Gas: Physics; gas is a substance possessing perfect molecular mobility and the property of indefinite expansion, as opposed to a solid or liquid products. (Webster’s)
It expands and contracts with changes in pressure and temperature and spreads uniformly within a container, has a very strong smell and is very dangerous if it escapes; if it connects with fire it will cause an explosion and can kill if inhaled.
In ceramics there are gas kilns, which for large industries are the most economical. When firing using whatever type of kiln, fumes called gases are produced, some of which are very strong. These are not caused by using gas but by the burning of the products in the kiln; clay and transfers expel strong gases.
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es: HORNO DE GASClick on the title to see more images
1) Gas kiln: It is square, packed and opened from above. The lid is opened by pressing a pedal with your foot, and pulled outwards horizontally over two guides. It has two burners and the ventilating hood is on top of the kiln with a handle which allows the opening or closing of the entrance of air when firing is being reduced.
a) The kiln chimney. b) A sliding lid at the top, c) The gas controller. d) Nozzle to the gas burner with air ccontroller. e) A pedal at the bottom to open the sliding door at the top
2 – 3) Gas kiln: It is round and packed from above. The top part is a lid that has a ventilating hole and above it is the hood; they are separated but attached by a small metal bar on each side and it has two burners. The vent hole has a handle to open or close the entrance of air.
The lid can be lifted and moved horizontally by pressuring your foot on top of the pedal which is underneath the kiln
4) Gas kiln the system is the same as 2 & 3 and it is still fabricated.
5) Gas kiln: A square one with a door at the front, the burners are placed at two lateral parts of the kiln and there are three for each side, the chimney and a ventilating hood are attached to the top with a handle for opening and closing the entrance of air.
Note: When used the ventilating hood or chimney are connected to a tube that goes outside. It can have a suction fan to draw out and expel the combustion of toxic gas, fumes and odors that have been created during the firing.
These kilns are made to be controlled manually or automatically and usually their maximum temperature is 1300º C.
Gauge post is used for two purposes; to gauge lines round pots as decoration and to check that the different widths of a pot are correct all the way round. It is a pole which supports one or more arms and with a floor at the bottom that can be attached to a table. The arms and the pole are long and flat with a space in the middle and they are joined by a screw which allows the arms to be moved backwards and forwards, up and down and be put at different angles The ware is centered on the wheel and the base of the gauge is screwed to the table, the arms are set to the height and width needed, then turning the pot slowly, you can check that the shape is the same size all the way round.
ca: GIFFIN GRIP
es: GIFFIN GRIPClick on the title to see more images
The Giffin Grip is a tool made to be attached to a potter’s wheel. It is designed to hold plates and jar, when they are leather hard, upside down and correctly centered, while being turned. It holds the pieces in place while trimming the footings and it makes the work faster and easier. It is used for the same purposes as a chuck and comes in two pieces, a spiral plate which is a wheel bat, and a top plate which holds what is being turned.
The three illustrations show how to work with a large plate, jar and small plate. Click here Giffingrip there are two videos, the second gives instructions on how to mount and how to work a Giffin Grip.
Read more about: Chuck
Glaze in ceramics works as a varnish does for furniture, except that glazes have to be fired. In Spain it is called varnish and is a finely ground mixture of minerals and industrially made powders such as silica, alumina and flux, prepared to melt at different temperatures.
Glaze is bought prepared as a powder and is one of the most important products used in ceramics. Traditionally lead oxide was used, but this is now illegal due to health reasons. Tin oxide is currently the main ingredient for glazes, this product being developed for its whiteness and opacity. There are many different types of glaze-bases made up with different formulas and textures, matte, semi-matte and crackle, etc. and all can be purchased ready-made.
To use, it is mixed with water and laid over ware either in the clay or bisque state and when fired, it melts and turns into a transparent, thin, layer of glass that can be shiny or matte. The natural color of the bisque or clay reflects through the glaze giving it a strong, attractive quality. The glaze makes ceramic work non absorbent to liquid and the process is known as glaze firing.
It is mixed with products to form colors and glaze-bases that can be transparent, matte or opaque and can be applied by spraying, painting, burnishing, dipping, pouring, etc.
Crystalline glazes contain zinc and titanium oxides which cause the crystals to grow. When the heat is raised, the glaze becomes fluid and forms the distribution of the crystals on the pottery. If you have decorated the inside of a basin, all the crystals will fall to the centre and form a solid thin layer of coloured glass with the crystal effect inside it. For the inside of a basin there is no danger of the colours running, but for a pot or the outside of a basin precautions should be taken to ensure they do not run off and fuse into the kiln shelves.
Photos by Concha Martín Soriano
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es: FRITA DE ESMALTE
Glaze frit, glaze body frit. In the relationship between the thermal expansion of body and glaze, a glaze ideally should have an expansion that is slightly lower than the body so that contraction during cooling puts the glaze under compression and thus prevents crazing.
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es: ESMALTE DE PLOMO
Lead glaze in traditional pottery was used to glaze large pieces, in both usable and decorative ceramics, applied in the form of galena or litharge. Today its use is forbidden and lead compounds are sold as commercial frits which are subjected to health checks.Lead oxide is the strongest flux in pottery, it gives an attractive shine to colors and when in reduction a metallic shine. In combination with silica and kaolin due to its toxicity when crude, its use is limited. It is not advisable to apply it as powder and it must be fired in very oxide atmospheres and never for usable objects.
In porcelain, the body and the glaze fuse together in one firing between 1200º C-1300º C. It is strong and of a very fine quality and lends itself to the formation of thinner work. Beautiful effects can be achieved before firing by incising and cutting the raw clay. It can be decorated using colors and fired again.
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es: ESMALTE ETAPAS
1. Glaze as powder.
2. Glaze as liquid: the powder is mixed with water and the liquid, when fired, forms a transparent glaze.
3. Glaze-base opaque: glaze mixed with water and products to make it white and opaque
4. Glaze colors:
a) Glaze mixed water and color; a transparent colored glaze.
b) Glaze mixed with water and colors; form opaque colors to use with many different ceramic methods.
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Glazes types can be divided into several groups and are defined by their appearance, which can be; transparent, glossy, matte or satin. They are also determined by the firing: low, medium or high temperature which is required for the making of pottery: red clay (980-1100° C) earthenware (1100-1200º C) ceramic, refractory and porcelain (1200-1300° C.) The function of the firing of the glaze is to waterproof and maintain the shape after doing so at the required temperature.
A transparent glaze, when applied, is like a putting a layer of glass on your work, you can add small amounts of oxides so it continues being transparent, allowing you to see the decoration or the clay underneath. They are usually bright enamels.
Opaque glaze, is when an opaque substance is added to the base, such as tin, zirconium, titanium, etc., which makes the base white and opaque; it can be shiny, matte or satin.
Other methods are based on a recipe that gives specific characteristics and aspects; crystallizations, celadon, tenmokus, chandeliers, raku, crackle, ash, salt, etc.
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es: ESMALTE, GRES
Stoneware glazes are fired between 1200º C-1300º C and are usually slightly shiny and can produce some superb colors. If fired twice, some colors become completely matte and can change their color. If there are two or more colors in a design, care should be taken to keep them separate, as they will run into each other if they are touching while being fired.
WARNING: Many glazes and stains can be toxic or give off poisonous fumes. When you buy your materials, be sure to know what they contain and the appropriate precautions to take when using them. Wear a mask and gloves when working with chemicals and make sure the room you are in is well ventilated. Great care is needed when there is the danger of inhaling fumes or using a spray that contaminates the air.
IN-GLAZE; is when the glaze-base and decoration are fired together. A piece of ceramic in the bisque state is covered with an opaque glaze-base and then decorated with colors; they are both fired together at 980º C and fuse and integrate to form a shiny glaze that accentuates the colors and leaves a smooth, vitrified, unbroken surface, so you cannot feel or see different levels. Read more about: In-glaze
ON-GLAZE; is firing a piece of pottery three times. The first firing turns the clay into bisque, for the second one you cover the bisque with an opaque glaze-base and for the last one it is decorated with colors. (This is also known as enamel decorating.)
Read more about: On-Glaze
UNDERGLAZE; are ceramic colors applied on to bisque or clay and covered with transparent glaze. The colors and the glaze can be fire separately in two firings or together in one.
Read more about: Underglaze
SLIP GLAZES; are transparent or opaque glazes that can be prepared with colors and textures. They are put onto the clay when it is dry, then both are fired together.
Read more about: Slip /Slip Casting / Slip decorating
Tin oxide is the main ingredient of glazes-bases and is used for its whiteness and opacity. There are many different types of glaze-base, made up with different formulas and textures, matte, semi-matte and crackle, etc that can be applied onto ware in different ways and that vitrify at different temperatures and all can be purchased ready-made. When bought, it is in powder form, then mixed with water and laid over tiles, plates and jars that have been bisque fired. Application in both methods can be made by spraying, painting, burnishing, dipping, pouring, etc., depending on your desired results and the thickness of the glaze is determined by the amount of water added and needed. A glaze that has an off-white tone helps to achieve an antique look.
The methods used will depend on the type of clay the bisque is made of and to what temperature it can be fired. In the case of red clay, glazes can be used that mature up to 1100º C, and if refractory, they can reach 1300º C. Ones that vitrify at different temperatures can be added to the same design, always firing at the same or lower temperature than the lowest used, never higher.
Glaze-base types: There is a large selection of glaze-bases that can be purchased already prepared. The following are four common ones:
Glaze Crackle: glaze-base prepared to leave a crazed surface after being fired.
Glaze White: a strong white, has a very industrial appearance and a strong glaze finish-
Glaze Semi-Matte: white with a soft glaze finish.
Glaze Matte: without any shine. *Glaze “Siglo 18” (Spanish for 18th Century)*It is the one I prefer as it has an off white color which helps to give an antique look.
a) The glaze-base we use when working with the Majolica method in Spain leaves a surface that has an off white color which helps to give an antique look. It is called “Siglo 18” (Spanish for 18th Century)
b) Glazes or glaze colors, which have foreign bodies to form textures, cannot be sieved, as this would separate them from the glaze, crackle is a good example.
Note: Before starting to apply the base the bisque must be cleaned and sounded, this is explained in the follow four sections. Read more about: Bisque (a) Cleaning tiles to use / Bisque (b) Sounding tiles / Bisque (c) Sounding plates, jars and lids /Bisque (d) Cleaning plates, jar and lids
Half fill an ordinary bucket with water, add the glaze-base in powder form and mix them. The best method is to buy a long metal whisk that can be used with an electric drill but it can be done by hand, wearing plastic gloves to press out all the lumps and stirring. Continue adding glaze-base and water until you have a bucketful with a thick, creamy texture, thoroughly mixed.
The prepared glaze-bases are kept in a containers, designed as part of a table, which are used for working in and storing. Read more about: Table – Glaze-Bases
a) Across the container, from side to side, lay two long, strong, flat bars of wood. They should be far enough apart to balance the sieve. The sieve can be an ordinary wooden one, metal or rotary.
b) Pour the mixture into the sieve and press it through into the storage container. Discard any solid bits that cannot be broken up and are left in the sieve. When finished, clean and wash the sieve well.
Remember to scrape up and keep all the glaze-base that is dirty, dry or wet that falls off during the process of preparing and put it into the box where you keep the dirty glaze-base as it can be cleaned and used again. Read more about: Glaze-Base (f) Cleaning it of tiles
Note: Sieves: You need three; a rotary sieve for large quantities of glaze-bases, which comes with changeable plaques with different sizes of mesh, for a glaze-base use a mesh of 80; a normal sieve for quick jobs; and a small one for colors. These last two do not have changeable mesh. The small one for colors is made in two pieces, a funnel and a sieve, and this makes passing the liquid into narrow bottles or jars very easy.
Read more about: Sieves
By controlling the viscosity and specific gravity of the glaze-base, the desired glaze thickness can be achieved. The porosity of the bisque will determine the absorption rate, and is dependent on the type of clays it has been made with and temperature to which it has been fired. As you work with different types of bisque and firing schedules, you will obtain a feel for the porosity and how thick the glaze should be.
I have found that handmade, brown clay bisque needs a thick coat of glaze-base; white bisque needs more water and industrially made, brown clay tiles even more. If the glaze is too thin, when fired, the color of the bisque can be seen through it but you might want this, as it can help to give an antique look. If the glaze-base is too thick, it can cause problems such as lifting, crawling, etc., during the firing. You must experiment to determine your taste and the right consistency to match the type of bisque you are using. To test the thickness of the glaze-base, prepare one tile with it and wait a few seconds until it has dried enough to move it. It can then be checked in the following ways:
a) If the glaze-base on the back of the tile, is around the edges and lumpy, it is too thick. Simply add more water and stir.
b) If the glaze-base is too thin, leave it to settle; the glaze will fall to the bottom and the water will form a layer on top. Scoop out the unnecessary water, using a slightly curved plate. Stir well and start again.
c) When you are stirring the glaze-base by hand, pull out your hand, close your fist and the glaze on the back of it gives you a good, quick idea of its thickness.
d) Scratch the glaze-base on the tile with a fine instrument to see its thickness. I use a straightened paper clip for this.
Testing equipment such as hydrometers, viscosity cups, and viscometers can help in testing the density of your glaze.
Keep the water you remove; even though it looks clean there is still a lot of glaze in it. Let it stand and the glaze and water will separate. If the glaze is clean, stir it and put it back with the prepared glaze. If not, pour off all the excess water and scrape the damp glaze into the box in which you keep this type of dirty glaze.
Read more about: Boxes for dirty glazes
Note: See:Bisque (a) preparing to use. It has three sections (a), (b) & (c). It explains how to clean tiles, plates and pots, before putting on the glaze-base.Preparing to work. The bisque tiles you are going to use must be cleaned and sounded. Lay out two or three tiles. The number of tiles will depend on the size of your container. Pour the glaze over them, starting with the tile on the left and finishing with the tile on the right. There should be enough space between each of the tiles for the glaze to fall through and they must be vertically straight, or else the glaze will run and leave an uneven surface.
a) Using your hand, mix the glaze-base until it has a uniform consistency throughout, making sure there are no lumps on the floor, walls or floating on the surface and that the thickness is right for your work.
b) Place the stack of tiles that have been prepared to use to the right of the basin, on top of a wooden board. The board helps to keep them clean, it should be narrower than the tiles, to make picking them up easier and also long, so that it can be picked up and used as a tray.
c) To support the tiles, lay the wooden frame across the top of the basin.
d) Lay the tiles, right side up, on top of the frame.
e) Dip a small bowl into the basin, through the space between you and the tiles and fill it with the glaze-base
f) Hold the bowl in your right hand, with your thumb inside the bowl and your fingers on the outside.
g) Lift the bowl, holding it to your left side and with the liquid facing outward, over the back, left corner of the tile. Now, move your hand smoothly, tilting the bowl so that the glaze-base runs out and over the tile. If done correctly, a smooth layer of glaze should completely cover the tile.
h) Repeat this for each tile.
i) When finished, lift the tiles and put them on the boards to your left. Be very careful. If you move the tiles before the damp shine of the glaze has disappeared, the glaze-base can run, leaving an uneven surface.
Important: To keep the glaze-base homogeneous, you must keep stirring it so that the glaze ingredients remain in suspension. If the glaze is not thoroughly mixed, it could result in glaze defects on the surface in the form of patches, which can be seen after the ware is fired. When you have finished, remember to stir the glaze-base before leaving it. Read more about: Bar – Tile supports / Container – Glaze-base
When the glaze-base is dry enough to clean, you can stack the tiles in pairs, face-to-face and then back-to-back. If they are not dry enough, they will stick together and be unusable when separated. Place about ten pairs in a stack and then begin to clean the edges and backs of the tiles. The less you touch the glaze-base, the better. Your hands are naturally oily, and oil is incompatible with the glaze. As you work, move the tiles from one side of the table to the other. Start the cleaning process with the tiles stacked on your right. When the sides have been cleaned, move the tiles to your left and when the backs have been cleaned, on your right, then when dusted and finished back to your left.
Remember: All the glaze-base taken off can be cleaned and used again
To clean off the glaze-base you must have several scrubbing brushes with natural bristles and wooden frames. The more you use them, the more the bristles wear out, the stronger they become and the better they work, so keep them at varying stages of wear. The worn out ones are good to clean the back of tiles, on which there is a lot of thick glaze. This is a difficult part to clean because the tiles are manufactured with protruding designs or trademarks which collect and hold the glaze-base. To finish the cleaning, use a brush with long hair, to take off the last of the white dust.
a) Cover a table with a large piece of plastic Have several wide bars of wood on each side to put the tiles on during the stages of cleaning.
b) Put pairs of tiles, with glazed sides facing each other, in stacks of about ten on your right, on top of the wooden bars.
c) Clean the tile edges, then move them to the left.
d) Have a small rigid container, about 13cm high to put the tiles on when brushing the backs. Clean the backs move to the right.
e) Dust and repair, move to the left.
Cleaning the sides.
When one side is done, turn the pile and clean the next side, until all four sides have been cleaned. The three ways outlined below to clean the tile edges are in my order of preference.
Note: With the first two methods, when you lift and turn the tiles around, to clean the sides, clean off the glaze that has fallen onto the board you are working on, so it cannot dirty the parts that are already clean. Loose glaze can be forced up between the tiles and damage the glaze-base.
Cleaning with your fingers.
Hold several pairs of tiles sideways on top of a bar of wood and run your index finger along the edges, lengthwise, to push off the glaze, turn and clean all four sides. In the past, old leather gloves were used for this. The last three fingers and thumb were cut off the glove; then, the first finger and the rest of the glove were used as protection. To do this use a plastic glove but if you find it awkward to work with, just cut off one glove finger and use it to cover your first finger.
Cleaning with a scraper.
Holding several pairs of tiles, edges up, on top of a bar, use a plastic scraper to scrape the glaze-base from the edges, moving it lengthwise.
Cleaning with a brush.
Strong brushes are needed and before starting to clean the edges, make sure the sides of the tiles are even. To check this, hold several pairs of tiles together tightly and stand them on their sides or pile them on top of the rigid container, where they are going to be cleaned. Then hold the flat back of your brush against one side and with your hand on the other side, flatten them out. Hold them down with one hand and, with the other hand, use the end of the back of the brush, to scrape off the glaze, moving lengthwise along the sides of the tiles.
Then, brush the sides using a downward movement until they are clean.
Remember, when brushing the sides; always brush down the edges, not lengthwise, because the bristles ban go between the tiles, scratch and damage the glaze
Cleaning the backs.
Once all the sides are cleaned, clean the backs. Pick up the pairs of tiles and put them on top of the container. With your most worn-out brush, which is the strongest, clean the backs of tiles, brushing the glaze off and outwards, the cleaner the better. Turn the tiles so the edge of each side is brushed outwards. Make sure that the edge of the underneath tile does not protrude, as the bristles could overlap and damage its glaze-base. If they are not clean enough, brush them again with a longer-haired brush, then pile them up on top of a clean bar of wood.
Finishing the cleaning.
Pick up the tiles, one by one, holding them by the edges. Slant the tiles downward and tap on the top edge to knock off any loose glaze. If there is still some left, clean it off with a large, soft, dry brush. Gently rub any small holes with your finger. If a tile is badly damaged, put it aside so you can later repair all the damaged ones together. Lay the finished ones out on the shelves to dry.
Warning: Industrial tiles used to be very good to use but the manufacturing methods have changed and with this many new problems have appeared, most of them during the process of the glaze-base drying. They are now made lighter, thinner and stronger and something in them reacts against the glaze-base. Before, when the base was put on and cleaned, you could stack them one on top of the other, face-to-face and leave them for months. Now you can not do this as the glaze-base forms a rash, which is like hundreds of very hard, fine bits of sand and makes them unusable. Now you must lay them out, individually, on their backs to dry. There is a photo in the dictionary showing our corridor, with many movable shelves, full of tiles left to dry. When dry, after two or three days they can be piled up face to face.
Note: The cause of this problem is that modern bisque is so strong, when the tiles are stacked, that the glaze retains its dampness as it cannot escape. For certain clients we buy handmade or semi handmade tiles and these do not react in this way, but they are thicker and this makes everything more expensive, so we only use them when they are especially requested and the client is willing to accept the price. Here I have not explained these problems and their remedies as I am assuming and hope the readers can still buy good quality tiles.
Read more about: Tile – Problems
Preparing the glaze-base.
a) Prepare the glaze-base in the same way as for tiles.
b) Make sure you have enough glaze-base. It has to be deep enough to completely cover what you are preparing and the density and viscosity must be correct for your work.
c) If you are using the same glaze-base that you use for your tiles, you might need to change its density. When the products are handmade, both brown and white bisque, the base needs less water, and it must be thicker for brown than for white bisque. To thicken it, before mixing, remove the excess water. Using a very slightly curved plate, skim off the water and keep it.
d) Remember, keep the water, as it can always be re-added and when you finish it can be put back, it has glaze-base in it so do not waste it.
e) Before starting to use the glaze-base, stir and mix it well.
f) Have wooden boards next to the container to stand them on after being dipped.
Applying the glaze-base, by dipping.
PLATE: Using your index fingers, hold the plate on opposite sides and dip it into the glaze-base at an angle of 45º. Your right hand goes into it but only the index finger of your left hand. When the plate is completely covered, move it from left to right two or three times. Take the plate out, still using one finger of each hand, and hold it at an angle of 75º over the glaze. The base dries in seconds and any excess glaze drips off
JAR: Hold it at the footing with your left index finger and the neck edge of the jar with the right index finger. Slowly put the jar into the glaze-base, lower the part of the neck first, so the glaze-base flows inside it. When covered, turn it backwards and forwards so as to move the base inside the pot, so it goes round and covers it all. Be careful when doing this, there is often an air-block, which stops the base entering and covering the inside. When you remove the jar from the glaze-base, tilt it so the excess glaze-base runs out.
LID: Put your finger inside the lid and against the flange with enough pressure to hold it upside down. Dip it into the glaze-base, completely covering and moving it gently so the glaze gets right into the inner edges of the lid. Still holding it with your fingers, take the lid out and turn your hand, so it is the right way up, let the excess glaze-base drip off and hold it until it has lost its shine. Then take it by the knob, move it onto a bar of wood and leave to dry.
Note. With everything you have prepared, dip a brush or your finger into the glaze-base and hold it over the spaces that your fingers have left on the edges to fill them up with base. Apply more than is necessary as it shrinks and this can be corrected when being cleaned! Leave the work to dry and after about ten minutes you can start cleaning it.
Cleaning and repairing the glaze on plates, jars and lids
a) Plates; put a piece of wood on top of a hand wheel and a towel on top of the wood, and then place the plate upside down on top of the towel. This keeps the plate from slipping and prevents damage to the glaze while it is upside down. I always leave the plate slightly overlapping the wood. This makes picking it up easier. The following illustration shows this.
b) Clean the corners on both sides of the flange that connect it to the body, it can collect excessive base which can cause crawling or beading. If it is too thick, scrape down the glaze at these joints. Turn the wheel, using the banding bar to support your hand, hold a tool so it scrapes off the surplace glaze from these parts.
c) If the plate has hanging holes, clean the glaze out by passing a thin metal wire through them.
d) To clean the footing, use a cut down toothbrush and brush it in an outward direction. It is very important that the footings on plates, jars and lids are clean so they do not adhere to what they are standing on when being fired.
e) When being held at an angle to dry, the base may run off leaving a thick line, so scrape this and any other lumps down and remove any strange objects like hair, dirt, etc.
f) Dip a paintbrush into the small bowl of glaze-base for repairing and fill up any small indents and the holes on the edge where your fingers held it; in seconds these parts will dry and can be leveled out.
g) With a large, soft, dry brush, brush off the dirt or loose base then smooth these parts down, using a brush with water or a thin layer of base.
h) Finish by painting your name or trademark on the back.
i) Turn the work the right side up and repair any damage you see on the front.
j) Use a soft lead pencil and mark the center top, on the front of the plate. This mark should fall between the two holes on the back used for hanging the plate; this lets you know which way up the design has to be marked on.
k) Jars and lids are cleaned in the same way as plates and the trademark is written on the bottom of the jar.
The following instructions apply to glaze-base that is prepared and that you are going to leave to sit. First, stir the glaze-base well so there is no thick layer on the sides or bottom of the container. Then, with one hand, stir the glaze around and around, always going in the same direction, gradually letting the circular movement you are making become smaller and smaller. It is important to do this as just doing it for one minute, will prevent the glaze-base from hardening. It can remain liquid for months without being touched. When not in use, cover the basin to keep the glaze-base as clean as possible.
Note: Tables: The table that holds the containers, with the different glaze-bases, must be very strong as large quantities are heavy, so design it so that the lids form a table top that can be used.
Read more about: Table – Glaze-Bases
The drying procedure of the glaze-base and the drying time of a glaze-base depend on the temperature and humidity of where you are working, the type of glaze-base, its thickness and how absorbent the bisque is. There are four drying stages:
a. Dry enough to move.
b. Dry enough to clean:
c. Dry enough to decorate.
d. Too dry to decorate.
a. Dry enough to move: A few seconds after applying the glaze-base to the tile, you will see, looking at it from the side, that it has a brilliant, damp texture which, in seconds, shrinks as it dries. When this texture disappears, the piece is dry enough to be moved. You can lift it, touching only the back or sides, which will have to be cleaned and move it to a shelf to continue drying. If you do not want to waste time waiting for it to dry, put three or four bars of wood on the left side of your basin. As soon as you have poured the glaze-base over the tiles, while still shiny and drying, move them onto these wooden bars. While you have been working the glaze-base has collected round the wooden frame the tiles are balanced on. which can cause them to stick slightly, so when lifting them, hold them at two opposite corners and slightly turn each tile so it separates without tilting it. Having the bars on the table at the side of the container allows you to keep the tiles at the same level and not tilt them, so the glaze-base does not run and become uneven when being moved. Continue preparing tiles until the bars are full. By then, the first ones prepared will be dry enough to move onto the shelves. When moving them always use the top shelf first as, when you slip them onto the shelves, the glaze on their backs can be scratched off and fall, damaging anything that is underneath.
b. Dry enough to clean: After an hour, the tiles should be dry enough to be stacked for cleaning, face to face, glaze to glaze, without being damaged. Put them into groups of six to ten pairs. The drying time depends on the temperature and humidity of where you work and the type of bisque the tiles are made of and can take up to twelve hours. The more industrially made the worse they are and the longer they take to dry.
c. Dry enough to decorate: The glaze-base must be dry before you can begin decorating. This could take up to twenty-four hours. It has to be dry enough so as not to be pulled off by the dampness of your paintbrush. Dampness can also cause the colors to spread. You cannot see this happening, but, when fired, it can make the sharp outlines of your work look thicker and blurred, and the colors appear softer. If you want the tiles to dry more quickly after you have cleaned off the glaze-base, put them into a tile-stand, or lay them out where they are going to be decorated. Keeping the tiles together in piles helps to retain the humidity. In an emergency, put them in the kiln on low heat for a short while. Remember, it is easier to clean them when they are damp, but they should be dry for painting.
d. Too dry to decorate: When left for a long time, the glaze-base on your tiles can be so dry that, when painting, it will transfer to the brush like dust. To correct this problem, wet the glaze-base by lightly sprinkling it with clean water. Leave it for a while so the water spreads out evenly.
Alternatively, hold the tile horizontally, with the glaze-base facing down, and lower it into a basin of clean water. The tile should just touch the water, for a second, so that the front is damp and the back is still dry.
To repair glaze-base, keep some of the each one you use in pot with a lid, as this helps to keep it clean and in a liquid state. Have them in pots of different sizes, shapes or colors, or mark them so they can be quickly recognized, different colored electric insulating tape is good for this. Mix them well before using and if they start getting dirty, change them as dirty glaze-base will be seen to be a shade darker after firing.
While cleaning the glaze-base off tiles, you might find that some are damaged. The damage can be in the form of lumps, dirt, holes left by air bubbles, or scratches. To repair lumps, use a very fine piece of metal to scrape them down. If the damage is some strange fiber, it will burn away when fired and leave a space, so remove it and repair the place.
To repair the damaged parts, dip a paintbrush into the glaze-base that you have kept separate for repairing and fill them up. This makes lumps, so let it dry for a few minutes, then scrape it down to the correct height and brush off any loose glaze. Finally, using a soft brush, with thin glaze-base, smooth the part down.
Cleaning: When you have finished, keep the glaze-base that has been brushed off. Scrape it off the walls, tables, wooden bars, and tiles you do not want to use. If you have tiles that have started to be decorated but have been damaged, scrape off the glaze with the colors and throw it away. Then scrape off the remaining clean glaze-base, using a plastic scraper or a strong dry brush. Put what you have recovered into the correct box for this type of dirty glaze.
Note: We have three different types of glaze-bases permanently prepared which are kept in large plastic containers. Each container is a different color and they form part of the table where I prepare the tiles. I have three plastic boxes in the same colors as the containers, where I keep the dirty glaze-base of each type. When a box is full, add water and pass it through a sieve back into the container with the same type of glaze and mix them together.
It is impossible to keep the prepared glaze-base from getting dirty. When you have a small amount left in your container, clean it before preparing more. Pour the remaining glaze-base into buckets; clean and wash the container; pass all the dirty glaze-base through a sieve and back into the container and then prepare more.
Read more about: Glaze-base preparing / Glaze base thickness
Glaze–base textures: This refers to textures made by applying the glaze-base to the bisque using different techniques.
Dripping: You can use anything from a bag for icing cakes, an injection syringe or a large soft brush. You literally drip the base or paint onto the object you are decorating. Different colors should not touch each other, unless it is part of the planned design that they should mix. Dripping can be done on to dry clay with slip, with colors over a glaze-base or colors directly on to bisque to fill spaces and leave textures.
Sandwiching: Prepare two tiles with a color or glaze-base and straight away, while they are still damp, join them face-to-face. When separated they will have a rough texture. The quicker this is done and the damper it is, the rougher the texture will be. Leave to dry and then clean backs and edges.
Spattering: to make an uneven texture by using glaze-base that has become sedimentary and the water has separated from it. Before stirring it, take a small basin full of thick base and put it to one side. Then stir what is in the container, adding water to make a very thin substance. Prepare your tiles with this glaze-base and leave to dry. Next, either holding the tiles in your hand or laying them on the woods over the basin, dip a “brush of palm leaves,” or something similar, into the bowl with the thick glaze-base and shake it over the prepared tiles.
This will create a heavy spotted texture, leave to dry and then clean the back and edges. Be very careful when piling them up face to face, and try not to put too many in each pile. This technique is good for designs with a lot of white in the background, as the texture breaks it up. If painted, the different thicknesses give shadows to the applied glaze-base. This can also be done with a colored glaze.
In the same way that you can add grog to clay; you can also add other substances to glaze-bases or glaze-colors to give different textures. Some of these will burn away, such as rice and wood; others like bisque and sand will not burn away and will leave a rough antique texture. Make sure the solid ones vitrify at the same or higher temperature than the glaze; otherwise they may melt and bleed. Bisque can also be useful for creating textures. Break down the amount needed in a mortar or sandpaper the bisque and use the powder that has been filed off. If you have an electric machine for cutting tiles, keep the powder that gets thrown off. Pass it all though a sieve before mixing with a glaze-base or color.
Read more about: Grog
The next five designs have had the glaze-base shaken on to them, as previously explained. The photos are to show different effects made by applying colors, in different ways, on to textures.
The method of working:
1) The plates are dipped into a thin glaze-base and it is poured over the tiles.
2) The tiles and plates are then spattered with a thick glaze base using a palm-brush or something similar, to form the texture you want.
3) For “a” & “b” the tiles are laid on to a board and the board is put on to a wheel so it can be turned. The shape of the design is cut out of paper and laid on top of the tiles and weighed down, it is then sprayed with the color. Hold the spray at the side, at the height of the tiles. Spray the top part lightly so as to give the idea of sky and let it thicken as it gets to the bottom, to give the idea of ground. Do not spray it straight on top as it would even out the color, losing the contrast of textures and uneven colors that are accentuated by the surface. This can be seen very clearly in the first two photos. Take the paper off, mark on the outerlines of the design and paint them. Clean off any of the color left and level off any parts inside the outlines if needed, then mark on the whole design and paint it.
4) Plate; mark on the design and paint it. Then with a large soft brush, using green copper, paint the background.
5) The rooster is done the same way as in 4 but for the yellow background use a thick color with a very soft brush so as not to flatten the texture.
6) This plate is done in the same way as in 4 & 5 but the background is not painted so when fired the color of the red bisque accentuates the different textures of the base.
a) Cleaning up used glaze-base: Keep all the dirty glaze-base that has been cleaned off work, backs of tiles, feet of plates and jars, etc., it can all be used again. Keep the different types of dirty glaze-bases separate, each in their own colored box. When you have a large quantity, add water, pass through the sieve and back into the container which holds the same glaze.
b) Cleaning the liquid glaze-base: However hard you try to keep the liquid glaze-base clean in the container, it will collect dirt and have to be cleaned. When the amount is low, take it out and put it into buckets. Wash and clean out the container, then pass the dirty glaze-base back, through a sieve and prepare and add more.
Cotton gloves: Plastic gloves are clumsy to use. Use cotton gloves for work when you do not have to put your hand into a liquid. They do not keep your hands dry but prevent the colors, powders, etc., from damaging your skin. Cotton gloves can be tight fitting and washable.
Plastic gloves: Working in ceramics may damage your skin, so it is advisable to wear plastic gloves as much as possible. There are specially made ones for potters, but also ordinary household ones are practical. Unfortunately these haven’t got the extra-long part that covers the arm, so that when you mix a large quantity of liquid, like a glaze-base, it may enter inside the glove. Buy different sizes always in the same color so you do not waste time trying them on.
Plastic finger: Using a broken plastic glove, cut off one finger and use it, on the first finger of your right hand, to clean off the glaze-base from the edges of tiles. Hold three or four pairs of tiles together, stand them up on one side, pull your finger along the edges, taking off all the glaze, turn and clean all the sides in the same way
Kiln gloves: A special type of glove made to resist the heat and are usually made of leather. They can withstand heat for short periods and are used for removing work from a kiln.
Glue is an adhesive in liquid or semi-liquid state that adheres and bonds items together. Glues come from natural or synthetic sources and are used for bonding the same or different types of materials together. Most adhesives need time to dry and adhere. There are now new ones that react straight away but are sold in very small quantities. The next five sections cover glues used in ceramics.
ca: GOMA - Aràbiga
es: GOMA - Arábiga
Arabic glue is a natural product and will burn away when fired, it is a gummy substance taken from a certain tree and is used in pharmaceutical work, mixed with food, inks and colors for printing. In ceramics it is used as a retainer, to hold colors on to a glazed surface that they cannot normally adhere to, as with the on-glaze method.
Rub the part that has to be repaired or painted with a thin layer of glue and leave it to dry. As the surface is glazed, nonabsorbent, this will stop the colors from running. When you have finished painting, carefully cover the part with a thin layer of glaze and then fire it again. This gives a varnished surface, like the rest of the tile, to the part you have repaired.
Do not prepare this glue until needed, it dries very quickly and then it has to be thrown away.
3 Gr. kaolin.
1 Gr. Clay
1 Gr. calcined alumina
3 ml. sodium silicate
Mix them all together, so as to form a thick paste. Lay it on both sides of the pieces to be joined and hold them together until they are firmly stuck. If it is a space fill it up with this glue. Fire the pieces, then decorate and fire them again. These have all been fired at 1280º C. Remember that until they are fired the glue has not vitrified and the pieces still can separate.
a) The first photo shows the bowl cracked.
b) The crack has been filled up with the glue and fired. As it is a different product to the clay it has a different color.
c) The piece decorated and fired at1280º C.
All glazes can be used as glue. Put the glaze-base on the two parts of bisque you want to stick together, hold them until it dries and then fire them. Remember the pieces must be fired to the temperature the glaze is made for.
ca: GOMA - Casolana
es: GOMA - Casera
If you have a piece of work in relief which is broken, or with a small part missing and you want to repair it without having to re-fire, a very good and strong way to do this is to mix carpenters’ glue with cement. It can be used to fill up spaces or join pieces. Lay it on to the parts that have to joined, hold them together until they dry, then file down any rough edges. These parts can then be painted with industrial emulsion colors.
ca: GOMA - De fuster
Carpenters’ glue is very good for mounting tiles on to wood for framing. It is reliable, does not wear out with time and if you want to remove it from the wood, just soak it in water for about 24 hours.
Read more about: Framing and mounting tiles
Goggles should be designed so that they are sealed tightly to your face to exclude airborne dust and liquid from touching your eyes. They can be purchased with anti-mist lenses and dark lenses for viewing the bright light of a hot, open kiln. Buy cheap goggles also to wear when cutting tiles and be very careful when cutting glazed tiles as sharp bits fly off and this is dangerous. There are many types and they are also classified in catalogs under shields, masks.
Read more about: Mask – Respirator
es: VERDEClick on the title to see more images
Green is a very important color in the Majolica method and green copper oxide is one of the main ones used. You can mix and make up colors to your own taste. The following, going from right to left, are the four I use in the Majolica method.
1) Green copper: 1-green copper oxide (Cu2O)
2) Green light: 1-yellow (Si-Zr-Pr) + 0,250 green strong (Co-Cr)
3) Green strong: 1-green strong (Co-Cr)
4) Green dirty: 1-green (Co-Cr) + 0, 50 yellow (Zr-Si-Pr) + 0, 05 orange (Pb-Sb-Fe)
GREENS – PAINTING WITH THEM
5a) Grape leaves: The leaves have a large space of yellow round the edge and the center is green copper, which overlaps the yellow and as they both have different intensities this gives a large variation in colors.
5b) Grapes: Yellow is put in the center of each grape leaving a small space of the white base on the left and a larger one on the right. Then this space and most of the yellow is covered with light green and shaded slightly with strong green.
6) Jacket: Strong brown, lightly painted under strong green.
7) Trousers: Dirty green shaded lightly with strong brown.
8) Bushes: Yellow overlapped with light green and shaded with strong green.
ca: VERD DE COURE
es: VERDE COBREClick on the title to see more images
Green Copper: The plates below are copied from a photo; the original is in the Ceramic Museum of Barcelona. It was originally painted after 1400 AD in Paterna, a town in Valencia. When this style started it was known as Bicolor as it uses two colors only, manganese and copper green. There is also Tricolor which uses three colors; the most common colors for this method are green and blue.
Copper oxide is a green color used over and under other colors to create different colors and shades. If used heavily it becomes black with a silver shine when fired.
The photos below show green copper in different ways and with different colors.
a) b) c) d) Copies of antique plates: which only use two colors manganese and green copper.
e) Collecting grapes; shows the whole picture.
f) Close-up of the leaves; two thirds of each leaf is painted with yellow, green copper covers the last third and also half the yellow.
g) Jacket; yellow with green copper on top.
h) Jacket; shaded lightly with dark brown then covered with green copper.
i) Jacket; shaded with blue then covered with green copper.
es: MOLINOClick on the title to see more images
Grinder is a machine that has functioned through history by hand, horse, water, wind and electricity. It is used to break down hard products into particles. In the past they were made in two parts, the floor that was flat and static to hold the product and the grinding stone, the upper piece that was turned so it rolled and crushed what was between them.
Above from left to right:
Grinding olives: Grinding grapes: Chemist mortar: Grinding corn.
Ball mill is an electrically controlled machine that turns, grinds and mixes materials.
Read more about: Ball mill
Grog: is a granular material that has been crushed down from brick, refractory rock, or other pre-fired ceramic product and added to clay to give textures, reduce shrinking during firing, help the clay to form uniformly and stop cracking and warping when being fired. Grog can be made of many varied substances, of different thicknesses and colors. Make sure the grog can be fired to the same or higher temperature than the clay it is going to be added to. It can be obtained from cutting or filing tiles. When using an electric tile cutter it throws off bisque in powder form, which is grog.