How to Make a Plaster Mold of a Hand
Alginate will make a positive plaster mold with fine detail. The process (or something very similar to it) is also used by dentists to make casts of the human mouth for dental appliances. When working with alginate, you have to work quickly. If a mistake is made, the alginate is cheap enough that you can do the process over again if it does not work out.
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Things You'll Need
- 1-pound alginate bag (dental supply catalog)
- Clean container (1-inch wider than hand on all sides)
- Clock (with second hand)
- Whisk
- Plastic tub (holding 2 quarts)
- Plaster (1-pound bag)
- Knife
- Needle
Instructions
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1
Mix the alginate in a clean container. Estimate how many scoops of alginate you will need in order to fill the container half full, but do not put the alginate into the container. Add the proper amount of water to the clean container. According to the instructions for HydroGel brand alginate, four scoops are a 1/4 pound, which requires 2/5-cup of water. Make sure that the water that you add is in accordance to the instructions that come with your alginate.
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Keep an eye on the clock since the alginate sets very quickly. You have 45 seconds to mix up the alginate. Scoop out the alginate into the water and mix it so that there are no lumps. Use a whisk so that you can mix the powder quickly. Tap the container to help get out any bubbles that don't belong in there.
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3
Tap the sides of the container to get out any bubbles before inserting your hand. Insert the hand into the mixture in the position that you would like to have it in. Hold your hand in the container perfectly stationary for two minutes. The alginate should firm up and become rubbery. Check the alginate to see if it has set up all of the way by probing the mixture with your index finger on your other hand where it will not affect the impression you are making. Proceed once it is firm.
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Carefully remove your hand. You may have to blow into the mold so that the vacuum in it does not keep your hand from moving. Place your lips at the junction between your hand and the alginate. Blow air into the crevice to get air between your hand and the alginate (like inflating a rubber glove). Start gently pulling your hand out. Be careful not to let the blowing or the pulling damage the impression. Once your hand is out of the impression, proceed.
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5
Mix the plaster. Get a quart of water and pour it into a plastic tub. Add plaster. Make sure that any lumps are broken up in the plaster before the plaster gets wet. Spread the plaster evenly around the bucket. When the plaster starts to peak above the water and is wet but does not sink, stop adding plaster. Mix the plaster well. Mix the plaster so that it has a runny consistency by adding more water, if desired.
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Pour the plaster for the mold into your impression. Jostle the mixture by slapping your hands on the sides of the container as the plaster goes in to release any bubbles. Beware that this may cause some of the plaster to squirt upwards if you are not careful. If the fingers were curled in the impression, make sure that you turn the mold so that the bubbles can find their way out, but do not spill the plaster. Since the plaster mold is small, there is no need to add fibers for reinforcement.
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7
Allow the plaster to sit and cure for 24 hours before gently cutting away the alginate. First cut away (with a knife) the general outline of the hand and then shave off layers closer to the plaster molding. When you get most of it off the mold, use a needle to remove the small bits that still adhere to the plaster.
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Tips & Warnings
Keep the water you use at room temperature or the alginate will set up much faster.
Keep the powders and mixtures out of reach of children. Wear safety goggles during this entire project. Wear a dust mask when working with the powder. Do this process away from material that the powders would damage/ruin. Wash the plaster off of your hands and use lotion since it will dry your hand.
