02/22/2009 (10:46 am)
Square rice bowl press molds
In my last post I mentioned that I was going to pour some plaster molds to make square rice bowls. I found a really cool square bowl in the after-Christmas sales and thought, “Hmm. That would make a great rice bowl,” so I picked one up and brought it home. I spent a couple of days making the molds and documenting the process in pictures, and here it is!
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First, I gathered the supplies. This is very important because once the plaster is mixed, there is no going back! It will set up while I’m searching for things. Here you see the bottom and side boards (called casting boards) for the mold, clamps, the square bowl, clay, buckets, mold soap (really Murphy’s Oil Soap), and a paintbrush. |
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I clamped the casting boards together using the square bowl as a guide. I left about 1.25 inches of space around the bowl. |
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The next step was to seal the corners of the mold. I pressed coils of clay into the side and bottom corners. Without this seal, plaster leaks out of the mold and makes a huge mess.
I’m wearing latex gloves here because experience has taught me that plaster destroys my hands. It sucks all the moisture out and leaves them dry and cracked. |
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After all of the corners were sealed, I applied mold soap to the casting boards. This makes for an easy release of the boards when the plaster has set up. No need to soap the bottom board since it’s formica and the non-porous surface will release from the plaster easily. |
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See the writing on the plaster bag? It says breathing plaster is BAD FOR YOU. That stuff settles into your lungs and doesn’t come out. Same with powdered clay particles. That’s why it is important to have the right type of particle filtration mask. I wear it anytime I’m messing with the plaster bag or pouring dry plaster into the bucket for mixing. |
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The dry plaster was added to water, then mixed by hand until it reached the consistency of thick cream. I mixed slowly to try to avoid bubbles. The bubbles that you can see on the top of the bucket were scraped off and dumped in the trash.* |
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Next, the plaster was carefully poured into the mold. I use a smaller container to scoop and pour the plaster, and pour it over my hand to try to reduce bubbles. Once I had filled the mold, I set the bowl into it at an angle and bounced it up and down gently. Again, this was to try to get any big air bubbles to rise to the top. |
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I weighed the bowl down until the top was at the level of the plaster. I let it sit for 40 minutes or so, then removed the bowl and the boards. Plaster gets hot while curing, so I wait until I feel it starting to cool down before I remove the casting boards. |
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The mold after the boards and bowl have been removed. It’s ready to be cleaned up and set on a rack to dry. |
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I use a fettling knife to knock off all of the sharp edges. A word of warning - don’t leave damp plaster on your tools! It will set up hard as a rock and is hard to clean off. Speaking from experience here.
The final cleanup was a wipe-down with a damp sponge. |
One step I didn’t photograph was the cleanup. I have a small bucket with a plastic bag liner and as soon as I poured the plaster, I scraped the rest of it into that trash bucket. Then I gave my mixing bucket a quick wipe with a sopping wet sponge and poured that water into the trash bucket too. If you let the mixing bucket sit, the plaster will set up and be impossible to remove. The key is to have everything set up and to work fast.
*NEVER pour plaster or plaster water down the sink drain!! You’ll be sorry. And you’ll have an expensive plumber bill.
Altogether I made three molds and am happy with two of them. They’ll need to dry for a couple of days, then I’ll make some bowls and post the results right here. Stay tuned!
5 Comments »
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Hey Dina - that’s such an interesting post! I love the photos right along in the step by step text. I’ll probably never do this myself, but I enjoyed reading the whole thing. Can’t wait to see your end product.
Michelle
Comment by Michelle Dodd — February 22, 2009 @ 4:48 pm
Very Cool idea and I haven;t seen many square rice bowls. . . . Hummmm
Comment by mary starosta — April 14, 2009 @ 8:31 am
I am interested in how you shape the square bowls using these molds. Are you doing slab and if so, how to fit them into something this deep. Are you using sections and joining?
I recently thought about using something very similar in shape and depth to your mold. Did you ever post a followup after the molds were dry?
Comment by Kim Granade — November 21, 2009 @ 7:23 am
I am interested in how to use a mold this deep to form a bowl. I recently tried to do something like this with slab but had trouble trying to figure out how to fit the clay slab in the mold without tearing or folding. Did you post a followup for this? Are you using slabs in sections or do you have a technique that you can share?
Comment by Kim Granade — November 21, 2009 @ 7:27 am
Hi Kim,
Thanks for stopping by! I did not post a follow-up to the square press mold post. What I found is that it’s impossible to put a single slab of clay into the molds. There is just too much clay for the corners. Instead, I did some bowls with cut slabs, and others with torn slabs. Still haven’t fired those pieces, but will do soon. I will post my results on the blog. I’ll be around a lot more in the new year.
Take care,
Dina
Comment by dina — November 22, 2009 @ 2:50 pm