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Comment by Jan Wallace on September 3, 2012 at 12:55pm

Carl, I have been also using similar methods for rolling slabs. No stretching the clay by throwing anymore as I have heard that this can accentuate problems with warping, but by hitting with a pin, turning over and around and hitting again, then finally some rolling with the pin. Stretching te clay by turning and hitting this way, I am told, helps to remove the clay memory which can cause problems with warping in firing/drying. I have reduced warping but still get the odd plate that warps in the glaze firing (very frustrating). I have been drying my flat plates on a type of fibroboard to absorb water and also try to slow the drying a little. Recently I have been making larger childrens handprint tiles ( 25 x 20cm ) and had a few issues there with warping in the glaze firing too (arghhhh). Using a grogged clay (rec for tiles ) and only firing to 1100 deg c. but they were coming out a little concave (turning up around the outside edge). But I think I have eliminated that by glazing the bottom and putting on stilts. With my Cone 6 work and the plates, I tried to glaze the underside and put in stilts but they warped even more and slumped/dunted. As i said though, the clay I am using is earthenware and I am pushing the limits firing it to cone 6. With your idea of using the special made tile to aid your issue, I think that makes sense. I have been using a plaster mould made from pouring plaster into an old square icecream container which seems to have that shape naturally (dips slightly in the centre, turning up around the edge when looking at the mould) and I have found the least problems with warping when using that mould. It actually only occurred to me when you mentioned it, but it makes sense.  Using a sponge and rib on the back of the upturned clay and compressing when over the mould also has to help with assisting the clay to have new memory and prevent warping. As a pose to just placing clay over and hitting with a paddle. Hmmmm... I think we are getting somewhere :)

Comment by Carl Ray Crutchfield on September 3, 2012 at 6:25am

Jan, thanks for the encouragement; I was pleased with this one also.  I do have problems with warping.  I have read, asked, and experimented and still have not figured it out.  The larger the piece, the more difficulty.  so far what works best for me is ... I dry my pieces on 1/2 inch thick particle board bats and slow the drying process to at least 3 days with the use of plastic wrap.  I am careful to roll out my slabs by flipping them and roll in both directions.  I, like you, do not glaze the bottoms except for the turned up rim.  Even so, they often warp, if only sightly.  I have noted, for me, that the warping seems to remain the same from bone dry to bisque to glazed.  I recently made and fired a flat tile with a very slight intentional convex curve to the bottom and I am going to try pressing my trays onto it with a 2 inch thick sponge block as a last step before starting the drying process.  My though is that it will give the tray an ever so slight upward curve to the bottom of the tray in hopes of causing it to rest on the bottom edges just before the upturned rim.  I have also built and fired another tile that will assist me in putting feet on some of the trays in hopes that I will like that result:)  Sorry this is so long, but it is something I have struggled with repeatedly and have yet to find "The" answer.  I really like making trays and the opportunity to experiment with more painterly styles of glazing.  I have a show coming in December and what trays to be a large portion of my presented work, so..... if you have any revelations, please let me know.  Walk in peace, -carl  

Comment by Jan Wallace on September 3, 2012 at 3:33am

Hi Carl, Love you trays especially this one. Just a quick question. I have made a few similar things lately (square plates) and fired them to Cone 6. I leave the underside that sits on the shelf of the kiln unglazed but have had a few warp on me diring the glaze firing. They went into the firing perfectly flat. I think it is the fact that I am using an earthenware clay and firing it a little higher than recommended for glaze, so they come out of the kiln a little out of shape (unbalanced when on a flat surface). Or, perhaps it could be the thickness of some of my plates? Have you come across any problems with warpin? Thanks