My friend Karen had an interesting blog post today showing the sizes of same sculpture cast in resin, earthenware and bone china. Each of those materials has a different shrinkage, from next to nothing (resins) to quite dramatic (bone china).
What I found interesting was the level of shrinkage in her earthenware casting. It's quite a bit smaller than the original. My own experience has been that the size reduction on earthenware varies, but the range hasn't been quite that great.
Here are some pictures of a bisque Finn next to the resin original (with the mold lines drawn on). This represents the high end of the shrinkage I have gotten.
It would be interesting to compare slip recipes to see what makes the difference. In the past I've used shrink ratios to create smaller versions of an original. The only problem was that it took a lot of intermediate steps (an expensive rubber molds) to reach a significant change in size. I also found that you could get a "Xerox Effect"; slight changes in proportion early in the process could get compounded with each subsequent shrink, until the piece was visibly "off" in some way.
That's one reason why I have limited my shrinking experiments to medallions. Their mass is pretty evenly distributed, whereas full body horses have more variation (not to mention both solid and hollow areas). I feared I would get a lot more distortion. I wonder, though, if a clay with the kind of shrinkage Karen saw with her Optime might not alleviate that problem, since there aren't as many shrinks involved.
Hmmm... things to ponder while I paint! (I am telling myself NO experiments until I see a lot of colored horses on my workbench.) Oh, and I guess this post is also a sneak peek, since the Finn illustrating the shrinkage is for the lottery. I am hoping to get a color a bit like this Collier I did a few years ago, though greys often go in surprising directions before they are finished.