Fort Pottery Company - clays, pottery supplies, and equipment

Over 1500 quality clay and ceramic products for hobbyists, teachers, and potters.

FAQ

Clay Faults
In general, most commercially prepared clays have been formulated to be used under demanding working conditions. When problems arise such as cracking, bloating, etc., our first response is to blame the clay we're using. Unfortunately, in most cases, this is incorrect and all too easy a solution. On the contrary, most problems arise through changes in the finishing stages rather than from the prepared clays themselves. In many cases, if the problems just started occurring, chances are that we started doing something a little different. The question is...What?
Another point to make, as a general rule, all clays have working properties which when pushed will yield problems. The solution is to find a clay that works for you or modify your technique to work within the working range of the clay. Remember, there's always a solution and we all have problems at some point.

Fault	Appearance	Cause	Suggested Remedies
Bloating	Bubble formation within body during firing.	1. Expansion of body produced by pressure build up of gasses trapped in a partially fused mass. 2. Over firing or irregular firing 3.Carbon trapped within vitreous body. 4. Body too high in flux.	1.Reduce firing temperature. 2.Fire more slowly. 3.Reduce flux content of body and/or add grog to open up body.
Blow Out	Craters in biscuit body	1.Presence of impurities in clay or glaze. 2.Particles of plaster in body. 3.Sulphates and/or carbonates present in body.	1.Avoid possible contamination. 2.Remove any plaster from work area as particle mixed in body will expand with moisture when present in biscuit 3. Use more refined clays such as commercially prepared bodies.
Cracking	Cracks in biscuit ware and finished work.	1.Rapid or uneven drying of clay ware. 2.Clay of poor plasticity. 3.Blunt turning tools. 4.Firing body too fast up to 300 C. 5.Overworking of clay during making. 6.Uneven wall or bases that are thicker than walls of form. 7.Use of too much water or water left standing in base of pot while making. 8.Throwing clay right from the bag without wedging. 9. Improper construction.	1.Dry more slowly. Invert ware when of sufficient strength. 2.Increase plasticity of clay or use commercially prepared clays. 3.Use sharper turning tools. 4.Slow down initial firing rate. 5.Reduce handling time during making. 6.Make sure water is not left standing in bottom of your work. The use of plaster bats will help aid in absorbing water in the base in the drying stage which will yield more even drying. 7. If throwing clay right from the bag, turn clay on side opposite of the direction as it was prepared by the mfg. Clay that has been pugged, will have a natural spiral from this process. 8. Slip and score clay when attaching two separate pieces.

Other Commonly Asked Questions and Suggestions

Question: My clay is too hard or soft to work with. What should I do to fix this?

A clay body becomes fixotropic (hard) at some point after blending. White bodies such as porcelain sooner. Unless the bag was left open, the clay has not really lost moisture when the clay is at this stage. The clay simply needs to be shocked or loosened up to return it back to its original working state. Also, wedging clay is suggested prior to use. If the clay has not been used for a year or two and seems too hard to work with, simply place the bare block of clay in a plastic tote, drape a wet towel over it, and seal it up for a couple of weeks. Continue to add water to the towel to achieve the desired consistency.
If you find that the clay is too soft, simply open up the top of bag and let stand for a few days. However, you'll need to monitor this. Another great way to stiffen clay up is to use a plastic tote, just like above, but do not add a wet towel. The moisture will condense on the lid allowing you to easily remove the excess water by pouring it off.
If none of these suggestions work, you may want to consider custom blending to a better working consistency. There is an additional mfg charge for this and has to be ordered in increments of 1000lbs.

Question: My clay has mold on it. What's wrong?

Nothing. As clay ages, bacteria grows and begins to break down the clay particles making the clay more plastic and usable allowing it to be stretched and pushed farther. A general rule of thumb is the older the clay, the better it is. Newly prepared clay (also know as green clay) may tend to seem short and crack easier when bent or stretched. Many potters let their clay set for months or years before using it. You may want to keep a revolving amount that will allow for this aging process.

Question: My bags have not been sealed. Will my clay loose moisture more quickly?

This is an across the industry move to reduce one less step of the making of prepared clays and keeping the cost down as cost continue to rise on everything we buy. It has very little or no impact on moisture loss if stored properly. Clay should be left in the box before to use. Even with strapped bags, clay should be left in the boxes. Removing it from the original box will cause the plastic bag to separate from the clay and lead to moisture loss through water condensation on the inside of the bags.

Question: My clay looks darker or lighter in the bag from the last batch. Should I use it?

As clays change in the mines, colors change as well. In most instances, this is due to the additive Fire Clay that tends to change more drastically. Fortunately, if there is a slight appearance change in the color, you most likely won?t notice it after it has been bisqued and glaze fired.