Frozen Clay??

[Barbara Howe]

Hello! Has anyone out there had any issues with frozen clay? We moved from the north of the province to the south and I had too much clay to pack in the vehicle so it went in the moving van and froze. I wasn't too concerned - I have a Peter Pugger. After a series of challenges I finally got my new studio set up and went to work. I noticed nothing unusual, except that the clay seemed a bit less plastic when I was pulling handles. The bisque load seemed fine as well. Just unloaded the glaze firing. Seemed ok until I pulled out a sugar bowl. The top of the nob was very rough. I thought this odd. The same was true for the casserole nobs. When I looked at the unglazed bottoms I could see many tiny bumps - kind of like very fine goose flesh. This is very disconcerting as I have another load thrown and ready to go into the bisque. The only other thing that was added to the clay is a small amount of epsom salts to increase plasticity. Expertise? Thoughts? Anyone? All help would be appreciated.

[Pat]

Hello - Did you find an answer to your problem? I am curious about how your next load turned out. I have had lots of clay freeze on me and other than having to do a little extra wedging it was no worse for the ware. Where did you source your clay and what type of clay body was it?

[Barbara Howe]

Hi Pat. It seems that the problem had more to do with soluble salts leaching out of the clay and not getting burned off. A subsequent load was worse, with little white blobs on the tops of casserole dishes. I have decided to bisque to cone 04, instead of 06 and have also decided to switch clay bodies. I was using a porcelain clay (P300) and have switched to one from Tucker's clay in Ontario. Just waiting for the first load to arrive. Pat said:

Hello - Did you find an answer to your problem? I am curious about how your next load turned out. I have had lots of clay freeze on me and other than having to do a little extra wedging it was no worse for the ware. Where did you source your clay and what type of clay body was it?

[Pat]

Hi Barbara - I used to work a lot with high fire Grolleg porcelain and a cone 6 porcelain and have never had a problem with them freezing each winter. Your post sparked me to read about the issue and which will be helpful as I test new clay bodies. This article mentions that you can add 0.5% barium carbonate to earthenware bodies to combat issues with soluble salts http://lindaarbuckle.com/handouts/clays-and-clay-bodies.pdf . I don't remember enough about the chemistry end of things to know if this would be useful to try with the porcelain you have left. Being a fan of experimentation I would give it a whirl :)

Thanks for the quick response to my question!

Pat

[Barbara Howe]

Thanks Pat. I'll have a look at it. I have thrown a new load which I will bisque to cone 04 and see if that solves the problem. This world of mid-fire glazes is new to me to so I'm feeling my way around. the soluble salts bubbling to the surface was pretty unexpected. If the new cone doesn't do the trick I'll check out the barium. Hopefully it won't be necessary. Figuring out how to add the barium to a prepared body might be the trickiest part.

[Pat]

Mid-fire isn't my comfort zone either. I did find another site that had pretty extensive information about soluble salts in clay but the focus seemed to be on how to know if they are present not what to do if they cause problems. Maybe some searching online can provide you with a more knowledgeable answer to the issue.

Have a good day!

Pat

[Norm Stuart]

Barium Carbonate is the solution for clay with soluble salts, rendering them insoluble.

Commercial clay vendors add just enough barium carbonate to their clays to prevent efflorescence, typically in the range of 0.1% to 0.8%.

Efflorescence - Scumming

Barium Carbonate in Clay Bodies

Soluble Salts

The only other solution is to reconstitute dry clay with an excess of water, which is then discarded, hopefully along with a percentage of the salts present in the clay.

[Barbara Howe]

Thanks Pat and Norm. The solution seems tricky. Here's hoping the new clay body works better.

[Pat]

I am starting work with clay I have dug in my field and I am thinking Norm's fix of making a slurry, letting it settle out and pouring off the water is a good plan to preemptively combat the problem. You never know where you are going to run into useful, timesaving information. Thanks Barbara and Norm :)

Barbara I hope the new clay body serves you well. Happy potting!

Pat

[Norm Stuart]

There's a limitation to the effectiveness in removing salts from clay by pouring-off the water after making the clay unto a slurry. It only removes the salts already dissolved and those which readily dissolve.

The reason commercial clay suppliers also add barium carbonate is that many clay materials continue to release soluble salts over time.  This is particularly true when a high salt material like Nepheline Syenite is added to the clay to lower the maturity cone.

The slow release of these salts over time also cause glaze hard-panning (deflocculation) over time, which needs to be countered with the addition of calcium chloride (ice melting crystals) or magnesium sulfate (epsom salts).

Just being in contact with water can slowly leach additional salts out of the clay material, and this is accelerated by bacterial action — which is why commercial clay makers also add preservatives to clay.

Pat said:

I am starting work with clay I have dug in my field and I am thinking Norm's fix of making a slurry, letting it settle out and pouring off the water is a good plan to preemptively combat the problem. You never know where you are going to run into useful, timesaving information. Thanks Barbara and Norm :)

Barbara I hope the new clay body serves you well. Happy potting!

Pat

[Barbara Howe]

I hope your 'field clay' works well for you. Should be interesting!! The new clay has arrived. We'll see what happens!