Some of these pics are big, sorry. Too lazy to resize...
Arms and hands are (like all the other parts) a world unto themselves. So here we go...
The above pic is based on that good ol' scale drawing you've created a while ago (see why it's so important to have that life-sized drawing?) You need to use that scale drawing to figure out the exactly size, shape, length, and overall look of the arm and hand for your character. As you might expect, it needs to be to scale, once again. To arrive at this drawing, I "light tabled" from the original scale drawing to get the arm and hand figured out... then from that drew in what the armature would look like.
You'll notice there's some square brass stock at the end of the arm. That's to slot into the chest armature. Further, you'll see the length of the arm is braided 1/16" armature wire, with some epoxy for the arm bones, and epoxy for the hand (into which is embedded pieces of thin floral wire for fingers). The skin over top is liquid latex (which I haven't talked much about yet, but will).
Floral wire is nice for fingers. It's strong, will stand up to the animation fingers need to do (detailed, precise movements) but is still easy to animate. You don't want really thick wire for fingers, as it will be hard to animate.
Since both of the characters arms were the same, this one scale drawing will serve. Just keep referring back to your scale drawing of the arm armature as you cut pieces and mix epoxy, so that you are making the arm JUST the right size. It's easy to drift, so use that drawing to check. After you make this basic arm and hand, you can simply bend the fingers which ever way you want, to craft it into a "right" arm/hand or a "left" arm/hand.
The above pic is the puppet arms in progress. It's darn handy to use clothes pegs to hold the arms up safely as each coat of latex dries. And another tip- don't apply the brass stock till the arm is 100% done. If you put it on earlier, it's quite tricky to figure out the exact arm length. Leave yourself extra wire at the end of the arm, make the arm, apply all the latex, then snip the wires to length, then glue on the brass stock.
Gluing tip for armature wire when attaching it to brass stock- use "gap filling glue". It's very strong, and will expand as it dries, hence the name. Regular Krazy Glue is super strong, but will only bond surface-to-surface through direct contact. Gap filling glue is the way to go (in this case).
The process for putting on the latex is TRICKY (notice all the caps. I must be SERIOUS). I've practiced a lot, on various projects, to get to a pretty good point. It takes lots of practice. You'll notice with these arms/hands they need to be smooth from the finger tips right up to the shoulders, (smooth, as in like real human arms/hands) since the whole arm would be exposed. If the puppet had long sleeves, you'd only have to make smooth hands and maybe wrists (and not worry about the arms).
Costume REALLY effects puppet making, in this sense.
It was also a challenge because of the visual style I wanted. The puppet heads were smooth and cleanly sculpted. So the arms and hands had to match. If I had made the heads "rough" in their finish, the arms/hands could have been "rough" as well. "Roughly" applied latex is much easier to achieve, and you can get some wonderful textures by using make-up sponges or bits of foam (thanks to Ted Heeley for that tip). You can get a really nice "smooth but pebbly" finish that looks great under camera. And it has a really warm "Muppet" vibe, like a very dense foam. Really appealing, great texture (and we all know stop mo is all about the textures). BUT my visual style was smooth, so the arms had to be smooth.
A HUGE tip I give students- create a visual style that allows your puppet to have a rough finish, and you will be MUCH happier. But- smooth is possible, if you are brave enough. Or stupid.
Here's the finished arms (pre-brass stock). Note their smoothness. Hard-earned, right Carla? And another tip- once you are 100% done applying latex, dump some baby powder on the arms. Rub it in, and it takes any unwanted stickiness away from the latex, and gives it a very pleasant matte finish (latex errs towards shiny- baby powder it away). And besides, you get a sweet-smelling puppet. Win-win.
Here's how I got them smooth. I used a small, cheap brush to get the first layers of latex on. A coat of latex... let it get pretty much dry... then another coat... it takes time. There's lots of tricks and tips for using liquid latex, you can find heaps at stopmotionanimation.com
I used this process to get the arms basically "on their way". By that, I mean at the joints (elbow, wrist) I used this process to add lots of layers of latex, so I had a nice smooth tube. In other words, if you ran your finger from the wrist all the way up the arm, it was flat- no dip inward at the joints. Now, with that basic "tube" of an arm, I switched techniques. I now started "dipping".
You can only get so smooth a finish by brushing. The bristles ALWAYS leave a path as you draw the brush up the arm, leaving grooves and streaks. But dipping means no brush is used, so there's nothing to leave a mark.
To dip, I found a bottle (baby food) that was deeper than the arms were long. I filled the jar with latex, tinted it with the skin colour (acrylic paint), held the arm by the end wire, and dunked it, fingers first, into the latex. Then I pulled it out, fast, being careful not to bang the arm or fingers on the jar mouth.
I quickly flipped the arms around so the fingers were point up, and used a small brush (and often a toothpick) to carefully "urge" the latex downward in the spaces betweens the fingers. Without doing this, you'd get really stubby, web-like fingers. A toothpick works well, cause right after you dip there is SO much latex it can be moved around without leaving streaks. And with the fingers pointing up, you let gravity help.
The next step (once you're sure you aren't going to get stubby fingers), is to rest the arms. This is when a pair of "helping hands" is, well, helpful. Because you want to be able to tweak the angle at which the arms are drying, as they dry. This way, if you see the latex is "sagging" to the underside, you can flip the arm to balance that out. Helping hands are fantastic for this. As the pic below illustrates:
And here's how the finished arm fits into the armature:
Finally, this is a REALLY important aspect of using latex for arms and hands. The brand makes a HUGE difference. I've used other types of mould maker's latex (which is what this material is usually called at the art store), and they suck. They are too thick, too "chunky". You CAN water latex down, with (duh) water, but still... The best brand is this:
Burma Brand latex. End of story. It's lovely and thin, paints on really easy, absorbs acrylic paint (for tinting) really easily, and is great for dipping. It's THIN, and that's how you get SMOOTH. Only use this brand.
Other brands are ok for rougher finishes. Only use this for smooth (or another brand that's equally thin, but I haven't found one).
After all this, here's my two cents of puppet making for those that are serious: come up with a design that is "rough"- a creature of some sort, an alien, a monster, it can be cute, scary, sad, silly, whatever, but let it rough in its design. You can then make some MARVELOUS puppets (I see students do it every year), if you keep it rough in it's finish. That way, you wind up with an awesome looking puppet, and learn about the materials (specifically latex) as you go... then attempt smooth with the next puppet.
On the other hand, now that you know about dipping (after this entry), maybe you'll be smooth right away.
Good for you! But you owe me 5 bucks now.