Alginate casting
What is alginate?
Alginate is a powdered molding material. It is a combination of chemicals and alginic acid which is derived from seaweed.
Mix the alginate powder is mixed with water. As it begins to set up, the alginate mix becomes a flexible, rubbery mass where lifecaster waits for it to set. The fine grained nature of the alginate ensures that the alginate has flowed down closely against the skin so very fine details are captured in the mold. These details are then transferred to the casting.
How to mix alginate
If you're just mixing enough for a face cast (3-4 ounces), mixing in a small container with a paint stir stick or spatula works well.
Amounts larger than 4 ounces and up to about a pound, a kitchen whisk and a large bowl is a good method. You can also use a sturdy plastic bag to mix in. Put in the alginate powder, put in the water, push out all the extra air, grab the bag opening firmly, and mash and knead the bag for about 2 minutes until the alginate is well mixed.
For larger amounts, a power drill with a "jiffy mixer" attachment on it works well. A jiffy mixer or a paint mixing attachment for a power drill can be purchased at most home improvement or paint storest.
Depending on the set up time of the alginate you are using, fast and efficient mixing helps for a successful process.
How much alginate is needed?
A face cast requires about 4 ounces of alginate.
A torso cast (shoulders to belly) requires between 1 1/2 and 2 pounds of alginate.
The requirements for a hand cast vary with the size of the molding conatainer and whether it is a single hand or multiples. The conatiner should be large enough to fit the hand or hand(s) comfortably without touching the sides or bottom and deep enough to capture enough of the hand/wrist.
Fill your container with water an place it in a sink or place you can overflow water. Have your model(s) put their hand(s) into the conatainer and let the extra water overflow. Measure how much water is left in the bucket.
A pint of water weighs 1 pound, a quart- 2 pounds, and a gallon weighs 8 pounds. Check the instructions with your alginate to get the corrrect mixing ration. For example, a 4:1 ration would use 1/2 gallon (4 pounds of water) to 1 pound of alginate. This is ratio by weight, not by volume.
Casting the piece
Hydrocal or Hydrostone arethe most common casting material for alginate molds. Plaster of Paris is considered too soft for casting. There are many options depending on the desired final output of the casting.
Is alginate toxic?
Lifecasting alginates are non-toxic and biodegradable. It is suggested that the model be tested for allergies as this can occur in rare cases.