Measurement

Measuring dry powders: Do I really need a scale?

Depends. If you're just going to do a hand or a foot or two, no. Go buy a kit, which gives you everything you need in one box. No leftovers, not much mess, premeasured.

If you're going to go anywhere beyond one or two souveniers from a rainy afternoon, yes. Go spend the bucks on a balance that's good to within a gram (maybe 10g, if you're on a budget) If you're really tight for funds, maybe a diet scale. Frankly, though, if you go that route, you should check to see how accurate the scale is, and how accurate you are when using it.
Check the accuracy by massing out 10 samples of 10 grams each, and then see if the scale says that all 10 poured together are anything like 100g. Do the same thing again, but this time make the sum of the parts the maximum the scale is capable of. This will give you an idea of how much you can trust the scale at low, middle, and high ends.

If you can afford to spend $110-130 or so, break down and get a proper balance. If you're into this, you probably have or will have other hobbies where it's a good idea. Save yourself some repetitive simple math, and get one with a tare (allows you to zero the balance with a cup on the scale, so the numbers on the balance show only the content of the cup)

The whole reason that you want a balance is not for the sake of precision; you can be extremely accurate with volumetric measurement given proper tools. The problem is that both plaster, and especially alginate are loose powder, like baking flour. If you really work to fluff it up as much as humanly possible, you can get reasonably consistent results measuring powder by volume. On the other hand, you waste a lot of time fluffing powder and breathing in the dust.

Measuring liquid volume: Measuring cups?

No. You can get good results with good quality measuring cups, but the number of divisions is generally too few to be helpful, and graduated cylinders are cheap enough to be similar in price to measuring cups. Factor in hassles with getting them clean enough to eat off of after every casting session, and you realize it's easier to just get another set.

American Science & Surplus has various graduated cylinders for sale at extremely reasonable prices. They have a lot of other cool stuff too, but the site is pretty much unusable, because they get too cute with the names of things, so it's hard to search. Call for a catalog.

Vacuum

Do I really need a vacuum pump?

Depends. If you're doing only a few projects, or if you have more patience than I do, you can get away without one.

If you don't get a good pump, you'll spend more time picking blebs off, and packing tiny bubbles. You'll have less fun, spend more time at it, and never really get professional quality results.

Where can I find out about amateur vacuum resources?

The Bell Jar

How good a pump do I need, then?

You need one with an ultimate pressure (the pressure theoretically possible if the pump runs forever on a perfectly sealed chamber) that's good enough to boil water at the temperature you're mixing your plaster or alignate. These are:

Degrees Celsius	mm of mercury
10	09.209
12	10.518
14	11.987
16	13.634
18	15.477
20	17.535
22	19.827
24	22.377
26	25.209
28	28.349
30	31.824

When you forget, a reasonable rule of thumb for temperatures around room temperature, one millimeter per degree Celsius.

1 atmosphere = 760mm; which is to say, you need to remove essentially all of the pressure.

Whats this CFM number for vacuum pumps?

This is the cubic feet per minute of air that the vacuum pump would move if the input and output of the pump were unrestricted. Apparently, this is the best they can do in terms of specifying how fast the pump can bring down an arbitrary volume. Probably there's some easy way of figuring what pump is right for what volume, but I never found it. Best I can suggest is going rummaging on the web.

In my case, I lucked out. I found a new salesman at a local company that reconditions pumps that was willing to take the time to help out a guy who probably wouldn't be a repeat customer. If you're in the San Francisco Bay area, you owe it to yourself to check out Duniway Stockroom Corporation. The guy who helped me out was named Kevin. I have no idea if he will be happy to see repeat business, but it's worth a shot.

They sold me a pump on a sort of a rental deal: I got to try it out for a few days, and if I didn't like it, I could bring it back for a 90% refund. They hadn't fully reconditioned it yet, so they weren't really taking much of a risk (they do a fair business in reconditioning equipment).

As it turns out, a .9 cfm Welch 1205 (no longer in production) will pump down a 7 liter enclosure in under a minute with a good seal. Since my vacuum chamber is homebrew, I use the other crummy vacuum pump, which has a much higher CFM rating (but a much lower ultimate vacuum) to help. The extra vacuum deforms the seal enough to make a good seal, and then the better pump can finish the job.

Good God! Vacuum pumps are expensive!

Yes. Reduction in pressure beyond a certain point requires exponentially better machining, and exponentially more money.

How can I save on them?

Buy reconditioned used pumps. Make absolutely certain your pump does not have phenolic vanes, as these will absorb water vapor and seize, meaning you'll spend nearly as much getting the pump fixed as you spent in the first place. The place I got mine, Duniway Stockroom Corporation sold me a pump even before they reconditioned it; it was still pumping down quite well when they got it surplus. Check out The Bell Jar for a serious amateur scientist's resource for all things high-vacuum.

Supplies

Containers

Trash Can

Get a good, sturdy, waterproof trash can. An old 5-gallon industrial bucket is ideal; I use a sturdy one pilfered from work. Sturdy, because the waste is heavy. Waterproof because the alginate continues to seep water for quite a while (days) after it has set up.

Mixing vessels

Depends on what you're doing. I found some nice 2 liter translucent white plastic pitchers that are fairly tall and narrow. Translucent is good, because you get to see your mixer actually getting into all the corners at the bottom when mixing plaster.

You'll probably want at least three: one to mix alginate, one to mix plaster, and one to hold rinse water for your mixer.

Get these a bit more than twice as big as the final volume of plaster or alginate you want. During the degassing under vacuum, the liquid will foam, and about double in volume. Yes, this is with vigorous shaking.

Massing cups

I find that disposable plastic cups (the good sturdy 12oz ones (Solo brand)) are perfect; they hold 600g of plaster, which is about all my balance will do.

Protecting your Model

Garments

A good swim cap and a barber's cape.

Mold release

Hair conditioner to help alginate release from any stray hair escaping from the swim cap.
Skin lotion with a bit of oil in it
Cholestorol-based hair conditioner for eyebrows, etc. I've tried Vaseline for this, and it makes for substantially worse bubbles in the alginate than conditioner. If you don't completely saturate hair with some kind of goo, the alginate will just run in among the hair, and when you pull it off, either it'll look as if there's no hair there, or little pieces of alginate will rip out, or you'll get trapped air bubbles in the hair showing up in the alginate mold.
Drinking straws. I like McDonald's, as they're a bit bigger than usual, plus they come wrapped for that pseudo-sanitary feeling.
Safe Toy. A dog squeak-toy costs about 99 cents, and lets your model communicate at least a little while they can't talk. If they let go for any reason then you stop everything, clear the airway and then the eyes.

Materials

How much material do I need to cast a hand?

I've only worked with Pink House alginate so far, and I have settled on a ratio of 1 part alginate to 6 parts water by mass. In my mixing jugs, 1.5 liters plus 1 hand past the wrist makes a pretty full jug. So, for 1.5 liters, 250g of alginate, at about $5.00.

The same hand, not terribly surpisingly, needs a bit less than 0.5 liter of casting plaster. I've only used TufStone(tm) so far, and at a density of 2.0, it takes 100 parts plaster to 32 parts water. Roughly 3.5 pounds of plaster costs a bit under $2.00

And for a face?

A bit less, perhaps surprisihgly. I mix up 1 liter of alginate, again at 6:1, and 400ml of plaster is just enough to make a slush cast. 450ml is a bit more forgiving, and 500ml is enough to make sawing off the rough edges tiresome.

Tools

What sort of a vacuum chamber do I need?

Decide what kind of casting you're going to be doing. I decided early on that full-body casting was more ambitious than I had room for in my house. In my own particular case, having splashed out on a proper pump, I decided I could get away with homebrewing a vacuum chamber.

Beyond the one I made for myself, I have no real experience with them, so I don't have any suggestions.

What do I use to mix alginate and plaster?

A paint mixer. It's a stainless steel round doodad on a long shaft that you put in an electric drill. (The trade name is Jiffy mixer, and apparently, that's a common enough name that it's useful to use when asking) Yes, Virginia, get a drill with a cord. I've used a contractor's cordless, and it's just not fast enough to suit me. Your mileage may vary, but you're going to be mixing for minutes at a time, not just driving a few screws.

Do not screw around on this. Get the mixer. It mixes alginate to an absolutely smooth consistency. By hand, I have never even come close to getting all the teeny little un-wetted, bubble-forming, clusters broken up.

It also does a miraculous job on plaster. I just finished an inadvertent series of experiments, and hardness in the finished plaster is very very positively affected by mixing the h@ll out of the plaster slurry.

Random tools I have and like

I've worked at a bunch of jobs, so I have a pile of unused business cards. They are quite handy as disposable scoops for weighing out alginate and for scraping out nearly-set plaster from jugs.
Dental tools in a variety of shapes. I got mine used from American Science & Surplus, but I'm going to ask my dentist next time I go in if there are any dead ones I can have.
Popsicle sticks. Available in a bag of approximately a zillion in craft stores. Useful for mixing test batches, scraping, mooshing and applying plaster and alginate. Also useful for dislodging plaster residue from your nice plastic sink without scraping it up as a metal tool would. Hint, hint.
Stainless large scissors to cut the wet plaster bandage.
Fine-pointed tweezers for packing cotton into peoples' noses without actually putting my finger in.
A small flea comb; very useful for getting alginate out of the fine hair at the nape of your models' necks.

Hardware

What kind of tubing and valves?

Somewhat surprisingly, $5 valves from the local hardware store work perfectly well. You must seal the threaded joints. I used Teflon tape rather liberally, and didn't experiment to see what else would work.

Be warned that $12 will buy you a vacuum gauge which can be relied upon to tell you whether you have excellent, good, fair, poor, or no vacuum. Don't rely on the numbers on the face. At all. Do try to buy one that actually starts from zero.

Tubing can be bought from the same place you get your vacuum pump at a really outlandish cost, or you can just go to the auto parts store and get thick-walled rubber tubing. I imagine if you're also going to do high-vacuum work, you probably care about the volatiles in the rubber outgassing. On the other hand, with the amount of water vapor you're going to be sucking into your pump oil, you might want to reconsider what your ultimate vacuum will be...

What kind of bell jar?

Damfino. I homebrewed mine. Real ones cost about $70 to start, and go up from there. Mine is bigger, more robust, and better suited to the shape of the Tupperware pitchers I use. Check out The Bell Jar for pointers to resources.

What other hardware?

I also made myself a sump for the vacuum chamber, in case plaster or alginate overflowed while I was degassing. Last thing I need is TufStone in the middle of my nice, new, expensive vacuum pump. It's just a spaghetti sauce jar with two hose barbs cemented through the lid. It goes in a PVC cylinder to catch shards if it ever breaks.

If you didn't buy your vacuum chamber and base, you need also to decide where to run the vacuum hose to: the chamber or the base. I chose base, to allow changing the chamber if I wanted. My one art metal casting course had a chamber with the vacuum hose attached to the chamber, which obviated the need for an extra sump to catch spills. Your call.