This page is for those seeking more information about Slip Cast ceramics etc.
Frequently Asked Questions
WHAT IS "SLIP CAST CERAMICS "?
Slip refers to clay in a liquid form. Slip casting involves the use of moulds (which are made of plaster) to form a shape.
This is done by pouring the slip into the mould and allowing it to “set up” to the desired thickness. The excess slip is then drained out leaving a layer of clay against the wall of the mould.
After a short drying time, the mould is opened, the clay shape taken out and trimmed of excess clay. At this point the clay is still very soft and is referred to as” leather hard”. The piece is them put aside to dry.
When dry it is referred to as “Greenware”. A lot of decorative work and painting is done at this stage.
To become mature the clay requires firing. Once it is fired it is referred to as “bisque” meaning “fired clay”.
Earthenware bisque is porous and needs to be coated with a glaze, refired to make it impervious.
Slip casting opens up a world of its own. The piece can be decorated using many techniques in such a way to make it a ‘one off’ and completely individual work.
The best way to learn is in classes. The VHCA can suggest studios in your area. Being a member of the VHCA, keeps you up to date with the latest in ceramics and exposes you to a huge variety of skilled people.
HOW DO I ENTER THE VHCA ANNUAL SHOW?
Take a look at the Forms and Downloads page on this website for your entry form and guide . If in doubt just email us via the contact page and we can help you!
Also provided below is a collection of helpful hints on everything to do with ceramics and your kiln, firing, glazes, lustres, all sorts of things.
Listed below are hundreds of hints listed for you in random order.
If you wish to search for a certain keyword or subject press:-
Ctrl (with one finger) and F ( with another finger) on your keyboard. Then press Enter.
Either in the middle of your screen or in the left hand corner, a box will appear. Enter your keyword or phrase and press ENTER.
Your selected word or phrase will appear in the relevant text. If you press "NEXT" you can continue to search through this whole document here for the same reference.
EG.
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Happy reading and if you find something is not quite right with this information please email and let the VHCA know. We would love to hear from you.
Firing reds
The red family of glazes is easily contaminated and requires more venting and a faster firing schedule.
Loading the Electric kiln
It is important to remember that one element groove must be between every shelf with the exception of half shelves.
Glaze positioning
Leave at least ½” between all pieces when loading your kiln. Remember that the piece will expand during the firing cycle before it contracts and shrinks.
Substitute for hot waxing
<!--[if !supportLists]-->· A good substitute for hot waxing or wax resist is Mop-n-Glo (floor wax). Not only is it cheaper, but it will prolong the life of your elements in an electric kiln. The fumes are also not as toxic and you don´t get the smoke from burn off! (L.M.)<!--[endif]-->
Shivering
Shivering: Sometimes a piece of glaze will crack off, normally near a rim or at edges. Some clay may be attached to the glaze piece that cracks off. This occurs because stress has built up between the clay and glaze that can´t be absorbed. It is often caused by over-sponging which takes away the fine clay particles and leaves behind the groggier clay particles which are not elastic enough to absorb the stress.
Saving Kiln shelves
„h To prevent glaze from running onto your kiln shelves, cut some slices of kiln brick and fire your pots on that. The brick will stop the glaze from running onto the shelf. Excess glaze can be removed with an angle grinder (use caution with this tool!) Shelves will last much longer, if not indefinitely!
Applying kiln wash
Make sure you have a good layer of kiln wash on the shelf. This is to facilitate the removal of glaze drips. Do not apply kiln wash to the sides of the kiln, or underside of the kiln shelves. The wash is likely to flake off and land on your glazed pieces.
OH&S/Be prepared
Every object in the raku area should be treated as if were capable of causing severe burns instantly on contact with your skin. This includes bricks, kiln shelves, tongs, pots, peep-hole plugs, reduction containers (garbage cans), water buckets, and all parts of the kiln. Before you touch anything, confirm that it´s not hot. Anything that is hot (especially bricks or kiln shelves removed from a hot kiln) should be kept out of the way of passers-by and preferably cooled by a squirt from the hose or a dunk in a bucket of water.
Glaze and body fit
Glaze and body fit?
Since the glaze and the body on which it is fired (bisque) are made from different materials, it is important that they expand and shrink a like amount when heated and cooled. If they don´t, then the fired glaze can be stretched to the point where it can crack (crazing), or it can be pushed together on to itself to a point where shivering or crawling occurs.
Raku firing tips
Since there are so many firing variables that affect the appearance of raku, it´s a good idea to eliminate as many as possible when experimenting with raku. Try concentrating on learning how to fire one glaze at a time, and use one easily duplicated form. Identical pieces heat and cool at the same rate, so you´ll be much more likely to see how the other factors tie in if you eliminate the variation in the weight of the pieces. Once the basics are clear, it´s fairly simple to branch out to other forms.
Firing raku lustres
Lustres need a very heavy reduction while the glaze is still hot, so it´s best to move them as quickly as possible from the kiln to the smoking container. A small container holds less oxygen, so using the smallest container possible will help to obtain a heavy reduction. Because the piece comes in contact with the combustibles while the glaze is still soft, lustres usually show some scarring in the glaze surface.
Oxidized firing
In an oxidation firing, ceramic wares are heated to a certain temperature. The heated ceramics draw oxygen from the kiln chamber and from the flue burner ports, spy holes and any other holes or cracks in the kiln. The oxygen combines with carbonaceous materials in the glazes and ceramic body, turning these into ash. Metal pigments in glazes, such as iron, will oxidize, giving the glaze a particular color. Oxidation firings can be done in most kilns, except those which are not designed for it, e.g. a black firing kiln, where sugar is introduced into the kiln which volatilizes and creates carbon, which is trapped in the clay body, creating a black surface. To do an oxidation firing, leave the burner ports and any damper open, so enough air exchange can happen in the kiln. In electric kilns, oxidation is the norm.
Bisque firing
For a bisque fire in particular, you need to drive off the water that is left in the pot. If you fire too fast, the steam will cause the piece to explode. (This is true even if the piece is very dry, because there is still moisture inside the clay molecules.) So it is important to fire bisque slowly.
If your pieces are not completely dry, you may want to candle them first. Candling is done on a manual kiln by turning the bottom switch on low and holding it there for several hours (6-10). With an electronic kiln, you would program the kiln to remain at around 150 degrees F for this time.
Firing lustres
If you should happen to get broken, wiggly lines on your piece after a gold firing you may be over-firing.
Use sand to stop glaze running onto shelves
How to fire mid range stoneware
(cone 6). kiln wash flakes and sometimes mars a piece in glaze firing. Therefore, use a layer of sand (the same kind that is sold in plastic bags at KMart for kids´ sandboxes. Spread the layer very carefully on the shelf after it has been positioned, approximately 1/8 of an inch thick. If you suspect that the glaze will run then use a heavier layer. Since sand will not melt until cone 28 there is no problem. The benefits are that the sand will absorb any glaze which may run off the pot and therefore the piece can be removed from the shelf without damage to the shelf or the pot. Occasionally some sand adheres to the vessel this is easily hand ground with a stone or machine ground with my Makita grinder. It is important to remember to put the sand on the shelves after they are in the kiln and keep it ½ “ away from the edge of the shelf in order to avoid contamination. I have not had any problems with sand particles getting in my glazed pieces and I do have a venting system. The secondary benefit is that pieces with large flat bottoms never warp! I also use the same technique for bisque firing all platters.
firing jewelry
A bisque tile can serve the same purpose as a shelf when firing jewelry or other light pieces
Raku Body
When making pieces for raku firing, consider the stress the process puts on the work. The thermal shock will crack large pieces made from most fine textured clays, so it´s best to use a body containing sand or grog. Long Beach is good for medium sized pieces, and B-mix with sand will work if you need a white clay to use with crackle. Large pieces should be made of a coarse raku or sculpture body. Any piece that´s at risk of cracking or exploding in a stoneware firing is doubly at risk when raku fired, so be sure to construct raku pieces well. While the clay is still in the bag, consider how to design the piece so it can be sensibly removed from the kiln with tongs. Avoid extremely fragile pieces or very heavy thrown pieces.
To get like firings every time
To get like firings every time, you must place your cone in the automatic kiln sitter in exactly the same way each time you fire your kiln
Repairs
Many repairs on your kiln can be done by removing and old or damaged part and inserting a new one.
General Raku firing
Learning to fire raku well is an exercise in patience, control, timing, and, observation. The results depend not only on the course of the firing in the kiln, but especially on the timing of the smoking as the piece cools. Some of the important factors are the temperature of the pot as it comes out of the kiln, how long it takes to get the piece in to smoke, the weight of the piece, the size of the container and the combustible material used for smoking. There are many special effects glazes each of which can vary quite a bit depending on the firing. The three main types of raku glazes commonly used are crackle glazes, lusters, and copper matts.
Mark your pieces
The worst thing you can do is fire low fire clay or glazes at high fire. The clay and/or glaze will melt all over your kiln and can cause major damage! If you have both low fire and high fire materials in your studio, you might want to mark your pieces differently on the bottom so you don´t forget and get them mixed up!
How to
The usual method of creating a reducing atmosphere is to close off the flue or chimney. This can be done by laying a piece of kiln shelf or kiln brick across the top of the flue/chimney, or if it is a larger chimney, by pushing in the damper (a piece of tile which can be pushed into a slot in the chimney, which is at an accessible height, reducing the air flow). Reduction firings are generally not recommended for electric kilns, although it is possible to achieve reducing effects by introducing combustible materials (e.g. twigs) into the kiln chamber through the spy hole. But the carbon monoxide tends to attack the kiln elements (electrical coils), which then deteriorate quickly.
firing
In firing a lustre/overglaze, the glaze is softened to the point where the overglaze settles onto the softened surface and becomes a part of that surface.
Overfiring an overglaze will cause colours to sink too deeply into the glaze resulting in distortion, fade-out or burn-out.
Keeping a firing log
It is very useful to keep a firing log. Start your log entry by describing how the kiln is loaded (types and sizes of items, density of packing.) You will find that the more densely the kiln is loaded, the longer it will take the kiln to reach the appropriate temperature. You will learn how to adjust for this with your particular kiln. Typically you will add a longer soak at the top temperature when the kiln is more densely packed.
Protecting the base
You can protect the bottom of your kiln by placing a full shelf there and coating it with kiln wash.
Firing Temperatures
Firing Temperature.
The speed at which the temperature climbs during a firing is critical, especially during the first 600c of a biscuit firing, as it is during this period that most of the physical and chemical changes occur. Once 600c has been reached, the clay has changed to a permanent ceramic material. Continuation of the firing to a higher temperature increases both the strength and durability of the ware. Gloss firings do not usually require the initial slow firing rate needed for biscuit, but they offer an opportunity to vary the glaze through using a range of atmospheres and techniques, such as raku, oxidation and reduction.
Time
The amount of kiln furniture you use in loading a kiln will effect the firing time too.
Raku Process
Raku Pottery is earth derived...the firing process is unique and daring, and in the eyes of the Zen Masters, the process truly reflects the most fundamental rhythm of enlightened life.
Read this entire article Raku Process
over-firing porcelain
If you have a piece of porcelain that comes out of the kiln without translucent quality, you may be pouring the piece to thick or be under-firing.
Loading: Around the Grooves
Be sure that at least one element groove is between the top shelf and the top of the kiln.
The first layer in the kiln should be small, light pieces.
Firebrick behaviour
The insulating firebrick expands and contracts with each firing. The expansion and contraction is necessary for the long life of your kiln, but some hair line cracks will appear in the brick while the kiln is cold. Do not be concerned about them, as they close tightly when the bricks expand when heated.
Opening the kiln
Do not open a kiln in the middle of a firing for any reason. let it cool gradually and you will not ruin any ware.
About Raku
Raku originated in Japan in the 16th century, where raku vessels were and still are used in the traditional tea ceremony. It is a low-fire technique, where bisqued work is quickly heated to red hot temperature and then taken out of the kiln and reduced in wood shavings, newspaper or a similar combustible material. Raku ware is decorated with low-fire glazes, which usually contain a lot of frit. The clays used for this firing technique contain a high percentage of grog, so the work will be able to withstand the high temperature fluctuations. Raku, with its battle with the elements of fire and smoke is an exciting technique, one that is suited to communal firings.
Do not use stilts with porcelain
Stilts cannot be used to support porcelain bisque as they become embedded in the porcelain when heated to high temperatures.
American raku
American raku is rapidly fired, removed from the kiln while hot, and usually smoked afterwards. A still red-hot piece is placed in a container or pit with combustible material and covered. Since the oxygen supply to the resulting fire is cut off, the piece receives a very heavy smoking or “post-firing reduction”. Many interesting glaze and surface effects can be obtained using this method. While “modern raku” is related to Japanese raku through the adaptation of the technique, the aesthetic of most contemporary work is totally unrelated to traditional Japanese work.
Firing process
If in firing porcelain, a piece of ware had to be supported in the bisque firing, it will stand alone in the glaze firing. The lower temperature will prevent sagging.
Testing the kiln atmosphere
Sometimes a kiln may be reducing only slightly and it is difficult to tell, because no flame is visible in the flue. Try this: hold a strip of newspaper in front of a freshly opened spy hole. If the paper just burns or gets sucked in towards the spy hole, the kiln is oxidizing. If the paper is blown out and away from the spy hole, the kiln is reducing. Try different damper settings to get the effect you want. Warning: Reduction firings create carbon monoxide, which is a deadly gas, and must be done in well ventilated areas, preferably outside. Do not try wearing a gas mask with a gas filter as compensation—the carbon monoxide molecules are so small that a gas filter, - even a good one - will not hold it back. Drowsiness and loss of concentration area signs of beginning carbon monoxide poisoning.
Don´t over-pack
When loading your kiln, do not pack it too full. It is a bad habit to stack things inside of each other, on top or in any combination to save space. Too much of this and the stress caused may result in cracked bisque.
Suggested firing guide: Stoneware gloss oxidation
Suggested firing guide: Stoneware gloss oxidation
1280-1300c (cone 10)
150c per hour up to 1280-1300
Firing Raku Copper matts
Copper matts are the most difficult raku glazes to fire consistently. To get the rainbow colors characteristic of copper matts, the glaze must first be reduced to metallic copper and then re-oxidized slightly. The final effect is similar to the halo created by heating a piece of copper with a torch. There are many different schemes for firing copper matts. The most common is to pull the piece from the kiln hot, smoke it as usual to reduce the copper, then let it re-oxidize while it cools in the container. When removed from the container, the piece is usually quenched in water to stop the re-oxidation.
How to fire
When firing China paints, you should vent your kiln on low and medium heat settings and close the lid when turning to high.
Sagging times
The length of firing time for glass sagging is less than ceramics. Place an 015 and 014 cone in your kiln in a pat of clay and fire until the 014 is halfway down, turn off the kiln and cool slowly.
S Cracks
One of the most common cracks found in pots is the “s” crack, which occurs at the bottom of a pot, in the shape of an s, usually on thrown pieces. I have heard so many theories about this and how to prevent it, that I am not even getting into it now. Perhaps later I will do a whole tip on the different theories so you can decide for yourself! The one thing everyone agrees on is that you should keep the bottom of the pot as dry as possible while throwing, and compress the bottom during throwing and trimming.
Expansion and contraction
Expansion and contraction of the kiln during firing will eventually cause the case of the kiln to loosen. To prevent this, the clamps on the jacket, lid and bottom of the kiln should be tightened occasionally when the kiln is warm.
Troubleshooting:Electric Mid firing cycle failure
If your kiln stops heating during a firing be sure to check your fuses or circuit breakers first. Be sure you know what fuses or switches control your kiln and how to replace them. A blown fuse or tripped circuit breaker is not necessarily an indication of an electrical problem in your kiln or wiring. If, your kiln heats in some switch positions, but not in all, you may have a blown fuse, defective element, switch or element connection which can be corrected by replacing a fuse or resetting a breaker. Be sure to locate defective parts if necessary and replace. If you think you have a problem inside the kiln during the firing cycle turn it off and allow to cool before opening. If you have a hot plug or outlet, one or both may be defective and should be replaced if they are too hot to hold. Do not re-fire until fixed.
Popular Cone Values
Popular Cone Values for Most Clays
For Bisquing Earthenwares Cone 04
For Glazing Earthenwares Cone 05
For Bisquing Stonewares and Porcelains Cone 06 to Cone 04
For Glazing Stonewares and Porcelains Cone 4-10 -See Clay Body Description For Specific Cone Range.
Loading: Glaze
Avoid crowding glaze pieces, as some have the tendency to ‘flash’ or ‘spit’ during firing and may leave a spot of unwanted colour on another of your pieces.
Maturing ceramic bodies
Most ceramic bodies have only one exact point at which they will mature properly. There is no way that you can control or guarantee the kiln being turned off at just the right point, except by using the proper cone and watching it closely to protect your ware.
Exposure to smoke
Try to avoid smoke when firing raku. The volume of smoke can be greatly reduced by placing one piece in each can and quickly covering it. When using newspaper as a combustible, avoid colored print. The colored inks contain heavy metals that may be carried off in the smoke. People with asthma or other respiratory sensitivities should probably avoid raku altogether.
Temperatures
Glazes and clays mature at different temperatures and may vary from company to company. Always check the container or package for the recommended firing cone.
Description
In a reduction firing, the oxygen supply to the kiln chamber is restricted, resulting in a saturation of free carbons in the kiln atmosphere, mostly in the form of carbon dioxide and carbon monoxide. In a strong reduction firing, flames will lick out of the flue and through other openings or cracks in the kiln walls. This is because the flame needs oxygen to burn, so it will try to get it from wherever it can. The reduction cycle generally begins between 1600o-1900o F (900o - 1000o C). Typical reduction glazes are ´copper reds´ and ´shinos´.
A ‘limit timer’ is the term used for the timing device that may be installed on a kiln to shut off the power at a predetermined and set time.
Firing time is important
A slow firing is always preferable to a fast firing.
The heavier a kiln is loaded the longer the firing cycle.
Suggested firing guide: Stoneware biscuit
Suggested firing guide: Stoneware biscuit 1000c (cone 06) 100c per hour up to 600c, then 130c per hour up to 1000c.
Suggested firing guide: Earthenware biscuit
Suggested firing guide: Earthenware biscuit 1150c (cone 2) 100c per hour up to 600c, then 150 per hour up to 1150c A relatively high biscuit temperature is used with this clay body to reduce the incidence of crazing in the glaze while retaining the clay’s porosity. Other clays may benefit from a lower biscuit temperature (1120-1140c) depending on their maturing temperatures (check the bag).
Technique
Pit Firing
Early cultures found clay in the ground and must have discovered its plastic and fired qualities by accident, probably discovering some burnt clay in a camp fire. This very basic firing then evolved into the pit-firing. Pit-firing involves placing unfired or bisque fired pottery in a pit in the ground, then covering the pottery with suitable burning materials, e.g. dried grasses and branches. Depending on the amount of work to be fired, a pit of the appropriate size is dug. A bed of dry leaves and twigs and possibly coal, which will burn slowly, is placed at the bottom of the pit and the pottery placed on top of this. The work is then covered with more leaves and twigs and dung, if available, building up a mound over the pieces. Once the stacking process is finished, the pile can be lit around the edges and left to smolder for several hours, if not until the next day. Towards the end of the burning process, it is possible to bury the pit in earth or sand, which will cut off the oxygen supply and create a strong reducing atmosphere inside the mound. Not all clays are suitable for such a firing, especially the more refined types available from suppliers. Additions of grog ´open up´ the clay and make it more resistant to heat shock. Clays dug directly from the earth may be suitable ´as is´, or might profit from additions of grog or volcanic ash, which also resists severe temperature differences. If using a commercial clay, get a clay suitable for raku firings. The best color results can be achieved with iron bearing, or red clays.
Mixing oxidation and reduction
Sometimes a firing cycle for a particular glaze (e.g. a ´copper red´) will include various stages of oxidation and reduction. Re-oxidation brightens up a glaze, although the effect will usually still be different from a pure oxidation firing. Re-oxidation is often done towards the end of a firing cycle, in order to eliminate excessive carbon trapping, which could result in dullness.
Dunting: Silica inversion
Dunting can occur as you cool through the first silica inversion at 1063 degrees F. At this inversion the body contracts suddenly. The more silica (quartz) in the body, the more contraction. Since different parts of the pot reach this temperature at different times, it doesn´t all contract together, and that causes stresses which can crack. Take for example a tall pot. The top will cool much faster than the bottom, because the bottom has the whole temperature of the kiln shelf keeping it warm. So the top will cool faster than the bottom, causing a crack around the bottom wall. Dunting can also occur as you cool through the 439 degree F inversion. A similar thing happens as above.
Cones: which one
Always use the proper cone. Do not try to get by with one that is close if you are out of the proper one.
Dunting:Thermal Shock
Dunting can occur months or even years after firing. For example, a pot might split right in half after 3 months. This is likely the result of thermal shock. In this case the clay and glaze expand at different rates when exposed to temperature variation, and this change causes the object to crack. To be more specific, the body has contracts more than the glaze. If the glaze is weaker it will shiver (see above). If the clay is weaker the object will crack.
Cone Use
Cones are slender pyramids composed of ceramic materials used to determine the combined effect of temperature and time, which is sometimes called ‘heat-work’.
Clays and glazes are fired to different points referred to by their cone equivalent or number.
Read the labels
Some manufacturers have special requirements for firing the glazes they make. Be sure to check the bottles of each colour for the proper cone.
reduction firing
A reduction firing is an incomplete burning where smoke and soot (the excess carbon) rob the clay body and glazes of part of their oxygen, thus changing their colour and texture. This is primarily a firing technique in pottery.
Ware and your electric elements
It is important that you do not let any ware touch the elements of the kiln. You may not only damage the elements themselves, but you are sure to damage your ware.
History
Black Firing Amongst the ´primitive´ firing techniques you will find the technique of Black Firing. This method involves heating a primitive gas-brick kiln to about 1000oC (these days with gas) and then adding copious amounts of sugar, which then volatilize and impregnate the clay with carbon, giving it a matt black surface. Glazes may also be used with this method, which can result in some interesting effects. The required temperature is usually reached in about five hours. The gas is then shut off and flue and any cracks sealed. Sugar is pushed into the burner port and volatilizes. Then the burner port is quickly sealed with bricks and fire clay. The kiln cools slowly and can be opened the next day.
Thickness
Thickness of the piece.
Air has to penetrate through the entire thickness of the piece and the gases have to escape the same way. It takes longer for carbon to burn out of a thicker piece of ware.
Use of cones
If you use cones for firing that need to be mounted in a pat of clay and placed in front of a peep hole you might find a cone holder designed for that purpose easier to use.
cracking: Even glazing
A thick layer of glaze on the inside of a pot, and a thin or no layer on the outside will cause stress. The result is often a spiral crack up the sides.
If glaze pools on the inside of a pot, tension is created and the pot may crack or split across the base.
Over glazes on porcelain
You can fire overglazes directly on porcelain bisque but you may have to use a hotter cone. These overglazes can be applied directly and fired in the 017-015 range.
Kiln care/floor
If the floor of your kiln has some rough spots caused from chipping off glaze drippings you can patch it with a special cement. You may also want to place an extra shelf in the bottom for protection.
Wadding for even shelves
If the kiln floor becomes rough and the shelves are difficult to keep level or steady, try putting small wads of clay under each post until it rests solid.
Prevent glaze on stilts
To avoid getting a big pile of glaze on stilts, try coating them with kiln wash.
Use cones
Use witness cones in the kiln even if you have an electronic controller or kiln sitter. This will show you the temperature that was actually reached inside the kiln (heat-work). See my article: ´(Orton Standard)Temperature Chart ´ at http://www.ceramics-tips.com/RscArticleV.asp?id=369
Cone care
If cones are exposed to moisture during their life, they may crack and bend prematurely when fired.
If you have problems with cracked cones because they become damp, drying them will not correct the damage. Use another box. Always store cones in a dry place.
Refiring on stilts
If you are going to refire a piece of glazed ware, but are having difficulty making the stilts stick to the bottom, try glue. The glue will not effect the piece and fire off.
Firing cast ware
The average cast piece may be fired on a fast firing schedule. Slow firing of heavy pieces reduces danger of breakage and many people feel that slow firing produces better ware.
Modern raku
Modern raku is a method of firing pottery loosely based on a sixteenth century Japanese technique. The Japanese would fire tea bowls in a small wood-fired kiln and then remove the bowls from the kiln with tongs while still hot and rapidly cool them. The thermal shock would crackle the low temperature lead glaze. Raku ware was preferred for the tea ceremony because of its soft feel and unassuming, quiet aesthetic.
tile setters’
Did you know that ‘tile setters’ are racks used to fire tiles to keep tem from warping during firing?
Grinding pots
Sharpening stones can be put to great effect by using them to grind off by hand left over bits of grog or alumina on the feet of pots and bowls or other surfaces.
Electric kilns, start on low
The kiln should always be started with your switches on low regardless of the type of firing. This reduces shock and dispels moisture from ware slowly.
Firing Larger pieces
Larger pieces that take all of the kiln dimensions should be placed so that the projecting edges are between coils.
Colour Maturity
Colours mature at a lower temperature on ceramic pieces than on porcelain or hard china.
Soda Firing
Soda Firing
The soda or vapor firing is similar to the salt firing, except that the salt is substituted with sodium carbonate (soda ash) or sodium bicarbonate (baking soda). The sodium (bi)carbonate delivers the necessary sodium for glazing, but the effect is much weaker. Often the interiors of pots do not glaze well, so extra glaze may need to be applied. But as carbon is additionally generated, instead of hydrochloric acid, this is an evironmentally friendly alternative.
Description
Woodfiring has an age-old tradition in ceramics. The very first ceramics ever fired were done (probably accidently) in camp fires and rudimentary kilns thousands of years ago. Under woodfiring we now understand firing a brick kiln with wood as fuel. This necessitates a a certain kiln contsruction type, sometimes with several burning chambers and stoking ports for feeding in the wood. As the wood burns, ash is created which deposits itself on pots in the kiln, creating a natural ´wood ash´ glaze. These natural glazes are made from silica, potash, calcia and other various ingredients that form naturally in the burnt wood.
Under-firing
Underfiring an overglaze will prevent the glaze from becoming soft enough to receive the colour, thus causing poor adherence.
Reducing warpage bisquing flatware
Items such as plates and tiles often warp less if bisqued on their side. You can lean them against the side of the kiln.
Silica for porcelain firings
Did you know that ‘silica’ or flint is a mineral which will not harden at firing temperatures and is used for separating porcelain pieces during firing?
loading a new glaze
If firing a new glaze you are unsure of, put the whole piece on a piece of bisque you have pre-made. Then if glaze runs, it will run onto this piece instead of ruining your kiln shelves.
Electric Kiln troubleshooting
If it takes longer now for your kiln to fire, It could be caused by a defective switch or element, or may even be the wall receptacle. If your kiln will not heat, the power cord may not be plugged in, fuses or breakers blown, kiln sitter not activated or power cord blown. If when firing, your wall receptacle or plug heats up, check to see if there is a loose connection in the receptacle. If a kiln makes popping noises when firing, it is normal. This is due to the contraction of kiln parts which are enlarged from thermal expansion.
Plate holders insure even firing of china painted plates
Plate holders insure even firing of china painted plates
Dunting Description
Dunting is a special type of crack which occurs from stresses caused during firing and cooling. These stresses primarily occur during two critical points of firing called silica inversions which occur at 1063 degrees F (573 degrees C), and 439 degrees F (226 degrees C). At these inversion points, the structure of the silica molecules rearranges. It is important to fire slowly through these two temperatures, and electronic kiln profiles often do this for you automatically while they are heating. Most dunting however is caused in cooling. These cracks appear as long, clean, body cracks with sharp edges. If the ware is glazed, the glaze edges are sharp. They may be vertical, horizontal, or spiral.
Warped ware
Warped ware can be caused by distortion upon removal of the piece from the mold, being fired too close to the elements or firing a piece in an unnatural position.
Pyrobars
Pyrobars serve the exact same function as Junior cones in the Kiln Sitter, except Pyrobars aren´t tapered and provide a more reproducable firing.
Clays
Flashing colors are typical of woodfiring, usually where a reduced atmosphere has been use in the higher temperature ranges, followed by an oxidised cooling. The flashing colors are very dependent on the nature of the clays used, and generally low iron clay bodies fluxed by felspars produce an orange coloured flash....
Read this great article by Owen Rye, prominant Australian Wood-firer: Woodfired clay bodies
Bisque
It may help when firing reds/yellows/oranges, to fire your bisque hotter than usual, to burn out more carbon during the bisque firing.
Firing Bright Reds/yellows
Oxygen: Most commercial glazes and underglazes are designed for use in an oxidizing environment (usually in an electric kiln.) Red, orange and yellow are particularly sensitive to the amount of oxygen in the air. All clay has carbon in it, much of which burns out in the early stages of firing. This creates carbon monoxide, which will af
