Substitute for hot waxing

 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.)

Glaze positioning

Leave at least 1/2" between all pieces when loading your kiln. Remember that the piece will expand during the firing cycle before it contracts and shrinks.

Firing reds

The red family of glazes is easily contaminated and requires more venting and a faster firing schedule.

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.

Bisque firing

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.

Bisque firing schedule-electronic kilns

This is a typical firing schedule for a bisque firing in a electronic kiln.
Segment 1: 80 degrees / hour to 250 degrees F
Segment 2: 250 degrees / hour to 1000 degrees F
Segment 3: 150 degrees / hour to 1300 degrees F
Segment 4: 180 degrees / hour to 1685 degrees F
Segment 5: 80 degrees / hour to 1928 degrees F.

Loading the Electric kiln

It is important to remember that one element groove must be between every shelf with the exception of half shelves.

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.

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.

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.

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 1/2 " 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.

How to do a Pit-Firing

How to do a Pit-Firing
This is the sort of thing you can easily do in your own backyard (subject to local council regulations of course). It´s a simple firing technique used in many ancient cultures across the globe and popular with potters today.
Here´s How:
Dig a pit of the appropriate size, depending on the amount of work to be fired.
Place a bed of dry leaves and twigs and possibly coal, which will burn slowly, at the bottom of the pit
Place the pottery on top of this.
Carefully sprinkle oxides and carbonates around the pieces (particularly copper carbonate), which volatilize and result in flashes of color appearing on the fired work.
Cover the work with more leaves, twigs and dung (if available), building up a mound over the pieces.
Once the stacking process is finished, light the pile around the edges and leave to smolder for several hours, or until the next day.
Towards the end of the burning process, bury the pit in earth or sand, which will cut off the oxygen supply and create a strong reducing atmosphere inside the mound.
Allow the kiln to cool overnight and open the next day.
Remove excess scum with a wire brush under a running tap.

Tips:
Additions of grog or volcanic ash ´open up´ the clay and make it more resistant to heat shock.
The best color results can be achieved with iron bearing, or red clays.
Bisque firing the work first helps to prevent shattering and cracking.

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!

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.

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.

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.

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.

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.

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.

Firing lustres

If you should happen to get broken, wiggly lines on your piece after a gold firing you may be over-firing.

Stacking for bisque

Items may be stacked on and inside one another for bisque firings. They won´t stick together. However, you can cause problems by doing this.
* The carbons may not burn out completely from an area that is covered by another piece, and this may cause defects during the glaze firing.
* Some items may break if they are not allowed to expand and contract freely. So if stacking two bowls for example, make sure there is plenty of room between them. Remember that items will shrink during firing.
* Stacking may cause more uneven temperatures throughout the kiln.
* Some people think the tighter they stuff the bisque load, the better. And you may have success with this method. But other people find that they do better when pieces are given space. My advice is that you can pack a bisque load tighter than a glaze load, but don´t overdo it.

Approx cone temps for bodies

Cone 022 10850F Lusters
018 1238 "
06 1840 Bisque, low fire glaze, raku
01 2030 Earthenware
1 2057 "
5 2156 Stoneware
10 2300 Stoneware, porcelain
12 2390 Porcelain
The numbers go higher and lower, but this is the range most commonly used.

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.

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).

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.

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.

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.

firing jewelry

A bisque tile can serve the same purpose as a shelf when firing jewelry or other light pieces

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.

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

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.

Repairs

Many repairs on your kiln can be done by removing and old or damaged part and inserting a new one.

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!

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.

Protecting the base

You can protect the bottom of your kiln by placing a full shelf there and coating it with kiln wash.

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.

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 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.

Large flatware

Items such as large plates benefit by being in the center of the shelf for even heating. This helps reduce warpage.

Changes in firing

All clays and many minerals contain water which does not leave the body until above 700°F. Organic (carbon) materials need to be oxidized (burned out). Other minerals, such as calcite, break down and give off a carbon dioxide gas. Minierals such as flint (silica) undergo a sudden expansion on heating to 1060°F and contraction during cooling.

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.

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.

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

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.

Time

The amount of kiln furniture you use in loading a kiln will effect the firing time too.

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.

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.

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.

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.

lid of your kiln does gap

If the lid of your kiln does gap in front, loosen the hinge screws a half turn when the kiln is hott. This allows the lid to reposition itself thus compensating for heat expansion. After repositioning, retighten the hinge screws.

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.

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.

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.

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.

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.

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.

refire a glazed piece

If you plan to refire a glazed piece and need to stilt it, coat the bottom with a light coat of clear glaze. This will give the bottom a texture and keep it from slipping of stilts.

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.

Holes in lace or fabric which appear after firing

Holes in lace or fabric which appear after firing, can be avoided by first washing fabric thoroughly before dipping into slip. Apply enough slip to the fabric so the clay will be strong enough to hold its own weight. The fabric must burn out before the clay matures, leaving only the clay shell.

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.

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.

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.

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.

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.

Limit timer

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.

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.

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.

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´.

For Bisque

Make sure your pieces are dry before loading them into the kiln. Pieces that are still wet will feel cool when placed on your cheek. Wet ware can blow up in the kiln, as the water inside the clay expands.

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.

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.

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.

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.

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

Prevent glaze on stilts

To avoid getting a big pile of glaze on stilts, try coating them with kiln wash.

Recognising Different cracks

If you have a crack, find the point where it is largest (widest). This will be the point where the crack started, and can help you understand what happened. Cracks in the rim usually were caused by stresses in the raw stage. Cracks in the base usually occur in the firing. Another way to determine the cause of a crack is to look at the surrounding glaze. If the glaze at the end of the crack is sharp, it cracked in the later stages of firing, probably during cooling. If the glaze is round at the edge of the crack, the crack probably occurred early in firing and the glaze had time to heal over. Remember that most cracks occur from stresses that occur during drying, even if they don´t show up until later. But some cracks occur because of firing and cooling, so it is usually best to fire and cool slowly.

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.

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.