I have always done it this way!

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If you are a potter and have gotten away with pushing the limits in your process for many years there will eventually be a day of reconing. That day could even be retroactive!

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For every mile of highway there are two miles of ditch! If we compare ongoing production of ceramics to a highway, then many potters spend some time in the ditches with troubles. It is hard to accept a kiln load of warped, bloated, dunted or crazed ware or a drying rack of cracked pots.

Potters can be hard hit and others go bankrupt when unable to solve a problem. If you think you have a process or a clay body that enables breaking the rules, think again. Your margin for error, which prevents problems, is narrower. The nature of ceramics is that if you do your best and suppliers do their best there will still be problems because of variations you or no one can control.

Consider some viewpoints that can get you in trouble:

I've always done things the same and now there is a problem, it is not my fault
Have you really always done it this way? Are there changes you have overlooked? Is the way you have always done it the best way? If you have been "driving on the shoulder" by taking shortcuts in the forming, drying or firing process then is being in the ditch a surprise? Is it possible that no supply company can deliver the kind of consistency that your "push-the-envelope" process requires?

We are too busy, we don't have time to change our process
By understanding details of the process and optimizing accordingly industry has figured out how to fire ware in less than an hour cold-to-cold. Maybe you could analyze your situation and solve the problem and cut time. It is often better to work out the problem than start over with a new clay body. Of course, there are times when switching bodies is needed.

I'll worry about making the ware, the clay manufacturer can worry about keeping the clay consistent
First, are you paying due attention to 'making the ware'? Does your kiln fire evenly? Do you really know what temperature it fires to? Do you stress ware during drying? Do you stress test your glaze to make sure it won't craze and pieces won't crack on sudden heating or cooling? Clay body manufacturers cannot afford to take the view that material suppliers have everything under control (although some do), constant material and product testing is a must.

I don't need to know that technical stuff, just give me a good clay and glaze recipe and I'll do the rest
'Doing the rest' involves a lot. No the least of which is being sure that a glaze from one manufacturer fits the body made by another. Good bodies and glazes need a good process to make them work.

I've been potting for 20 years, I know what I am doing
Old habits die hard and can bring trouble. 50 year potters are much less certain about things. Depending heavily on a traditional but shaky technique will bring a day of reckoning.

Feedback on a social media site verified this is my problem
Hmmmm

My glazes are crazing, they never did before
Glazes craze because their thermal expansion does not match the body. There is a lot of bad advice on this online, don't follow it. Any amount of crazing indicates a big problem. Lower the thermal expansion of a glaze or raise it in the body. Imagine realizing that all ware sold in the past is all going to craze for customers!

Understand the tradeoffs of your body and process? For example, vitreous bodies tend to warp or bloat on overfiring. Highly plastic ones tend to crack on drying. Porous functional ware bodies leak if the glaze does not fit. Low-silica or high-feldspar glazes often craze. Etc. Understanding your clay body and being in contact with the manufacturer is good. We are all going to weave on the one-way highway of ceramic production, but if you are near the middle you will stay out of the ditch.

Related Information

I have always done it this way. Why is it not working now?

Are you really sure the problem is with the materials? I had been using an 85% Ravenscrag, 15% frit glaze for many years with no crawling problems. But then it started crawling. I tried mixing with new materials and the old ones. Still crawled. The problem? What was I thinking? An 85% clay glaze is going to crawl so the question should have been: How did I get away with it for so long? I actually do not know! But I am now calcining Ravenscrag Slip as appropriate and I love the control this gives me in balancing slurry properties with drying hardness.

This always worked before. Why cracking now?

This thrown piece has thin walls and a thick base. A thickly applied inside glaze. No glaze on the outside (showing off the beautiful red body color). These factors are a recipe for glaze compression failure. And that is what has happened! But this has worked for the potter in the past! So what is needed to continue doing this unrecommended technique and get away with it? Thicker walls. Thinner base. Thinner glaze application on the inside.

By Tony Hansen
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