Casting Help
The Casting
The casting bit is the slightly trickier part as you have to make sure that you eliminate all the air bubbles or else you will have holes in your cast. We use a strong white plaster which is stronger than plaster of Paris (which is too soft), our plaster is strong but still easy to sand down if you need to, to fit into your frame or glue onto a plinth, making it good to work with.
When you mix the casting powder, put the water in the mixing container first and add the powder, let the powder soak up most of the water for a minute or so before you begin mixing it, this will ensure that the water is absorbed more evenly and you will be less likely to get lumps in your mixture. You should mix until you have a thin yogurt-like consistency but mix slowly and not too much, as you do not want to add too much air, as air bubbles are your enemy in life-casting! As a rough guide you will need twice as much plaster as water but plaster is generally quite forgiving and will set anyhow, the strength of your casts will be affected though if you do not use enough. Remember that your plaster once opened needs to be stored in an air-tight container and in a dry place and if any is not used after approx. 6 months then when you mix it, it will set more quickly as it deteriorates, do not use if it is more than 12 months old.
Once mixed, pour some of the mixture into your mould, swish it around and pour it back out, this is to ensure that you reach all the ends of the toes or fingers, some people like to paint some mixture into the ends with a paintbrush to ensure that all the ends of the fingers or toes are reached and have no air bubbles in them. If it is not possible to reach the ends of the fingers or toes then you will need to tap the half filled mould on a hard surface, several times to make any air bubbles rise to the surface, you may even wish to hold a damp cloth (j-cloth will be ideal), over the end and shake and turn the mould to ensure that the mixture has gone right into the ends, when satisfied that you have got the mixture into every part (take the time to do this part right), remove the cloth, finish with more tapping on a hard surface and re-fill the mould to the top and leave to set.
When set, peel away the alginate carefully in very small pieces so that you don’t break off any fingers or toes and leave your cast to dry out thoroughly. If you do break off a finger or toe then you may still be able to salvage your cast by gluing it back on, let the pieces dry out, then glue, you can also wipe over the join with a little new plaster and a wet finger, a little paint then you can hide the join quite well.
Let your cast dry out for at least 3-4 hours in a warm place, longer if it is a larger cast, leave to dry out thoroughly. When it is dry, it will be quite strong and you can sand the base to flatten it if you are gluing it onto a display plinth or a small area at the back of the cast so that you can get a good surface to glue it into the frame.
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