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.

Step 1: Materials

The materials listed here can be easily interchanged with others of similar properties. Get creative! instead of buying what I listed here try to find alternative supplies

Materials needed for making the mold:

an object to duplicate - make sure it is something you can sacrifice in case of a screw-up :)
a generous amount of plaster of Paris
Hot glue, or any glue that can be easily removed when dry
Play doh or modeling clay, or any other material with the same consistency 
Soap (to act as mold release) - there is also professional mold release spray that can be bought from eBay or amazon
paintbrush, or any tool to spread mold release
a plastic box, or four strips of plastic or other material that can be glued together to make a hollow box
portfolio paper cover, or a paper plate, or anything other than newspaper to serve as an overspill guard

Additional materials to make a wax based duplicate:

a large candle, or any excess wax
cooking pot and stove
boiling water
I did this with a wax indeed but didn't make two halves it's a destructive mold will the mold explode whe silver is poured in because of moisture?
<p>If you preheat the mold, this shouldn't be an issue. I'm not an expert on the subject but I've read that they preheat the plaster molds almost to the temperature of the molten metal to prevent thermal shock but the mold is also broken to get the part out. They were casting iron with the lost wax method of making the molds.</p>
<p>I am not sure why you need playdough. Can't you just make the first half mold using plaster? I guess not but I am not sure why. <br><br>Also, as <a href="https://www.instructables.com/member/joemellin" rel="nofollow">joemellin</a> says, the need for a &quot;spill guard&quot; is unclear. Why not just use a tupperware (as you did) and keep the bottom intact, grease oil or soap it and prize the first half out of the still intact tupperware container? <br><br>The way I had envisioned is<br>1) fill a tupperware half full with plaster</p><p>2) Press in an object well greased. <br><br>3) (Thanks to you) Add some straws for pouring and some small objects around the half submerged object for the &quot;lego-like&quot; fit. </p><p>4) Wait till solid. Grease/oil/soap again and pour on another half of plaster. <br><br>I am not sure of the need for the playdough. <br></p>
<p> Quote &quot;2) Press in an object well greased&quot; You are suggesting placing the object directly into the wet plaster? This has issues depending on the object being cast. The most obvious issue is the object may just sink into the plaster and be impossible to remove without breaking and therefore ruining the mold. The play-doh is there to help control the mold line.</p>
Hi, I'm going to ale a mold for a bronze casting and am torn about the medium to use. I am casting a finale, a pyramidal shape with a height of about 6 inches, as well as a base width of about 6 inches. I was originally going to cast it using sand, but this method seems far easier, all things considered. Do you think that this plaster method will work with that volume? I think I'll need to make it a three part mold to accommodate the void in it.
<p>I really like your method of creating a seal around each half of the model with play doh. It's so much easier and quicker than trying to cut the shape of the model into a base board and sealing the gaps around the edges after. </p><p>For small models like that shell though, I would suggest using mold putty to create a mold. It's significantly quicker and easier than using plaster which has a tendency to break when de-molding, espiecally from objects with fine detail like that shell. Plus wax is delicate to begin with so fine detail won't survive a rigid mold being ripped off.</p><p>Also worth noting with wax is that it will crack with sudden temperature changes. In other words, don't put it in the freezer to dry quicker or it will fall apart when you take it out. </p>
<p>Thanks for the info. I am planning on doing my first pewter pour of a small art object. I have two questions. Is there a special kind of plaster I should use when pouring pewter? and also. Can I pour into a plaster multi-piece mold? Thanks. Gary O</p>
can this plaster take 480F
It sure can. Once your plaster molds have dried overnight put them in your oven at about 100F after about 20 minutes turn it up to 250 for 15 minutes and work your way up to 400F. This takes all of the moisture out and then the mold can withstand temps up to 2200F.
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.
This was my question, i was wanting a resueable molds that could hold upto at least zinc, but silver and gold even better.<br><br>Are you saying before melting my metal warm the mold? Then melt the metal and pour? I have been plan to do all heating with torch either propain or acetylene i have both.
<p>Before pouring your metal make sure your mold is properly heated. Otherwise the sudden heat shock will cause cracks. Depending on the mold complexity it may require sticking the whole torch inside the mold. With some practice you'll get the preheating concept right. Until then - pour over sand!</p>
<p>Can you use plaster to fill the plaster mold once the mold is set?</p>
<p>If you are talking about making a plaster part using the plaster mold you can. You just need to use what's called potter's soap as a mold release agent. Mix some gooey potter's soap with water, brush it all over the mold, and cast your part. Best of luck with it! It's worked for me in the past. </p>
<p>I use artists masking fluid as a release agent....on the plaster paris only..ie not on the item being molded...it works very very well....also i find coating the surfaces of the molds with polyester resin...which soaks into the plaster and hardens..i find this makes the molds a ittle stronger and more durable..</p>
<p>and...make sure you plaster molds are totally dry before attempting to pour moulten metal....i learned the hardway and got hot lead all over the place...a little went inside my asbestos glove and burned me badly....adding a little salt to plaster speed up drying... </p>
<p>One thing I would recommend when making the mold is to incorporate some kind of vent to allow air to escape as 'molten' material enters, to avoid air bubbles in the new finished item. We did something like this when I was in 8th grade and the vent(s) were required as we were pouring pewter.</p>
<p>Thanks for making this. The bit about the over spill guard is a bit confusing to me. It looks like from the picture of you glueing (because of the reflection) that you are glueing two boxes together, when it seems it is just a 4 sided box and basically making it so that you can switch which of the other 2 sides is inclosed. </p><p>I think a picture where you can tell it is being glued to something / no reflection would be a great help!</p><p>Thanks again for making this, I am gonna go get my mold on :)</p>
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?
If you can find a temperature resistant mold release, It would definitely be a good idea. <br> <br>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. <br> <br>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. <br> <br> <br>
I once molded a chess pawn similar to your method. Fortunately, it was not valuable, because the &quot;professional&quot; 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.

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