You can use a plaster mold repeatedly.
Plaster molds are useful for recreating a carving or object exactly. Poured plaster press molds can be used to create latex masks, sprig--pieces of raised decoration that can be applied to pottery or other projects--or to create the same decorative tile over and over. With some preparation and concentration, poured plaster molds are easy to make and save a lot of time when creating multiple copies of the same element.
Instructions
Prepare the Object
1. Prepare the mold object for the plaster. If the object has any gaps on its lower side, where the plaster might flow under it, fill them in with clay. These are called undercuts, and if you don’t fill them in it will be much, much harder to get the object out of the mold.
2. Place the object in a tray with sides at least an inch higher than the object. You also want to have at least two inches of plaster around the object. You can use an old cooking pan or even a wooden box, as long as the edges are tight enough to keep the plaster from leaking out.
3. Spray the pan and the object liberally with non-stick spray, which will keep the plaster from sticking to the pan and the object. Some materials-such as leatherhard clay--don’t necessarily need this treatment, but it never hurts.
Mix the Plaster
4. Choose your plaster. Plaster #1 works well, as it has fine particles that retain detail well. However, plain plaster of Paris will work well, too. The mix ratio for most plasters is two parts plaster to one part water, but follow the manufacturer’s instructions.
5. Put the water into a bowl or bucket and slowly sift in the plaster mix. Once all the plaster powder is in the water, let it set for a minute or two and then mix the plaster slowly to avoid introducing air bubbles. You can do this with an electric mixer, but be sure to keep the blade deep in the plaster and away from the air.
6. Tap the bowl or bucket gently on the table or floor to bring air bubbles to the surface. If it’s too large to lift, you can smack the sides to achieve the same end. Once the bubbles have risen, use a spray bottle containing rubbing alcohol-just one or two spritzes-on the surface of the plaster. These will disrupt the bubbles' surface tension and get rid of them.
7. Test the plaster by drawing a line in it with your finger. When it’s thick enough that it doesn’t fill in right away, it’s time to pour.
Pour the Plaster
8. Coat the object with a thin layer of brushed-on plaster and let it set for a few minutes. This will prevent any air bubbles that form from working their way to the surface you’ll be using as a mold.
9. Pour the plaster into the tray or box, over your object. The biggest problem to worry about at this stage is that you might introduce air bubbles into the plaster. Pour slowly and let it run over your palm if you need to slow it down further.
10. Fill the tray or box until there’s around two inches of plaster over the object. This is important, because a thick base will keep the mold from cracking and help hold it together.
11. Tap the tray or box against a table to bring air bubbles to the surface. You can use the spray here, as well, to get rid of any air bubbles.
12. Allow the plaster to dry until it’s hard but still soft enough to carve. It can take a while for molds, especially large ones, to dry completely, but they’re usable as soon as they’re hard.
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