Alginate & Life Casting

This page is about Alginate, check out the main project index for the rest.

Alginate is used for life casting directly from skin because it is ‘skin safe’ – this is what the dentist uses to make a cast of your mouth if you need a crown fitted etc. Alginate is made of seaweed, so it is a natural product, supplied as a powder it is mixed with water to set. This article shows some sample products and projects.

Alginate is typically used for life casting, which means taking a mould directly from a person’s skin. It is important that you use something skin safe for this, and also something that will peel off easily. You can get hold of Skin Safe Silicones, but theese tend to be expensive. Alginate is a ‘one shot’ moulding compound because the mould is typically destroyed during the process. Alginate is mixed with water and sets in around 4 minutes. Once the mould dries out then it will shrink and crack, so it must be used to make the cast immediately after the mould is taken.

Pictured above is a 550g packet of Alginate mixed up with water in a bowl. The alginate has been spread onto my hand, and once set it is removed. Then a plaster cast is taken from the mould, and the Alginate is broken away to reveal the cast. As you can see this gives a very detailed cast. As Alginate moulds get larger, they will need supporting with Modroc, so that you can cast wet plaster into them without deformation.

Here’s a video about life casting with Alginate, and also producing a clay press in the Alginate mould so that a plaster mould can be taken for latex casting:

Alginate is available in fast and slow set varieties – although fast is about 1 minute and slow is about 4, so watch out for the fast version.

Alginate is also available is a Chromatic variety which changes colour as it sets, so you know when it’s mixed, ready for application, and set.

If you are considering a large Alginate mould of more than around 1.5Kg of Alginate, then you need to be very careful – Alginate is very wet, so it gets heavy, and the plaster you cast into it will also be very heavy. You’ll need substantial support from a Modroc mother mould to back up the Alginate and you’ll have to consider how you stop plaster flowing out of any holes in the mould that are caused by, for instance, the person’s limb where it’s attached to their body.

Alginate doesn’t stick to itself once it’s set, so you have to apply it all in one go, which can also be problematic for large casts. Never encase any part of a person in plaster directly because it gets hot as it sets and can burn – always use a skin safe moulding compound such as Alginate.