Welcome to Ceramics Tips

Firing reds

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

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.

Loading the Electric kiln

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

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.)

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.

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

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 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.

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

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!

Repairs

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