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To mix your own glazes you need:
Typically one starts by finding a glaze recipe, from a book or a reputable web site. Start with a glaze recipe which is formulated for your particular firing type and clay body (ie Stoneware clay, fired in cone 6 oxidation.). Recipes are usually expressed in numbers that always total 100. For example:
Determine the amount a glaze you want to make and then add the appropriate ratios. For example, if you want to make 1000 grams of glaze, you would add:
After the glazes have been mixed (using a good mask, as many of the ingredients are toxic and should not be inhaled), water is added until an appropriate thickness has been reached. Potters often refer to this thickness as the thickness of low fat milk. I is a good idea to let the glaze sit for 24 hours before using, to make sure all the particle are fully wet. (Note, some believe it is better to add the dry ingredients to the water, instead of the other way around...)
At this point, the glaze must be sieved 3 times to ensure all the clumps are out and the glaze is perfectly smooth. To sieve a glaze, a sieve is put over a bucket. The glaze is then poured into the sieve and pushed through with an object such as a rubber rib. (for more information on mixing, see Mixing Dry Glazes.)
Pots are then dipped into the glaze, or the glaze is sprayed on.
First, put the glaze into the inside of a pot, swirl it around and let it run out. If the piece is extra thin, let it dry before glazing the outside.
Then glaze the outside of the pot, by dipping 1-2 times, or by pouring glaze over the piece. You can dip a piece in upside down without disturbing the inner glaze, as the air will keep the new glaze out. Finally, the piece is fired.
A good glaze is one that looks like you want it to, and in the case of functional ware is non-toxic and fit for it's purpose. If it has too much flux, it may run excessively all over the kiln shelves. If it does not fit your clay, it is likely to chip, craze (tiny cracks across the surface of the glaze), or shivver (clay shrinks more than the glaze).
If there is a good fit between the glaze and the clay body, the piece will be very strong. You can test the fit by alternating a pot between boiling and freezing water. If it is going to fail, it will then.
Otherwise you may find out months later that the piece is not holding up. If glaze defects occur, you will need to troubleshoot the glaze to determine why, and what it needs to correct it. There are software programs available to help you do that.
Links to websites with glaze recipes