Alginate is a flexible mould/impression making material manufactured from kelp(a variety of seaweed). When Alginate powder is mixed with water, a gel is formed which is then used for life-casting (making moulds of the face, body, feet and hands, etc.), as it is completely safe in direct contact with the skin and sets quite rapidly. Also used to reprodue patterns and mouldings in plaster, timber, cement, stone and many other materials.
Alginate has several advantages over other modelling materials -
Sets very quickly and can be separated from the subject within 3 to 4 minutes of application.
Clean, economic, easy to apply and needs no special skill or tools, additives, etc.
No release agents are required against non-porous surfaces as the mould detaches from the original as it sets. Vaseline can be applied to avoid trapping hairs, cloth fibres, etc when doing life casting.
There are two ways of creating an alginate mould - by Immersion and by Spreading onto the object
Immersion - Where the gel is poured into a suitable container and the object is immersed while the gel sets.
Spreading - A thicker mix is used than for the immersion technique and the alginate is spread/brushed on to the object and sets into a rubbery layer which can be peeled away after a few minutes.
The powder to water ratio for immersion moulding is around 35-40:100 by weight and when spreading, a stiffer mix is needed - usually 50-60:100. A 550g packet of alginate makes approximately 1.6 litres of gel when mixed 40:100.