The slump mold is a great way to make bowls without using a pottery wheel or using the pinch-pot method. The molds are super super easy to make and well worth the time.
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Step 1: Materials Neeeded
You will need:
Pottery plaster. It HAS to be ceramic grade, otherwise it will dissolve in water very easily. (please wear a NIOSH mask when working with dry plaster. Avoidance of lung cancer is so very worth it...),
A non-important bucket,
The objects you want to make the mold from (must be flexible plastic, unless you want to cut it up to get your mold out),
A spray bottle of vinegar (not pictured),
Something to stir your plaster with.
Step 2: Mix Your Plaster and Pour
Mix your pottery plaster (you did get pottery plaster, right? NOT the cheap stuff from the craft store?) according to the directions. If there are none, it is usually about 1 lb of water to 1.5 lb of plaster mix. This is where the scale comes in...
This stuff sets pretty quickly, so use your stick to stir stir stir and get all the lumps off the bottom as quickly as you can and then pour it into the molds.
Give the mold a couple of good taps (not hard enough to spill the plaster) on a sturdy surface to get any bubbles out from the bottom.
I used 1.5 lbs of plaster and was able to make one good sized mold and one rather shallow one.
Step 3: Remove Bubbles
If bubbles bother you or you are planning on using all sides of the mold, spray the mold lightly with the vinegar to pop the bubbles.
Step 4: Wait, Wait, Wait and Then Remove the Mold
I would wait about 3 or 4 hours when pouring a mold as thick as the tall one in the picture. If the day is wet, you can wait longer.
Gently tap and wiggle the mold out of the plastic.
When it is out, you can lightly and very very gently sand or rub out any imperfections. But as long as you are not pressing your clay on very hard, you probably won't pick up the divots that may be left in the plaster.