I'd read a number of articles about body-part casting using a magic substance called Alginate. This stuff comes as a non-toxic dry powder which when mixed with water turns into a fast setting gel. When mixed it smells vaguely citrus-like. It's the stuff that dentists use for doing moulds of your teeth if you've had any of that sort of dental work done.
I hunted around and found two good sources of the stuff in Australia. The first was just up the street from where I live in NSW at Barnes and the second was in Victoria from Dalchem. Both seem to have reasonable prices and both deliver. Due to my deciding to do this over the christmas/new year period when shops were closed and a mixup with the courier I ended up ordering it from both. Not to worry, I have plenty now.
The basic ingredients for the hand casting are:
- A large-enough container to use to hold the moulding compound
- Alginate
- Plaster
- A stirring implement or two
- A body-part
- Vaseline
- Water
- Mixing bowls
- Paper towel to clean up with afterwards

The next step involves preparing the body-part. The advice that I'd read on the net suggested that using petroleum jelly to coat the body-part helps when trying to get the part out of the gel later. This seems to be true, so we'll do that next time too. We used just enough to coat the skin, but not so much that there was any significant residue.

Now is a good time for your body-part model to practice the desired posture for the mould. The Alginate mixes into an opaque gel so your model won't be able to see their body-part once immersed, so a bit of practice in adopting the right posture and then putting it into the mould container helps get it right at show time.
Next you mix the Alginate gel. There was a trick here that wasn't obvious until it came time to actually do it. The trick is determing how much of the Alginate powder and water you need. The stuff is reasonably expensive so you want to minimise waste. At the same time the stuff sets pretty quickly so you don't really get time for a second chance. The trick is to work out how much you need and to mix that amount.
The Alginate I used recommended a ratio of about 4.25 parts water to 1 part Alginate by weight. The trick here is what you're looking for is a target volume and I couldn't find any guidance on how you did that.
I started by looking at the container and figuring out what my target volume would be. A simple experiment involving filling the container to the brim with water and putting Mary's hand into it to see how much water was displaced determined the volume of her hand.

The result was an enormous-looking amount (by volume) of powder. Looking at the two it seemed clear that there was no way those two were going to mix into an amount that wouldn't be more than what I wanted, even after taking into account how much the powder would pack down. So I scaled the amount down and ended up with about 1 litre of water and about 250 grams of Alginate. It still seemed like a lot, but I trusted my instinct.
Here I learnt something; my instinct was wrong. The alginate virtually disappears into the water. Next time I'll just do the calculations assuming the volume of water pretty closely approximates the desired volume of the gel. As I mentioned earlier there isn't really time for second chances so I ploughed on ahead anyway.

Now the fun bit. The body-part model slowly eases their body-part into the goop. It'll be cold and slimy initially. A bit of a wiggle of the body-part helps to ensure that the Alginate gel has made contact all over. They now must keep the part pretty much immobile while the gel sets. I insisted on waiting the full five minutes before testing if the gel had set. They'll know when setting occurs, if they very gently try tiny wiggles they'll feel the gel has solidified around their part. This stuff ends up with a texture/consistency somewhat like Silicon sealant. It's firm and rubbery.
I'd read a fair bit of advice about how to actually remove the body-part from the gel after it has set. The problem to overcome is atmospheric pressure and vacuum. The trick is to get air into and around the skin so that the vacuum doesn't hold it in. I've seen people suggesting blowing air in and this might be a good idea. We opted for a gentle pulling motion combined with gentle wiggles.

Now comes time for the cast itself.


I learned a few valuable lessons here. Firstly, don't rush this bit. I was excited and wanted to see how this would turn out so I didn't stir the plaster properly. I stirred it by hand, next time I think I'll use a paint stirrer and an electric drill. Secondly don't make it too thick. The plaster needs to be fluid enough to reach the extremities of the mould while at the same time allowing air bubbles to escape. Pour the plaster slowly to prevent the air bubbles being there in the first place. I read somewhere that it's a good idea to pour some in and then rotate the mould around in all angles to coat the interior surface of the mould with plaster before pouring any more in. This was good advice and I wish I'd taken it; next time. After you've poured the plaster you can gently agitate/tap the mould to encourage the air bubbles to rise to the surface. I did this and you can see that it works quite well. Keep in mind the shape of the object you're casting though, air bubbles can get trapped in high points inside the cast, the idea is to get them outside.
Now comes the waiting. Put the whole thing aside and leave it alone until you're sure the plaster has set.
Don't touch it. Wait.
Keep waiting.
Are you sure the plaster should have set already?


Argh! A finger is broken! How did that happen? It was a clean but not perfect break so it presumably occurred late in the setting of the plaster. I really don't know how it happened but I'm pretty sure it didn't happen while I was removing the Alginate. I do recall moving the mould at some point during setting because I'd put it in a silly place and maybe it broke then. Next time I'll follow the advice about not moving it.

Now to finish it off.
I used some acrylic paint to paint the hand. I'm no artist and frankly the acrylic paint was annoyingly thick so the paint job isn't fantastic, but I think the end-result is honest.


I've got a few ideas for things I'd like to use various casts for.
Next time I'll get the kids involved too, they'll love it.
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