For people interested in life casting – using molding and casting to create replicas of human bodies – the process starts with the right materials. The common choice for molding material is alginate, for its health and environmental safety as well as its ideal setting properties. Though the base is the same, alginate products can vary in the specific mixture and how it sets. To know how to pick your alginate and where to buy it, here is some information to start you off.
How Alginate Is Made and Used
Also called alginic acid, alginate is derived from processing dried brown kelp. The kelp is dissolved and combined with other raw materials into an aqueous solution, then dehydrated to form sodium alginate powder. This powder may then be mixed with water and other components in varying ratios or sold directly in the powder form. Mixed with water, alginate molding powder forms a thick gel, with viscosity depending on the powder-to-water ratio. When left to set, the gel becomes a flexible, rubbery solid as the polymers link together.
There are two main processes for creating a mold with this gel. Small objects or body parts can be immersed in a small container filled with the gel, held in place to allow a surface to form around the object as the gel sets; after a few minutes, the model is carefully removed, leaving the solid mold. For larger objects or body areas, including the face or torso, a somewhat thicker alginate paste is scooped and spread over the surface area, with possible reinforcement after it sets.
Alginate, though it comes from the same base, is not a “one size fits all” product; the specific formula used in the powder or solution can alter the final mold – how quickly it sets, how stable it is, safety for the model involved, and so on. When looking for where to buy alginate, seek out a retailer that specializes in what kind of project you’re planning.
If you did a search for alginate powder online, you’d likely find mostly results about dental impressions. While this is one application of alginates, it requires a slightly different formula from life casting or other craft purposes. Craft supplies stores and retailers often carry alginate molding powder or solution, but retailers that deal primarily or exclusively in life casting supplies will more easily yield the product you want.
Finding the Right Alginate
Alginate formulas vary mainly in setting time, water temperature, and additives and fillers such as clay or silica, and these factors affect the ideal use of each formula.Generally speaking, a larger casting will need a firmer set. This means a longer set time, as well as fillers and a larger powder-to-water ratio to thicken the resulting mixture. This alginate will resist dripping and form a sturdier mold that can be easily removed from the model. On the other hand, a softer set – with fewer or no additives and a more economic ratio of alginate molding powder to water – is preferable for immersion molding or for the safety of children and infants when making life casts of them.