Introduction: Piggy Baby
Babies are cute. Animals are cute. Babies with animal parts are cute--or maybe just odd, depending on your point of view.
So this is how to make a baby with a pig's foot. Or really, this is how to cast a plastic pig's foot (or anything else), which you can attach to a baby doll (or anything else). This is simply a specific application of a casting technique that enables you to build molds and cast parts from live and not-so-live parts, which you can then use alone or combine with other objects to make whatever you want.
Step 1: Materials
Note: Polytek is a good source for casting/moldmaking materials--they're extremely helpful, happy to answer any questions, and they can tell you what materials/techniques to use for almost any casting project--but you could get similar materials from a variety of resources.
For Plaster Cast:
Alginate (such as Hydrogel N)
Plaster (the cheap stuff will do)
Plastic or metal conainers (such as disposable aluminum baking pans)
Needle and thread or fine wire
Pig's feet (or other part to be cast) (many ethnic markets have fresh pig's feet available)
Whisk and plastic or metal spatula
To Prepare Plaster Cast for Mold:
Plaster sanding screens
For Rubber Mold:
Plywood, MDF, or other wood
Wood or drywall screws
Release agent (such as Pol-Ease 2300)
Pourable polyurethane mold rubber (such as Poly 74 or 75 Series)
Plastic or metal spatula
For Cast Part:
Pourable polyurethane casting plastic suitable for rotocasting (such as Poly Plasti-Flex Liquid Plastic for flexible parts)
Paint or dyes
Plastic or metal spatula
Paper towels and clean-up substance recommended with rubbers/plastic, such as denatured ethanol
For Final Product:
Baby doll (preferably with soft body and plastic/vinyl arms/legs/head)
Zip ties, rubber bands, or other attachment mechanism suitable for doll/part
Read and follow all directions and precautions found in material safety data sheets, technical bulletins, and labels. Seriously.
Step 2: Prepare the Parts for Casting
Attach the flat side of your part to the bottom of your container with thread or wire so it doesn't move or float up. Leave approximately 1 inch of space on all sides so the walls of the alginate mold will be thick enough to support the plaster.
If you have only a small hole made by the wire or needle and thread, don't worry about sealing it--the alginate probably won't leak.
Since the alginate will set quickly, ensure the parts are flat, attached and ready to go before mixing alginate.
If your pig's feet have been cut in half (like mine), cast two. You can join them together to make a complete foot later.
Step 3: Mix & Pour the Alginate
Mix the alginate with water according to the instructions. For Polytek Hydrogel N, combine 3 parts of water with 1 part of Hydrogel N by weight (approximately 1:1-1/4 by volume). Be sure to mix enough to totally cover the part.
Since the alginate is very light, a whisk works well to combine the components. Note that you'll have a fairly quick work time (5 minutes for Hydrogel N), so combine well, but also combine quickly.
Once combined, pour the alginate mixture over the part, ensuring the part is covered by at least 1/2 in. on top. If it looks thin on the top and you can still see or feel the part, cover with more--the second batch will still stick to the first if you pour more on within 5 minutes. Don't skimp--since what is now the top will become the bottom of the mold, you want to ensure it's thick enough so it won't break, tear, or deform.
Step 4: Set & Demold the Alginate Mold
Allow the alginate to set (usually about 5-10 minutes)--as it sets, it will change from a liquid to solid with a firm tofu-like consistency.
Once set, turn the container over and cut or remove the thread or wire holding the part to the bottom of the container. Then cut away the bottom of the container (if possible) to remove it; if you can't remove the bottom, invert the container and remove the alginate mold (and part).
Once inverted, gently remove the pig's foot (or other part) and discard the foot.
Since the alginate mold will dry and deteriorate fairly quickly, move on to the next step quickly.
Step 5: Mix & Pour the Plaster
Mix plaster and cold water immediately after alginate mold is set. Mix plaster and water with your hands or with a rubber spatula until well combined and it reaches a pancake batter-like consistency. If you get distracted and the plaster starts to harden before you've poured it, throw it out and mix fresh plaster--don't try to add more water to soften it.
After mixing the plaster, pour it into the alginate mold and fill to the top.
Tap the sides to release any bubbles in the plaster--if you still see bubbles on the top, you may need to pop them.
Step 6: Set & Demold the Plaster Casting
As soon as the plaster has set and is dry (you may still feel some moisture in it) remove the plaster part from the mold--don't worry about tearing the alginate mold--you won't need it again.
For a relatively small part, it may take as little as 45 minutes to an hour for the plaster to set enough to remove it. Keep an eye on it and remove the part as soon as it's dry--don't wait until the next day, since the alginate will continue to dry out.
Discard the alginate mold and put the plaster casting aside.
Step 7: Prepare the Plaster Casting for Molding
To get the plaster piece(s) ready to make your rubber mold with, you'll need to:
1) Shape and join the parts--for instance, my pig's feet came as two halves, so I cast two halves and then glued (with wood glue) the two plaster halves together. After glueing them together, I then used plaster sanding screen to shape the foot, getting rid of the excess where the two pieces didn't come together perfectly.
2) Seal it--since plaster is porous, you'll need to seal it with several coats of shellac or another sealer (I used three coats of shellac). Simply brush on the shellac and let it dry according to the usual instructions. Be sure it is completely dry before working with it, as the shellac will pick up fingerprints and debris, ruining the fine detail you get from an alginate mold. Shellac also sticks vigorously to many rubbers, so you may also want to rub a coat or two of wax over the part once the shellac is dry to both improve the seal and decrease the chance it will stick to the rubber for the mold.
3) Cut or sand off the end to create a flat surface to place against the bottom or the mold so it stands upright--you can use plaster sanding screen if the base isn't too uneven, or you can cut off the bottom of the part with a small, fine hand saw and then smooth it with sanding screen.
Step 8: Build a Box Mold
Once the plaster part is prepared, measure the part. Add 1 inch total to the length and width and a couple of inches to the height to determine how large your box mold should be, as you'll need to leave 1/2 inch around all sides for mold walls.
For instance, if your part is 2 inches wide, 3 inches long, and 8 inches tall, you'll need to build a box mold with interior dimensions of about 3 inches wide by 4 inches long by about 10 inches tall (1/2 inch, plus some extra to keep everything inside).
To build box mold, cut a mold base plus four walls to the appropriate dimensions out of plywood, MDF, or any other wood you have available. Simply screw the walls together to form a square with basic butt joints and screw the box to the base, so it's enclosed on 5 sides.
Step 9: Prepare the Box Mold
Apply 2-3 coats of shellac with a brush to the interior of the box to seal it, letting each coat dry before applying the next.
Seal any gaps at the corners of the box or where the base meets the walls, with an oil-based, sulphur-free clay that won't react with the rubber you'll be using (such as Prima Plastilina).
Attach the sealed plaster part to the bottom of the box with a piece of clay.
Spray the interior of the box thoroughly, including the plaster piece, with a release agent (such as Pol-Ease 2300). Be sure to get all of the corners, undercuts, and other places rubber might find a place to steathily stick to.
Step 10: Mix & Pour the Rubber
Get out your scale, three plastic mixing containers (two of the same kind for parts A and B of the rubber, plus a third container to transfer your mixture to), a rubber spatula for mixing, and a big pile of paper towels.
Put down some kraft paper or plastic to protect your work surface and put on gloves to protect your hands.
Label one container "A" and one "B" to keep your components straight.
Place a container on your scale, and zero the scale.
After reading the instructions for your rubber carefully, weigh out the appropriate amount of each component (for Polytek 75-60, 1 part of A to 1 part B, by weight) into the marked containers. Be sure the combined volume will be sufficient to well cover the part.
When you and the box mold are both ready, combine parts A and B of the rubber as noted in the instructions for the material (for Poly 75-60, pour part A into part B), and stir thoroughly with a rubber or metal spatula. Once combined, scrape the mixture into a clean mixing container and stir again to ensure it's completely mixed.
Immediately pour the mixed rubber into the box mold, filling it at least 1/2" above the top of the part.
Step 11: Cure & Demold the Rubber Mold
Allow the rubber to cure for at least 24-48 hours (or as directed in material instructions). To demold, unscrew the parts of the box mold and remove the rubber mold.
Turn the mold over so the base of the foot is at the top, and insert the blade of a utility knife into the side of the mold at the top at the until it reachs the plaster part inside. Start a cut and allow the knife to move (more creating a clean tear than making a cut) all the way around the mold in one continuous cut, splitting it into two halves.
Once it's in two parts, remove the plaster part.
Step 12: Prepare the Rubber Mold for Casting
Before you can cast the plastic part, you need to make a cap for your mold. Coat a piece of scrap wood (large enough to cover the opening that was formed where the plaster part met the base of the box mold) with shellac. Once dry, apply some petroleum jelly to it to help create a seal when applied to the mold.
Prepare the mold and cap by coating thoroughly in release agent. Find two (or more) rubber bands and ensure they can hold the two pieces of the mold together firmly when placed around the mold.
Place the rubber bands around the mold, keeping them out of the way of the opening, which you should orient to the top, and keep the cap handy.
Step 13: Mix & Pour the Plastic
Note: The plastic sets very quickly, so you'll need to work very quickly--make sure everything is ready for this step and your mold is completely set up before beginning, or your plastic may end up setting in your mixing container, not your mold.
Get two mixing containers (that are the same) and your scale.
Label one container "A" and one "B".
Mix your plastic as indicated in the directions. For Poly Plasti-Flex, mix 35 parts of A to 100 of part B--but note that part B is very viscous like marshmallow fluff, making it difficult to pour, so add A (which is lquidy) to B and mix thoroughly. Mix enough to fill the mold approximately halfway full if rotocasting, or totally full for a solid part.
As soon as it's mixed, fill the mold about halfway full with the plastic, attach cap, and rotate mold extremely vigorously for approximately 10-20 minutes. You may need to shake it in each direction initially to ensure you get it into all the corners, then continue to rotate to get an even coat. You'll be able to see the white plastic through the amber mold, so try to check that there's white plastic everywhere it should be.
Work quickly, as the pour time (the time you have to work with it after parts A and B meet) specified for Plasti-Flex as just 3 minutes.
Step 14: Set & Demold the Plastic Casting
Allow the mold and part to set for about 30-45 minutes, then remove the rubber bands, separate the two pieces of the mold, and remove the cast part.
After your first cast is complete, you'll probably have to slightly alter your technique, waiting time, or amount in order to get the type of part you want, so simply repeat steps 12-14 as many times as necessary.
Step 15: Attach Plastic Part to Doll
Find a baby doll that you think would look good with a pig's foot or two. Dolls with soft bodies are much simpler to attach the parts to than dolls with plastic bodies, as you don't need to as precisely match the part to the available opening.
After selecting a doll, remove the part(s) you wish to replace, and put the cast part in its place. Attach using any mechanism that will work for your doll. Zip ties and rubber bands work in many cases.
To make it more realistic, you may also wish to air brush the part you've made to match the rest of the doll. Depending on the clothing of the doll and the placement of the part, you may also wish to alter its outfit.
Step 16: All Done