Mutant Fetus / Alien in Jar Tutorial

i’m here to present a little bit of a how-to on making realistic specimens in jars. Before we begin though, let me point out that this is not going to be a really cheap project. The materials and processes can get kinda pricey, but it definitely shows through in the finished product.

Alright, here we go. Once you’ve got a well-developed idea and have done drawings and some anatomical research, you’re ready to sculpt your specimen.

I sculpted mine with Chavant NSP (Non-Sulphurated Plasteline), built over a wire and tinfoil armature. I tried to make it all in once piece, without the legs sticking out at odd angles, so that I would minimize undercuts in my mold. After I got my basic form the way I wanted, I very carefully went over the surface of the clay with a blowtorch to melt it a little bit and give it a super smooth glossy finish. For some detailed areas that needed more smoothing, I used Isopropyl Alcohol and a soft brush.

Here’s my finished sculpt:

After your sculpt is completed, you’ll want to begin making your mold. I used Ultracal 30, a type of industrial gypsum plaster cement, to make my two-part mold. Mold-making is a whole other tutorial entirely (which I might get around to writing sometime later) so I’ll link you to a couple of decent introductory tutorials I found online:

1. 2-part Plaster Mold Making
2. 2-Part Master Mold Making from Toy Mania

Hopefully those will explain what you need to know. Just be aware that because of the materials we’ll be using later on, it’s really important to have a decent-sized vent coming out of your mold. I used the tail as a vent so that I wouldn’t have to worry about covering the seam later.

Now that the mold is done, it’s time to try casting a specimen. Using slip casting latex, stipple in a light layer into each half of the mold. This is going to wind up being the outer skin of the specimen. Once it’s dry, close the mold up, clamp the two halves together, and you’re ready to move on to the next step.

The inside of my specimens are made from an two-part expanding polyurethane foam. I used Flex Foam-iT V, made Smooth-On. You can order it directly from smooth on It’s really simple to use, since you just mix the two parts 1:1 volume. This starts a chemical reaction that causes the product to foam and cure once it’s expanded fully. Mix the foam quickly, and pour it into the vent hole in your mold, making sure to shake your mold a little bit to get the chemicals all the way down into the bottom of the mold so you don’t get big air pockets.

Be sure that you’re working in a well-ventilated area and that you have proper protection while working with this foam, since it’s pretty toxic stuff. Let it cure for about a half hour to an hour, and then you can de-mold. Brush some ba powder or corn starch onto the surface as you de-mold so that the latex doesn’t stick to itself.

Carefully trim off any excess latex around the seams, and you’re ready to paint. I used acrylic paint thinned out with Isopropyl Alcohol. I started stippling in a mottled skin pattern, with lots of yellows, oranges, pinks, and reds. Then using a really thin wash, I put in some blue veins. The purpose of doing the thin wash is that it makes the veins appear to be beneath the surface of the skin. The same thing applies with the pupil.

(Below) Here are some painted specimens

Next, I dipped each specimen in casting latex (the same latex that we used for the skin earlier). This will seal the paint in, and will also give it a bit of a translucent skin, which adds a lot of realism.

Now it’s time to make some umbilical cords. I made mine stippling a sheet of latex onto a smooth table. Windows, mirrors, smooth floors, etc. will also work, the point is just to have a nice big flat surface to make sheets of latex on. Once you’ve painted on a layer or two and it dries, start peeling it away and twisting as you go. The latex will stick to itself and become a gross twisty umbilical cord. I used hot glue to attach my umbilical cords to the specimens.

Now, just find a good bottle or jar for your specimen. I filled mine with a mixture of yellow food color (for that nice formaldehyde look), water, and Isopropyl Alcohol (to keep bacteria from growing inside the jar).