I've been on a "things in a bottle" spree for about a month, cranking out Halloween decorations for friends looking for something to add to a shelf display or mad scientist's lab. In the process I've picked up a few more refinements to the "Making a Thing in a Bottle" tutorial and its followups (here and here). Eventually I'll get around to redoing the whole tutorial, but for now I just wanted to add a few short notes.
The parasite pictured above has teeth made from epoxy putty, but the rest of the body is a latex skin over a silicone core. While the skin does use some maskmaker latex the rest of the body materials are right off the shelf of the local home store- waterproof silicone caulk and latex carpet adhesive. The latex was brushed on a master form made from hardened polymer clay, allowed to dry, and then another layer was applied. Once the skin was thick enough it was dusted with talc and gently pulled off the form, getting turned inside out in the process. The skin was then filled with silicone to give some firmness.
Why go with soft materials instead of sculpting the whole thing from Sculpey or epoxy putty? Because it's more survivable. It's inevitable that your thing is going to bang up against the inside of the bottle while it's being handled. If the body is soft the force of that impact dissipates harmlessly. A hard, brittle material like hardened polymer clay will eventually get damaged, especially if you have fine projecting detail.
You could, of course, use a real casting silicone to fill the body, but that's needlessly expensive. Besides, you need the caulk to run a bead along the bottle lid to make sure it stays sealed forever.
This section of the parasite came out phenomenally well, and it's all thanks to Tom Banwell. Last year he did a post on how to make a quick and dirty slush casting of a tentacle. This entire section was made using that technique. The end of a pipe was pressed into a glob of clay to get the general shape and then dental tools were used to sculpt a negative impression of the detail. Layers of latex were then brushed in and allowed to dry, forming the skin. The latex "mouth" was then removed from the clay and cleaned. The epoxy teeth were added by hand punching holes in the skin, inserting the teeth from the inside, and then brushing a layer of latex to hold them in place. Once that was dry the mouth was attached to the body with another application of latex.
Almost all of the coloration for the critter is integral to the latex- light washes of ivory, yellow, and brown were applied between coats of latex, locking the pigment into the skin and producing a very organic, translucent effect.
I'm sure I've made this seem overly complex, but it's actually a pretty simple process. Best of all, you can do it using inexpensive materials before investing in more expensive alternatives. If you just want to bang out two or three specimens it shouldn't cost you more than $15 to pick up latex carpet adhesive, a tube of bathroom silicone, and some epoxy putty. If you're happy with the results you can look into upgrading to mask maker's latex and maybe pick up a tub of Aves Apoxie sculpt (an awesome putty you can find over here).
Finally, there's always the Ebay option if you just want a nifty bottled specimen and don't want to do it yourself.