to the iron oxide in the earth where it is found. It has to be processed before being used and can be bisque fired between 850º C and 1050º C.



Red hot is the color the kiln reaches between temperatures of 700º C and 800º C. It acquires a red glow, which increases as the temperature becomes higher. With practice, by looking at the color, you can judge the state of the firing and how much longer it will need.



Iron oxide: also known as ferric oxide, hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust—is one of the several oxide compounds of iron, and has paramagnetic properties. Its chemical formula is Fe2O3.



Reduction is when something is made (smaller / or shrinks) or is reduced, decreasing the size, price or quantity.

Reduction (Deoxidation) takes place in the firing of ceramics with gas or wood. The oxygen in the kiln is reduces and / or eliminated, combustion js create and the smoke that is produced, that contains particles of carbon or carbon monoxide. These particles lodge in the pieces (except where there are reservations) and alter the colors.
The exception is the Raku pottery, where the reduction takes place outside the kiln while the piece is still is red hot.



Refractory coatings have many different names; bat wash, flint wash, etc. They are generally used to cover kiln shelves to protect them from clays which if over-fired can disintegrate and from slips and glazes that can run and when cold form an adhesive that sticks to the walls and work.



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Repeated tiles are designs on tiles made up to form a repeated pattern and the designs can be of one or more tiles put together to form a continued design.
In Spain they have been used through many centuries. The photos below show four different designs we have reproduced for the restoration of old buildings.
a) The first photo is a balcony in Barcelona and to restore it the tiles were made copying as closely as possible the old classical Catalan designs size 13×13cm,the texture of the glaze-base and colors.
b) and c) are the tiles used in the balcony.
d) This is designed to be used as a border 20×20cm to go round the bottom part of a wall, made at the beginning of the last century.
e) A repeated one tile design 15×15cm, 16 tiles are shown to illustrate the two patterns one design can create.
f) A classical design 13×13cm showing an old lamp.

Note: All the tiles shown here are decorated using the Majolica, on-glaze method. When a design has to be repeated many times the outlines are screen printed, then all the colors are hand painted. With designs of one tile that is repeated and placed side by side to form a pattern, it is very important that the lines that go to the edges coincide. So when one tile is laid next to another the lines of the drawing meet.

Link to Ceramics Bensu for Repetition-Tiles decorated with the Majolica Method Repetition-tiles

Read more about: Screen Printing / Architectural Ceramics / Majolica: 5a – Preparing to paint tiles, plates, jars and lids

ca: RAJOLES REPETIDES – Marcar un disseny.

es: AZULEJOS REPETIDOS - Hacer un diseño

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Repeated designs on tiles. Here is explained creating a design for only one tile, it is the same if there are more than one.

How to copy an antique design or make a new one.

Working with your computer, use a photo or scan the design you want, Keep only the outlines and remove all the colors. Open another file and draw the exact measurement of the outlines of tile, copy the design on to it and fit it in.

Now cut it in half diagonally, remove one half, copy and flip over the one that is left and join them in the middle. It is very important to do this on a large scale so you can see all the lines connect exactly. Now copy it and move the copy round, checking that the lines of the design connect correctly.

When finished print it onto transparent paper, check it for size against a tile and if there is room on the paper wright its name, code, size, and F for face so when you use it you know which way round it has to be. Now you can pounce it and paint it by hand using the Majolica Method, cut and prepare paper for stenciling or have it mounted for screen printing.

When reproducing old tile designs, copy it as much as possible, to make a true likeness to the original, in size, texture and colors. One of the problems is that many old designs have been copied and printed industrially or with screen printing and if printed it is impossible to reproduce them by hand, as when hand painted two tiles are never exactly the same.

The only part of a hand painted design that can be done by screen printing is the outlines all the colors have to done by hand. Reproduction of antique tiles decorated by hand that have been reproduced by screen printing leave the colors flat and exactly the same on every tile and hand painting shows the movement of the brush storks, which give different intensities to a color.

With the method photo-ceramics reproduction of tile designs can be made exactly the same as the original as long as they have no relief texture in the surface.

Note; Screen printing has seven sections that explains using it with the Majolica method to print outlines. This is a link to the first and they are in the order of working. Read more about: Screen printing (0) The ways of working



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Repoussé, the dictionary explanation is: “A design raised in relief by hammering out on the reverse side.” It is a French word meaning “pushed up”. The word also applies to a design in three dimensions but in reverse, pushed inwards not outwards. When using clay, it can either be built up or dug out so the design is inwards, but with marble the design has to be carved out.

The photo above shows a work in Barcelona by Josep Mª Subirachs, a well-known Catalan sculptor who is now actually working to finish Gaudi’s “Sagrada Familia”. It is carved in marble; all the design protrudes outwards except the face, which is carved inwards so all the features are indented. It is only when you are up close that you realize this, as when you are far away you have the optical illusion that it is done in the same way as the rest of the design.

ca: LLENGÜETA de ronyo

es: LENGÜETA de riñon

Ribs are ceramic tools made of plastic, wood, metal and rubber and are used to smooth clay while turning with a wheel. They have this name because originally animal bones were used to make them. There are several sizes and two types ridged and flexible.
In English they are also known as kidneys as some have the shape of a human kidney. In Spanish and Catalan the word tongue is used in both languages; in Spanish lengueta and in Catalan llengüeta.
Read more about: Kidney



Riddle is another name for mesh; interwoven threads in different materials, that form square holes of different sizes. Used to separate and clean materials, such as clay, crushed bisque, colors, etc.

ca: ROTLLO DENTAT – decoració en argila

es: ROLLO DENTADO – decoración en arcilla

Rolled clay decoration refers toipatterns or textures indented into the surface of soft clay using a roulette wheel. This is explained in Impressing



Rolling pin is a cooking tool used for rolling out pastry and in ceramics, for rolling out clay. The clay is put between two walls or square poles of the same height. The height of the poles is the height you want your clay to be. Roll over the clay until the rolling pin rests on the walls, it will then be the height required.
Read more about: Slab – Slabbing with a rolling-pin



Roof tiles are ceramic products made of fired clay or slate to put on the top of buildings to keep out rain. There is a large variety, they are thin, parallel, of different widths and lengths and bent to form different shapes.



Rotary sieve; made in metal with all its parts dismountable. It has changeable floors of disks with different sized mesh. It has two handles, one overlaps the wall on both sides and at one end is the handle to pick it up with, both are attached with screws to the wall and in the middle there is a hole which the second handle goes through and is attached to the brush. When turned it rotates a brush over the mesh and pushes the substances, liquid or powders through the mesh.

a) The wall. b) The different sized disks, which make up the floor. c) The handle to hold and turn the brush. d) The brush. e) The handle to turn it. f) The first three pieces together. g) The last three pieces together. h) The complete rotary sieve.

Read more about : Glaze-base (c) Preparing the glaze-base at the end it has a video where you can see the rotary sieve being used.



Rough is when a surface is coarse, rough or uneven and in ceramics can be accidental or designed.



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Roulette Wheels – Roller Tools – They are known by these two names in English.
Handmade. It is a cube of wood or bisque made with a pattern notched into it. It can be of any size and be attached to a handle. When rolled over soft clay, the protruding parts are indented into the clay to create a pattern or texture. If you make a roulette wheel using clay, after creating the pattern, leave it to dry. When dry it can be used, but if it is to be used frequently fire it, as the dampness of the clay you will be working on will affect it. If a handle is required, build up the clay round a tube length-wise, so it goes through the middle. It should be big enough to pass a small pole of wood or metal through, which can then be attached to a handle. This makes it easier to roll and imprint. A good idea is to make a detachable handle, which can be used with all your designs.

Industrially made. They many different types of roller tools, in shapes, sizes and the materials they are made of. The ones in the following photos are made with hard wood that has been prepared to be durable against dampness. It is in two parts the handle and roller, the rollers are made with different sizes in length, diameter and designs to use with the same handle, the smallest 0.5 cm and the largest is 6,0.cm and each size has a large selection of different stamp designs. The following photos show how to use them.

Go to Impressing and enlarge the first photo. It shows some that are completely handmade and very practical, designed with one piece of thin metal that is bent. At the top it has a ring to hang it up, in the middle a space to hold it while working and with a roulette wheel hooked at the bottom end.

Read more about: Impressing / Impressing stamp



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Ruler is a strip of wood, metal or plastic with straight edges that are usually marked with whole and fractional units of length, inches, centimeters or both and used to draw straight lines and measure lengths. Rulers are made in different lengths, from ten centimeters to five meters and in one piece or many pieces hinged together to fold up. The illustrations show three types.

a) The ruler is 1 meter long and in four sections of 25 cm.
b) One side section of a) opened to show the center disk. It can be opened to 180º and each of the two sections on the left and right are connected and are opened by a hinge.
c) Metal ruler.
d) Plastic ruler.

Note: When made in a pliable material that can be bent and rolled up, it is known as a tape measure.

ca: FUNCIONAR - Amb relació a un fluït

es: FUNCIONAR - Con relación a un líquido

a) Run: a paint brush runs when it makes a nice long stroke.
b) Run: color runs well when it flows smoothly off the paintbrush.