How to Make a Positive Mold

Use positive molds to create crafts.

Most molds used in ceramics are negative molds in which you pour ceramic clay into a mold to produce clay objects. However, some projects require the use of a positive mold, also known as a slump or hump mold. You can make positive molds out of bowls or anything that will hold plaster. Once you've made the positive mold, you can build a sculpture or ceramic bowl directly on top of the mold. You then allow the item to dry until it is leather hard, then you remove it before it begins to shrink.

Things You'll Need

• Plastic bowl
• Clay
• Clay tools
• Plaster
• Water
• Large bucket
• Long, plastic cooking spoon
• Halloween mask
• Cloth-backed adhesive tape

Instructions

Positive Bowl Mold

1. Mix the plaster according to the manufacturer’s instructions in a large bucket.

2. Stir the plaster with a cooking spoon until you thoroughly mix it.

3. Pour the plaster into a plastic bowl.

4. Allow it to dry for 24 hours before using.

Positive Sculpted Mold

1. Create the hollow base shape that you want to use out of clay. You will be making a mold of the inside of the clay shape.

2. Mix the plaster according to the manufacturer’s instructions in a large bucket until smooth.

3. Pour plaster into the clay shape and allow it to set up. Once it is dry, peel off the clay and let it dry for 24 hours before using.

Positive Face Mold

1. Buy a Halloween face mask.

2. Tape the eyes and any openings with a cloth-backed adhesive tape on the outside of the mask.

3. Mix the plaster according to the manufacturer’s instructions in a large bucket until smooth.

4. Pour the plaster into the mask and allow it to set up.

5. Remove it from the mask and let it dry for 24 hours before using.

Tips & Warnings

• Positive molds can be used for other craft projects besides ceramics. You can build polymer clay directly on top of the plaster mold, and you can cook it on a baking sheet without removing it from the plaster. If you cover the positive mold with plastic wrap, you can build papier-mache on top of it.

• When you finish using the plaster, do not rinse it out in the sink. Plaster will set even if the water is running over it. If you pour it into your sink, it will set in the pipes and ruin your plumbing. Allow the plaster to dry in the bucket, then beat the sides of the bucket with your hands. The plaster will break apart in the bucket, so it can be dumped in the trash can. Wash your hands under the spigot outside. If you wear rubber gloves while you are working, you do not have to wash plaster off your hands when you are done. You can allow the plaster to dry on the gloves, and break it off in the trash can after it is dry. Make sure you cover the surface that you are working on with newspaper because plaster is hard to clean from some surfaces.

References

• Fuse News: Making Your Own Molds Part 1
• Ceramic Arts Daily: Forget the Plaster! How to Make a Surprisingly Durable Hump Mold out of Unfired Clay