I was asked a question yesterday concerning the selection of the correct material to make a life casting of a baby’s hand and foot. An alginate impression material is a good choice. But even better, is a formula that we developed using only food grade ingredients. In addition it contains no silica or heavy metals as most alginates do. More importantly the formula is a soft-setting, about the hardness of a hardboiled egg allowing an easy extraction of baby’s hand or foot. Traditional formulas (we manufacture them as well) set rather firmly making it more uncomfortable for the baby when being removed from the mold.
My recommendation was our Hollywood Impressions with a set time of about 2-3 minutes. In some cases that set time might feel a bit too long, especially for an uncooperative model. At those times simply mix the impression material and then wait a minute or so before immersing baby's hand or foot into the mold container. In that way the body part is only there for less than a minute until the impression material sets and you can easiily remove the baby’s hand or food.
Make certain you are not using hard water when combining the water with the alginate powder. Hard water will prevent a smooth mix. In some instances, very hard water will prevent the alginate impression material from even setting. You should test the alginate and water mix before your mold making session to prevent disappointment. An even better suggestion is to purchase a container of distilled water in advance of taking the mold. That will assure you of the best possible mix.
Water temperature plays an important role, too, both in the chemistry and in the comfort of you model. Read the directions for set time on the mold powder package. It will provide a set time based on a water temperature. If your water temperature varies from the recommendation, so will your set time. The warmer the water, the faster the set time will be. Therefore, if the manufacturer lists a 3-minute set time at 80 o F water temperature, and you use 90 o F water, the set time will be reduced. We do recommend a 90 o F, water temperature for the comfort of your baby. Thus, another reason to test your mix in advance so you can experience the actual set times yourself, before you carry out mold making on baby.
With those few suggestion you should create an excellent mold.