Originally Posted on: Aug/03/2005 16:52
I have recently started using Coleman Porcelain. Most of my work is handbuilt, carved/pierced and sagar fired. I know from past experience that you need to use a new clay type for at least a hundred pounds before giving up in frustration. Well I have gone though about 85 of those pounds and I am about ready to throw in the towel. But porcelain has such a wonderful finish, I would really like to make this relationship work. Hopefully there are some tips out there to save me.
First, there is a lot of cracking going on. I have learned to do the bulk of the carving/piercing while on the wet side of leather hard, leaving only fine detail for dryer clay. I have also learned to dry the work slower than slow and, most importantly, never let one part get wetter or dryer than another part. Still, I have cracks after sagar fire (2-3 hours to 1650 degrees hold for 1 hour.)
Second, it dries FAST. In the time it takes to join slabs and add the feet, handles, etc, for a large box, the clay is past the "wet side of leather hard" I need to carve. And my carving takes a few hours just for that step. How do I keep it wet, without cracking the (grumble,grumble)clay by spraying it.
Finally, I use porcelain for its lovely white, but I seem to get odd black flecks here and there. Sylvia Rassmussen was telling me this can be contamination from other clay on my tools or in the studio. Do people who use this clay really have a completely separate set of porcelain only tools? (Yes, I do want to know how deeply obsessive you have become!)
Thank you for any thoughts to save my sanity.
I to get the black spots occasionally. Some o it may be metal from the pugger at manufacturing, some from your tools, and from other clays in your studio. I work with all types o clays, and have found that I must inspect the work to check for perfect whiteness....and pick out the flakes.....usually so small I disregard them.
For the cracking....work wetter at the earlier stages....like when you are building....don't work at such a dry leather hard...this should help.
Other than that, you just have to keep it wet, with a spra bottle and sponge. I have ha no problems with cracking with my wheelthrown porcelain, or my sculptural forms....hve not done hard slab with it....too problematic. Just lik B-mix.
Try English Porcelain, it's alittle pricy but has a great texture, seems to stay wet longer, throws great. I bisque my pots to cone 05 and sagger fire (in a large brick box in side my kiln) until cone 06 bends. inside the box i'm only reaching a soft cone 012.
iwas told that richard notkin (very tight hand built stuff would make all the parts to a piece and then put then under a big bell jar over night. then he would assemble them. i have wraped some of my over dry pices in damp paper towels and put them in plastic bags.
Damp towels is a great idea.
I had a large carved tray dry wrong and crack. I wrapped it in damp towels to reconstitute the clay and was able to replair it. Funny how the answer can be right in front of you and you don't see it.
I think you just solved my problem. Thanks! -Dawn