What is Alginate?

Depending on the level of detail required and the complexity of the form to be moulded there are a number of different ways to cast any part of the human anatomy. The most frequent requests are for hands and faces to be cast with as much detail captured as possible. Alginate is ideal for this as it is a liquid gel that can flow over and into the finest of detail.

The most common mould-making methods for making life casts are skin and jacket mould making or encapsulation or single part open mould making.

Tiranti’s medium set alginate powder.      
                    Just add water
Plaster casting of a bottle held into alginate

Alginate colour ranges from white to yellowish brown and pink or green, the one we use however is a blue powder. Alginates are primarily used by dentists to take a cast of the inside of a patients mouth, although it is used a lot through-out the visual/special effects industries for casting detailed body parts and particularly to copy an actor’s or actress’s face, hands and feet, because there is so much detail to capture.

Commercial varieties of alginate are extracted from seaweed so are completely safe to use on skin and inside the mouth, it has pleasant biscuit-like aroma to it but it is not recommended to shallow any, however hungry you may be!

The are 3 types of alginate slow set, which sets in 8-10 minutes, normal set which sets in around 3-5 minutes and fast set which is too quick setting to use for most life casting situations at around 1-2 minutes.

Group casting of twelve 3 year old’s, made using a clay walled vessel on a table
Two year old’s hand casting
 Distorted torso cast
          Stage 2
          Stage 3
          Stage 5
Polished aluminium life cast
 Casting revealed and sculpted
Tiranti’s medium
 Torso pose plaster cast
       Revealing the casting
Two part alginate/modroc mould removal to reveal cast

How do I use Alginate?

To capture any significant amount of detail Alginate must be used. It is supplied in a waterproof sealed bag or tub which contains the very fine alginate powder, this is mixed with cool water, quickly and with an electric whisk ensuring all lumps of powder have been mixed in properly, once the liquid is a smooth texture it can be either poured into a prepared vessel or pasted onto a face.

To make a face casting the process is described below for

  1. 1.The model or subject will need to be briefed on the process and will need release agents applied where appropriate. Applying any material carelessly to the face can be dangerous. Alginate is applied in a particular fashion and inexperienced users should NOT attempt this without supervision.

2. Once an even layer has been applied, creating a skin of alginate on the face, it will want to slide off again so for 2-3 minutes it can be fun trying to keep it in place while it sets. Making the mix thicker will help it to stay in place when moulding a vertical surface.

Tip: adding more water will make the alginate go further, but will also take longer to set, just as adding more powder thickens the gel but speeds the curing time.

Cold water will retard the cure while hot water will accelerate it.

  1. 3.After it is set completely (4-5mins) it is necessary to reinforce the alginate with a plaster bandage jacket. Much like the way hospitals set a broken limb with strips of plaster impregnated bandage. Its common name is ‘Mod-Roc’. This in turn takes around ten minutes to set completely.

4. Once cured the whole thing is removed as one. Taking care not to tear the alginate skin, which is very fragile.

  1. 5.Once the mould is away from the face the nostril holes can be blocked using more mod-roc, when this has set the inside (of the nostril holes) must be coated in release agent to prevent the casting getting stuck in the mould. (Alginate doesn’t stick to itself but plaster will.)

  1. 6.This done, plaster can now be prepared and poured into the mould straight 

   away. Usually alginate will only last for one cast because it has a tendency 

   to tear very easily but 2-3 can be cast if the mould shape is simple enough

   and the user is very careful!

Alginate, mod-roc, and plaster are available from:

Alec Tiranti sculpting supplies

Prices vary:

£8.00 for 500g of alginate

£10.00 for 25kg and plaster

£2.00 per roll of mod-roc