Cast Your Own Hand

I get requests, from time to time, about instructions on how to do castings. Do check out the other pages I've put together on this. Also consider getting a local starving artist to do some of the work for you. (hint, hint).

With that out of the way, here's how to do the simplest life casting you can do: hands. Hands are really neat, because:

They have lots of interesting texture
They're not terribly private; not too many folks mind baring their hands
They're intensely personal. I can easily recongize my own hand.
They're flexible. You can cast a fair ways up the wrist and still be able to pull a hand out of a mold. This means you can cast the whole thing without having to make multiple-piece molds.
They're small. You don't have to spend a fortune to cover acres of skin.
They're at the end of your body. You can stick them into a bucket, pull them out, and be done, rather than having to work out how to get the mold off of a body. Also, when you're pouring plaster, the shape left by the hand is easy; just pour plaster in and be done. No spending time working plaster by hand up the sides of a big shape.

Stuff:

What	Why
Electric drill	You need something stronger and more enduring than your arm to mix the alginate, probably. Not a must, but definitely a help. Skip this if you prefer to whip eggs to a stiff peak by hand rather than using a mixer. DO NOT bother with a cordless drill. They're engineered for torque, not speed. Use the plain old fashioned plug-into-the-wall kind.
Paint mixer	This is a metal doodad that you put into the drill to help mix. If you're not going to go spend the $15 this will cost, skip the drill, too.
Cheap pitchers. At least two.	I use Sterilite 2-quart (2-litre) pitchers, about $1.50 U.S. They're nice and sturdy, plus tall and narrow. Also, they're cheap enough to not cry about if you forget and let plaster set up in them. If you're really cheap or on a budget, 3-litre soda bottles also work, but not for large hands.
Newspaper	Or other disposable surface. Plastic tarps are great for big stuff, but are overkill for just hands. Also, you'll want something small to hold in splatters from the pitcher you're mixing plaster in.
Alginate	Buy this from Pink House Studios. I can't recommend anybody else; I've only ever tried one other brand of alginate (from Douglas & Sturgess), which I didn't find to be as good as Pink House. One small hand takes about 6oz.
Plaster	I use TufStone, which is well suited to solid casting. Use any plaster you like, but be aware that you get what you pay for.
Water	Tap water is fine for use with plaster and alginate. On the other hand, I have water I don't mind drinking straight from the tap. If you don't, consider using bottled.
Wooden dowel	Or something similar. You'll stick this into the cast as it is setting. Later, this will give you a handle to hold while you break away the mold material, and to hold it while it dries. After it dries, you can cut off the dowel flush with the base, and put a screw into the dowel to hold your casting in place. You'll want about 1 cm or half an inch or so in diameter, and 10cm long (5-6 inches).
Scale	A diet scale is good enough; a gram scale is probably overkill, and your bathroom scale is pointless. If you bought enough alginate to experiment with, but not much more, you may not even need the scale. It is worth emphasizing, though, that you are going to have more trouble if you treat this like cooking, and try to measure the alginate by volume. The reason lots of recipes call for sifting flour is to regularize how much flour you get. If you really smash it into your measure, you can double it versus sifted.

Steps:

What	How
and, Vogue!	Decide what pose you want. Holding something is fine, mostly. If whatever you're holding will also be held by the alginate when it sets, fine. If it's entirely, or almost entirely covered by your hand, it's just going to drop loose into the mold when you take your hand out. If the thing you're holding isn't smooth, or loosely held, you won't be able to slide it out of the hardened plaster. Think about whether that's OK. One thing you want to be aware of is the shape of your hand. If you curl your fingers under, that will leave a shape in the mold that plaster won't sink in to. If you pour the plaster straight down, it'll fill level with where your fingers bend back up, and stop. The air trapped where your fingers were will stop the plaster from rising into them. If you want a pose like this, it's very important to remember how you held your hand when you're pouring plaster. If you take that same shape, but turn it sideways, and pour the plaster in at a very gentle angle, there isn't any space above to trap air.
Fitting rooms...	Once you know what pose you want, see if it'll fit in the pitcher you have. You need to be able to hold the pose without touching the sides of the pitcher, bucket, or what have you. You don't need much of a gap; 1/4 inch or 1/2 cm is fine. The closer the fit you get to the bucket the better, because that means less alginate to mix.
Pick a place	You want a place with running water, floors you don't desperately care about, and somewhere you can make a mess for an hour or two. Outside is fine. Even freshly-set plaster can be blasted off with a garden hose.
Protect your working area	Put down newspaper where you'll be mixing and measuring. Put some more down around the sink. Save a section to use to cover your pitcher while you're mixing.
Guesstimate the volume you'll need	Once you know your pose, pour water into your bucket or pitcher, and stick your hand in. Slosh water out until it's at the level you want your finished casting to come to. Now pour out about a fifth of the water. Whatever's left is how much water you need to use to mix the alginate.
Measure the Water	See how much water you have from the prevous step. If you're in the U.S., please devote 60 seconds of silence to the desperate state of measurement and science education here. Done? OK. Figure out how many liquid ounces of water you have. Oh, sorry. Figure out the number of cups of water you have, and multiply by 8 to get (fluid) ounces. Fortunately, for water, fluid ounces are (roughly) the same as weight ounces. Divide that by 6 to get the number of ounces of alginate you need to mix with your water. If you're practically anywhere else, measure how many cubic centimetres (cc's) of water you have, and thus how many grams. Divide by 6 to get the number of grams of alginate you need. Note: Six parts of water to one of alginate (by mass) is pretty arbitrary. For Pink House alginate, it makes a mix about as thick as stirred yogurt, maybe a bit thinner. This flows well around hands and into tight places, is economical, and is just durable enough to stand up to pulling a hand out. Fiddle with your ratio a bit, but six water to one alginate is a good place to start. Alginate will "gel" at much higher ratios (16:1), but takes longer to set, is comparatively weak, and slumps under its own weight.
Weigh alginate	If you've skipped the part where you got hold of a scale, you're going to have to eyeball it. Start with one quart of water and one and one quarter cups of alginate (well fluffed). If you have a scale, weigh out as much alginate as the previous step says you need.
Mixing	Put the water in your selected container first. Put the drill in, and get the water moving a bit. Add the alginate. If you've got a drill, it doesn't much matter if you add it all at once or a bit at a time.
Keep Mixing Done Mixing	This mix is thin enough that you're going need to mix for about 90 seconds before it's really smooth. Thicker mixes go much more quickly; they're too thick to easily get out of the way of the mixer blades. Thin is what you want for minimizing bubbles and getting good detail, though. The pictures are of a mix that still has small lumps, and one that has been mixed until it is smooth. When you're done mixing, take a minute to clean off your mixer. For some reason, alginate sticks really tenaciously to stainless steel (or perhaps, metal in general). Cleaning it now, when it's soft, and running water can help break it loose is much easier.
Vacuum	I have the luxury of a couple of vacuum pumps. I use these to de-bubble the mixed alginate prior to putting hands in. The alginate will swell to 2-3 times its original volume before the bubbles break. In the picture at left, it's well past time to start shaking the vacuum chamber to help the bubbles rise out.
Put the hand in	Get your hand damp before putting it in. Not running with water; get it nice and wet, then do a bad job of toweling it off. The point is to get water, which does a really good job of wetting skin into all the tiny cracks and crevices, but not so much you thin out the alginate. Put your hand in very slowly. The point here is to let the alginate run up against your skin so slowly that it can keep air out as your hand sinks in. Once your hand is well under the surface, do your best to work it around in the alginate to knock off air bubbles. Mash it against the sides, work your fingers around, and use your thumb to reach the web between your fingers. When you're done with that, strike your pose. It's surprisingly hard to feel what your hand is doing when it's in the alginate. You may find it helpful to put your other hand next to, but outside of, the pitcher and mimic the pose you want. When both hands are doing the same thing, and you can see one hand to correct it, it's easier. You will find your hand drifting around in the algiante. When you feel yourself bumping a side, just move your hand very gently away until you can't feel the side. As the alginate starts to set, you'll get this feeling from the alginate itself. It's important to not tear the alginate when it's this tender, so be very gentle when moving. If you find you can't move your hand gently, the alignate has set. Just stop, and hold still. It takes 15-20 minutes for the alginate to set, and then get strong enough to withstand you pulling your hand out. Wait patiently, read a book, klonk your sibling over the head with the whole pitcher-hand assembly, whatever. Just wait. When you can poke the top of the alginate with your other hand and it feels pretty firm, you can start wiggling your wrist. You will feel the alginate start to pull away from your skin. Take your time. Work a little bit of your hand at a time. Concentrate on feeling your hand come free, and feeling an air gap next to your skin. Keep wiggling until your entire hand is completely freed from the alginate within the mold. Only then, move very slowly to pull your hand out. You'll get a nifty sucking sound as your hand almost seals up the wrist opening, then a whoosh as your hand comes out.
Inspect your mold	Scope out the inside of your mold. There are a few flaws in the sample at the left. I intentionally didn't wet my hand or brush off air bubbles, and you can see the effect. Look at the base of the fingers where they meet the back of the hand.. You can see that there are bubbles between all of the fingers. Also, there's a bit of tearing between the last three fingers. This is pretty normal, and won't affect the look of the casting much at all. Let your casting drain upside-down overnight, or for 24 hours. The alignate continues to set and shrink during this time, which squeezes out water. If you cast immediately, this water will get squeezed out into the plaster mix, thinning it locally. Also, because water is about half as dense as mixed plaster, it will run up the sides of the casting as it is setting.
Pour Slowly SAFE_POUR TRAPPED_AIR	Mix up the plaster just as the package directions indicate. The plaster manufacturer has been in business for a lot longer than I have, and they know what they're doing. Again, if you have a vacuum pump, you can save yourself some trouble here. If you posed your hand so that it might trap air, look carefully into the mold before pouring in the plaster. If you put the mold at a shallow enough angle, you can almost always work around any odd shape. See the two very crude diagrams at the left. In the bottom one, the model has curved his fingers back. If you just pour straight in, plaster won't go out to the fingertips. If you put the same mold on its side, and turned 90 degrees, you can pour plaster without trapping air. Shake any excess water out of the mold before pouring the plaster. You've got about 10 minutes before the plaster starts to set, so go slowly and carefully. Also, if your pitcher is new, be careful that you don't shake the alginate mold completely out of the pitcher! Pour the plaster very slowly into the mold. Pour it so that it hits the top edge and runs down the side. If you pour it straight in, you're guaranteed to be mixing in air bubbles. Now, pour it back out. What's the point? The point is to use the plaster to dilute any water you might have still left in the mold. Also, any bubbles in your plaster have very bad surface tension. Pouring most of the plaster back out leaves a thin skin of plaster with bubbles sticking out. These are pretty easily popped just by blowing on them. Again, pour the plaster back in very slowly. Now, jiggle the daylights out of it. Bang it and shake it so it rattles on the tabletop. You're helping air rise out of the thickening plaster. Once the plaster looks like it's getting thick, stop.
Insert dowel	Before the plaster gets too hard, stick in the dowel. You should make the dowel not-straight somehow. Make some cuts into the side, or glue another piece of dowel to it. The water from the plaster will swell the dowel, and when everything gets dry again, it will shrink and become loose. For using the dowel as a handle to manage the casting when it's just finished, it's safe, but if you were going to put a screw into the dowel to fasten your casting, you need to rough up the dowel or it won't stay put.
Remove the mold	Wait a few hours for the plaster to set up. I usually wait overnight, but I'm not sure if that's really necessary. Grasp the dowel and pull. Hopefully, your alginate mold and the plaster will all come with it. It didn't, right? No, it doesn't for me, either, unless I have a really new pitcher to work with that isn't all scratched up on the inside from the mixer. Okay, get a loooong thin knife and work around the sides. Once you've got the whole thing out, use the dowel to hold onto it. I've drilled holes in a chunk of wood for the purpose.
Break the mold	Now that it's out, grab the mold, and pull it apart. It's initially pretty stiff, but once you've got a crack started, it tears away pretty easily. DO NOT TOUCH THE CASTING while you're removing the mold. Wet plaster is very very soft, and you can easily spend two seconds creating twenty minutes of fix-up work. Use the dowel to hang onto the casting.
Picking	Of course, not all of the alginate will tear cleanly away. Use a toothpick or a wooden skewer to clean up the smaller pieces. If you can see wet, loose plaster on the surface of your mold, fill a sink or big bowl with cold water, and gently swoosh the casting around in it. DO NOT use running water. Even that can eat away at detail in fresh plaster.
Thumbprint detail	With a bit of care and practice, you can get castings that reproduce detail much finer than a fingerprint.
Runnel	If you pour your plaster too soon, or you are not careful to pour it into and then back out of the casting, you'll get these: runnels. This is caused by water seeping out of the mold and into the plaster. Since the water is less dense than the plaster mix, it tends to run up along the side of the mold making these tracks. These are an enormous pain to fix up.
Bubbles	If you don't get your hand wet before putting it in the alginate, or you don't work to get trapped air bubbles loose once it's in the alginate, you'll get bubbles. These are from air trapped on hair on the back of my hand. You can see where I've started to smooth them out, but have lost all of the skin texture. This is usually more trouble than it's worth. If this were for a project of my own, I'd scrap it and start over. If this were a comission, I'd be looking at most of a day of work to try to badly reproduce the seams and lines and merge them with the real versions.
Holding tapes	I also used this demo as an experiment. I put a spring inside some plastic tubing, and plugged the tubing up with cotton from Q-tips. I then taped the whole thing to a bamboo skewer. After I'd poured the plaster, I used the skewer to hold the spring in place until the plaster was thickening.
Spring closeup	After the plaster was dry, I used a very fine saw to cut through the plaster around the spring. Plaster is very brittle, and also pretty soft, so the spring wasn't in too much danger of getting damaged. It looks a little silly holding this much stuff, but I'm planning on hanging it up as a hat-clip, a la the Addams Family.