Tag Archives: slip casting

The translucence of porcelain rice grain ware

Bluish white porcelain with translucent spots the size and shape of a grain of rice. Clear glaze with light blue or bright cobalt accents. The first time I saw rice grain ware was in Montana in the form of a teapot. It was beautiful and exotic. I couldn’t figure out how it was made. If you hold it up to the light you can see through the tiny spots. I’ve read some sources that said it was made by inserting little grains of rice in the walls of a porcelain vessel. After glazing, the rice evidently burned out during firing, so all that was left was the translucent glazed area. As it turns out, it is created much more simply. No rice is used at all, states Jan-Erik Nilsson Gothenburg on his Gotheborg site. This makes sense because, as another source pointed out, the rice would expand by absorbing moisture from the clay as it dried, thereby growing in size. This would cause the vessel to crack before bisque firing. “‘Rice grain’ is a name of a technique rather than actual rice grains,”  according to Gothenburg.  “To make this kind of decoration the holes are pierced through the rather thick walls of the rough and unfired porcelain and the holes are then filled with translucent glaze.” Interestingly, the porcelain vessel is initially quite thick. After the holes are made, then filled with the glaze and dried, the potter reworks the vessel.  This is done by thinning the walls without compromising the integrity of the vessel. Surely this must not be how they are all made, however. It seems there must be a big market for slip cast rice grain ware, considering the amount that is sold. Pieces made the traditional way must be wafer thin. “The highly skilled potters, who are usually young women, after what I saw when I visited a factory for this kind of porcelain in Jingdezhen in the 1990’s – are judging the thickness of the walls and the work progress by the sound of the paring knife against the unfired clay,” writes Gothenburg. He says the technique came to China via Turkey in the 14th century. Another style of pottery is made when the holes aren’t filled with glaze. This linglung work creates a lattice effect. These techniques are much older than I realized and the oldest pieces are quite collectible. I myself have a modern rice grain ware teapot. Such porcelain is common and inexpensive in Metro Vancouver, so my take on it is that the finer pieces are pared thin by hand but, others, like my teapot, are slipcast. It is no less appreciated, though. The translucency makes it appeared delicate and the cobalt blue decorations enhance the whiteness of the porcelain. These pieces are truly beautiful.

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Making Slip for Slipcasting

This week at the studio, Otto talked about having made slip to use in plaster molds. A little piece he’d slip cast was on the work table when I came in. It’s been so long since I’d done any slip casting, it made me wonder what the ratio of clay to water should be, how it is made smooth enough to pour, etc. So, I found a couple of articles to share that concentrate on these aspects and more. I think the last time I did slip casting was with my Mom’s friend Nancy when I was seven or eight! Maybe it’s time to give her a whirl. Slip casting is a good article covering the process from start to finish and includes formulas. Basically, the ingredients consist of clay in dry form, water, water glass (sodium silicate). I’m a fan of allexperts.com and found some good information from one of their ceramic experts. He said, “any clay can be turned into a slip. Cut the wet clay up into small pieces and let it dry out completely. Put the dry pieces in a container and add water until it just covers the dry clay. let it sit, do not stir, you will be able to see the clay disintegrating as it absorbs the water. Within a few hours it will be ready, next day is better, mix up and use.” This is exactly what I wanted to know and I have some pieces I never bisqued for one reason or another. So, I think I’ll just break them up and follow Sam’s advice. Here is another site that gives good basic information. It is not an in-depth article, but covers the process of slip casting rather well. I cannot vouch for the veracity of the article, though, in terms of the length of time needed to mold a piece, because these articles have conflicting advice and I don’t know what to believe. Another article suggests 20-40 minutes, whereas the ‘another site’ article above says eight hours or longer, depending on the size. That sounds like an awfully long time. I guess I’ll just have to experiment and follow-up with Otto. I like the idea of slip casting something, then altering it to make it more of my own. Since a piece is leather hard when unmolded, I would still have the time to make changes. This video below on “Clay for the Slip Casting Process” gives more depth. Based on what this ceramist says, I would have to add a deflocculant like water glass or soda ash to make slip the right consistency. Also, I have to consider whether the clays I’m considering using are appropriate, a white and a red clay. According to the video, porcelain is a good choice. Because there are many questions still unanswered, I am going to have to ask the centre’s artist-in-residence more about slip casting to get a better idea and I will report what she says at a later time.

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