Make a two part reusable mold using plaster

Picture of Make a two part reusable mold using plaster
Before I start, I'd like to note that this is my first instructable so please excuse any potential gaps in logic I made and some of the blurry pictures. I tried to take as many photos as possible and will explain the process as thoroughly as possible, but should you require additional help feel free to mention it in the comments below.

So What I've done here was develop a cheap way to create molds for various casting projects. Depending on what materials you already have available, the total cost for creating a single two part reusable mold will range from 0-25$.

The advantage of a two part mold over a one part (where molten material is poured into an open mold) is that much more structurally complicated objects can be duplicated in this way. To demonstrate the process for the instructable, I have chosen a sea shell since it is an object that cannot be duplicated with a one part mold system but is very streamlined - it lacks advanced features such as protrusions.

Plaster is an ideal material for this project as it is very malleable in its unhardened shape, and can withstand very high heat when dry. Therefore, finished molds will work for almost any casting material - I preferably like to create projects out of wax, tin, silver, and gold as these materials are very easy to work with. For this project, and for cost issues, I will make a casting in wax.
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framistan1 year ago
I once molded a chess pawn similar to your method. Fortunately, it was not valuable, because the "professional" mold release spray didn't work at all. My pawn was sealed halfway into the plaster like LUKE SKYWALKER in carbonite! I notice you used SOFTSOAP. I will try something like that next time.

FIY it's Han Solo in carboite

FYI it's FYI

i know sorry

Steelersfan436 months ago

Could you use this technique in making ballistics gel molds?

Excellent instructable, I am eager to give this method a try. Would you recommend using a mold release on the plaster when using metals instead of wax?
armorlord (author)  troopersmachine1 year ago
If you can find a temperature resistant mold release, It would definitely be a good idea.

For me, since I already built enough experience to make perfect molds without imperfections, I just use them as one timers. Cast in the metal, then break the mold. I find it easier to create a new mold than mess around with trying to preserve it in perfect shape, especially for complicated shapes.
Yeah, that's so true, when i do a one time cast, I make single-use molds, but when I make a mold that I want to cast several times in, I have to go with a 2 part, reusable mold. Another minus with single-use molds, if you poured the metal incorrectly into the mold, you can't cast it again, you just wasted: plaster, time, and metal, but with a reusable mold, if you messed up the metal pour once, you can always try again. I tend to make reusable molds for small casts like marbles, but for big intricate casts, I make single use molds, since I know I don't need more than one. Also, what metal do you usually use, I use pewter, zinc or lead, all of them have a minus though, zinc is nontoxic, strong, but it decreases in size greatly as it solidifies, leaving a bad cast, also, zinc is hard to melt on a stove, I prefer a propane torch on a crucible, it leaves the metal molten for long enough to pour cArefully. Pewter is nontoxic, safe, easy to melt, but its very soft and it easily is bent and pewter at times can be pricy. Lead is easy to melt, pretty much cheap, not too expensive, but it is very toxic and carcinogenic, resulting in a cast that you cannot play with to much with your hands. Sorry for long post, thAnks for reading, goodnight to you.
Nice instructable.

An important step is to wet the plaster mould with water than drain it before pouring in the hot wax - otherwise the hot wax will stick to the dry plaster.

shaddoty1 year ago
can this plaster take 480F
armorlord (author)  shaddoty1 year ago
I use these plaster molds to cast molten silver and gold, which I use oxyacetylene to melt. Yes it can take extreme temperatures - just make sure to heat it gradually, preferably using an open flame torch. If you subject plaster to an extreme and sudden temperature change it will crack.