Archive | January, 2008

Impatience

I think ceramics is one of those fields that really favors patient people. My friends tell me all the time that I’m “very patient” – though admittedly they are usually making this comment after spending the day with me and my overly-exuberant youngest child. Maybe that kind of patience doesn’t translate to waiting for things to dry. Waiting until molds are dry enough to use, and until castings are dry enough to remove, is terribly difficult for me!

So there are victims. This poor Finn got pulled out of his mold before he was dry enough, and his side collapsed. Things like that just aren’t worth the time they take to fix, so I crumpled him up. Normally he would have ended up the scrap bucket, but I must have missed him when I was cleaning. I found him this morning. Doesn’t he look so sad? Actually, he almost looks like a horse all curled up to take a nap… if horses had no bones, that is.

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The finished product!

Here is the first of the finished “Windblown” plaques. I wasn’t sure how the plaque would turn out in an art glaze. It was really designed so that the horse would be glazed in a realistic color while the background would be finished with an art glaze. (The leaf texture is there to take advantage of how art glazes flow into the recesses of the design.) But I like the all-over art glaze after all.

The plaque also shrank quite a bit. I had already noticed that my current batch of slip had a slightly higher shrink ratio than past batches. Whereas before the shrinkage was negligible, the new slip (using the same recipe) had an overall shrinkage rate of about 6%. For some reason, though, this particular piece is shrinking around 9%. You can see the dramatic difference between the final piece and the first original here.

The finished one is actually one mold further from the original, since the mane was added to a casting from it, but that’s still a lot of shrink for one generation of moldmaking. It took quite a few generations of molds to shrink the Celtic Pony medallion that far.

I’m not sure why the shrinkage is so different from the pony. Perhaps the fact that it’s rectangular, or has less depth. Or maybe because it can be poured with thinner walls. The question does make me wish I had studied ceramics in school, rather than graphic design! But whatever the reason, it certainly will make reducing the design to ornament and then to pendant size easier.

In the meantime I will be learning this mold’s idosyncracies. They all have them! How thick the slip, how thick the walls, how long to leave the drained casting in the mold… each mold wants something different. So you always lose a fair number of castings from the early life of the first mold. The trick is to write all the preferences down so you don’t have to relearn it all the next time the mold gets used!

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