Replicating Body Parts in Plaster




About: independent filmmaker, pop-cultural theorist, puppeteer.

This is the first part of a two-part series on making a silicone replica of a body part. However, before we can make the silicone replica, we'll have to make a plaster replica.

*** WARNING: Because of the body part chosen for casting (in this case, a woman's breast), this Instructable may contain material considered offensive or objectionable to some readers. Viewer discretion is advised. ***

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Step 1: Gather Your Materials

To do this step you will need the following:

1) Dermagel - at least 2 pounds (or equivalent dental alginate)
2) Plaster - at least 2 pounds
3) Plastic container for placing body part inside of
4) 2 plastic mixing bowls - preferably with measuring lines (might get ruined)
5) Plastic cups for pouring materials
6) Duct tape
7) Metal whisk
8) Wooden mixing stick
9) Gram scale
10) Box cutter
11) Flathead screwdriver
12) An old towel
13) An assistant (optional, but highly recommended)

Step 2: Select a Body Part

This is the fun part.

The first thing you'll want to do is decide what to replicate. Some things are clearly more challenging than others. For instance, casting a finger is definitely easier than casting one's right breast.

However, I say go with whatever will make you or your robot happy.

Step 3: Prepare Your Container for Casting

Once you have decided what you're going to cast, you have to figure out how to cast it.

If you're casting something that you are capable of sticking into a bucket (i.e. a hand, foot or elbow), then all you need to do is find a container slightly bigger than the part you are trying to cast.

If you're casting something like a boob or a belly button, then you have to find a container that will fit nicely over the entire area of the body part.

For my first cast, I tried using an old yogurt container that was cut in half (below). This container cut off part of the breast. So I tried again by cutting in half a two-gallon water container and that was more than large enough to cast the body part (not shown).

Step 4: Other Prep Work

The dermagel mixes 1.5 water to 1.0 of the alginate by volume.

In other words, there is one and a half times water than there is alginate (to begin with).

Since the water is poured first, now would be time to measure out as much water as you think you will need (keeping in mind that the alginate will take up some additional space in the container).

Once that is done, you are also going to want to give the dermagel container a couple of good shakes to break up some of the bigger clumps.

Step 5: Attach Your Rig

If your rig for casting requires any special attachment to your selected body part, you are going to want to attach it before mixing the dermagel. Place the rig over the body part, making sure that its walls are not coming into contact with anything they shouldn't (i.e. anything that will interfere with the casting process or that will ruin the outcome of your cast), then tape it in place with duct tape.

Make sure that all edges are well-sealed with the tape or your rig will leak, creating not only a terrible mess, but also potentially traumatizing the person being casted (dermagel is cold, and has a thick, slimy consistency). If you're being body casted anywhere but an appendage that can just be shoved into a container, leakage is not pleasant. When in doubt, use more duct tape than less.

Step 6: Mix the Alginate

Mixing the dermagel (dental alginate) is not quite an exact science. Although, it is fair to start with a base mixture of 1.5 parts water to 1 part dermagel by volume.

Once you have that base, mix thoroughly and see what the consistency looks like. Ideally, it'll have the consistency of cake batter. If it does not, add more dermagel until it does.

Mix vigorously until there are no clumps left.

It's important to know that the warmer the water is, the quicker the setting time will be. This could be helpful depending on what you are casting.

Figure that the normal setting time is between 15-30 minutes to be on the safe side.

Step 7: Pour and Wait

Slowly and steadily pour your mixture into the rig.

Once all of it has been poured and/or it is filled to the top, sit and wait. Hold as still as you can.

In about 15 minutes, touch the top of the dermagel and see if it is solid. If it is solid, give it a few more minutes to be on the safe side.

When the time comes, slowly remove the tape and peel the mold away.

(It is important to note that if you plan to attach the rig to a part, dermagel gets heavier and expands as it hardens. If the rig that you are using to cast is big, and requires a large quantity of dermagel, plan to be able to properly support it, or else risk 1: the tape/support system ripping off/breaking and the rig tearing off before the dermagel has time to harden, 2: the rig shifting during the hardening process, and the outcome of the mold ruined. You should be able to get a sense of this when you are pouring the dermagel into the rig. If, during that point, the person being casted is already having difficulty supporting the rig him/herself, or can sense the support system failing, consider an alternate method of casting the part or just quickly reinforce the rig.)

Step 8: Plaster

Since dermagel degrades relatively quickly, you'll probably want to pour the plaster into your mold as soon as possible.

The plaster I used is measured by weight in a ratio of 45 grams of water for every 100 grams of plaster (however, you are going to want to check the specs on your plaster). Once you have measured out your water and your plaster, mix them together until you have a toothpaste-like consistency.

Pour the plaster into the mold. You may need to use a spoon or wooden stick to scrape the plaster out of your mixing bowl into the mold. Try to fill it as best as possible.

When the plaster is in the mold, give it a couple of gentle taps against the ground to raise possible air bubbles.

Lastly, I added a few L-brackets and screws to the back before it dried completely so that I could suspend it from strings if need be while silicone casting in the next step. It is helpful to have at least three points of contact.

Step 9: Peel

After an hour or two your plaster should be dry.

Peel it from the dermagel mold and admire your handy work.

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    227 Discussions


    6 years ago on Step 9

    if you want to reduce the amount of alginate you use you can always use plaster bandages for backing and to reduce bubbles try not to whip the alginate before applying it on the body. oh and for the person that asked about casting the lower extremities it is very possible but time is limited!!!! you can do a man but you have to prepare a container ahead of time and have him at full attention when the alginate goes on because it can be quite cold. you are also able to buy these kits on line complete with instructions. hope this helps

    5 replies

    Reply 5 years ago on Step 9

    I want to do a full chest with both breasts. Do you suggest making a container like this, or just apply the alginate and wrapping with plaster bandages like for a face?


    Reply 5 years ago on Step 9

    I have observed the person getting the mold done. Some times just having them sit upright can work but remember that alginate is heavy and can stretch the skin of the breast. Some times it is able to work by making a container that the person can lean into or lie on top of. Fill it with alginate and position them over the container. After it activates remove the person and fill it with plaster or wax to get your finished piece. Every chest mold for women is different some you have to have sitting some have their hands above their head. Position them and put a slight pressure on each breast and see how much give there is. If you dont want a fold on the underside of the breast then having them put their hands above their head might help but remember to have someone help support their arms while you work. It is a tough job for you it is also a tough job for the model to suspend their arms in the air for that long as well. Just observe each model and try various poses each time applying pressure downwards on each breast to make sure that is the position you want them.


    Reply 5 years ago on Step 9

    If you want to do a full mold of a womans chest there are several ways to do it but all of them require the alginate to be smeared on and placing bandages in a "old style I form" across the chest before applying the other plaster bandages are put on for the shell. This added support allows the bandages to form to the curve of the breast giving you more real look and not short changing the subject of their true body shape. As for the different poses you will have to practice this part before doing the cast. Have your subject raise their arms above their head and gently press down on the top of the breast. This will give you an idea of how much stretch you will have when applying the alginate. Some models you can have with their arms proped up with two chairs. If you are lucky enough to find some one that can have their arms by their side and not have any droopage then you have found a one in a million. Other than that you might have to try laying the person down on a table or floor to do the mold. With this method you will have the breasts go to the sides and might not look right. Basically you will have to try a few different poses through trial and error. Hope this helps


    Reply 5 years ago on Step 9

    I have done breast molds but each one is different. Some women you could pose them with their arms in the air or out to the side, some you have to get them to lay down to get a proper mold. The alginate is heavy and will weigh on the breast giving you a distorted look to the final outcome. The first thing I do is test the area by pressing on the top part of the breast seeing how much it stretches. You don't have to press hard or use your full hand. The side of your hand pressing down like you were wiping something off. Go slowly and you will see how much give is in the area you are molding. If the models breast is very soft then I would recommend that you have her lay on her back to do the mold. Remember Vaseline is your friend. Women have hair on their chest it is very fine but it is there and can rip out the same as eyebrows!!!! Remember they have to be comfortable if you want them to ever do another mold for you? After that just do a mold the same as a face mold. If you are laying in burlap to hold the plaster bandages to the alginate then also don't forget to lay a strip between the breasts for added security. Other than that I would love to see the final outcome. Happy molding!!! :)


    3 years ago

    This may be a dumb question, but hot hot a material could i use against the plaster?
    Either to make a new mold, or for inside a plaster mold?


    11 years ago on Introduction

    Now i would like to find out how to make a cast of the triangular section between top of nose and base of chin. It's to make a proper breathing mask. Also possibly a cast of my right arm, though that might be a bit gruesome as it might be coming off though i think it's too late for that. Crikey, that sounds morbid. Oh i seem to recall seeing a piece that was made up of sections of the female human body. The pieces were separated by gaps and held in place by an armature which put me in mind of a spine. It was quite brilliant evoking, as it did, the movement of a swimmers body through water.

    2 replies

    Reply 10 years ago on Introduction

    Sorry to hear about your arm I hope it works "worked" out for the best .That's a good idea about the custom breathing mask .It should be more comfortable .You would need at least one helper you really trust ,what kind of breathing tubes would you use while letting it set up ?


    Reply 3 years ago

    randomray never use any tubes when doing a head cast. If you put a straw or tube in the mold you run the danger of the alginate dragging the tube out of the orifice you have it in. Long story short your model will not be able to breathe. Easy fix when molding get the subject to blow the alginate out of their nose after you put it around the nose. This creates a air hole that they can breathe out of. Much easier and you dont run the risk of hurting your model or yourself.

    Mr Rancher

    6 years ago on Step 2

    Hahaha, great choice of sticker.
    Nice touch.


    7 years ago on Step 9

    Didn't you say you were going to silicone-cast it?


    7 years ago on Step 7

    It may feel heavier but not possible to get heavier. How would that happen?


    7 years ago on Step 8

    Might as well stick your mold back in the plastic cup to keep its shape while casting it. Your plaster is way too thick, that traps air pockets.


    7 years ago on Step 9

    To avoid air bubbles you want to work with thinner alginate, 'scrub' the breast with a gentle tool while submerged, and your plaster should be like tomato soup when you first mix it, not like toothpaste.


    7 years ago on Step 6

    I think I'd go with faster set time/warmer goop.


    7 years ago on Step 5

    It is normal to mix the alginate with tepid water!


    10 years ago on Step 2

    D, how would you recommend doing nipple only? Method & Materials? Thanks!

    1 reply