How to Make a Mold for Lost Wax Casting




Introduction: How to Make a Mold for Lost Wax Casting

This is the cheapest and easiest method of preparing a mold for lost wax casting. All you need is your wax sculptures with sprues, plaster of paris, water and containers.

Step 1: Make a Plaster Mixture

Use two parts plaster powder to one part water. Most plaster packaging instructions say to mix water into plaster. On the contrary introducing plaster powder to water will minimize the amount of bubbles. So start with water and gradually add plaster. Note- plaster powder shrinks as it soaks, you'll use a lot more then you think so be supplied with a big bag before you start.

Step 2: Stir

You can use a stir stick of some kind but I use my hands to be able to brake up all the lumps fast before the mixture starts to set. Be thorough and add a little more water or plaster until it's smooth and the consistency of pancake batter. If there are bubbles you can tap the bucket lightly on the work surface and watch them raise to the surface and pop. 

Step 3: Imbed Wax Sculpture

Gently and slowly insert your wax piece into the plaster mixture. Sculpture down, sprues up. Sprues should remain visible on the top surface. Your piece should not reach the bottom or any walls of the container. Hold your piece hovering in position until you feel it's being supported by the surrounding plaster. 

Step 4: Allow Time to Set

Allow the plaster to set completely, the longer the better ( I left it overnight).

Step 5: Pop the Mold Out of the Container

For one piece I used a plastic container. For the other which didn't fit into a plastic container I improvised with aluminum foil. Remove whatever you used as a holding vessel and get to the bare plaster mold.

Step 6: Bake the Mold

Even though the plaster mold appears to be dry, there is moisture trapped in it. In order to dry it out and pre-heat it before melting the wax out use a conventional oven and very slowly increase the temperature. Heat shocking it will cause the mold to crack so be patient. Follow my next instructable on burning the wax out of the plaster mold for lost wax casting for further instruction. Have Fun!



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    17 Discussions

    hello im really wondering, how do i actually make the wax, can i
    actually make the wax? in this video it gave me the impression that i
    could make it.
    its should be time stamped so just click on it, but if not go to 5:17.

    The man
    says "2 parts paraffin, and 1 part hot glue". So is it even possible to
    make wax that wont completely meant to the hand and is good for casting?

    I'm very new to this and am a bit lost. :P

    4 replies

    You really didn't answer the question. I am also curious as to how do you make the wax. Or Failing, that where can we purchase it?

    Crayons or cheap candles - just make sure they don't have chalk as a filler

    I'm assuming you mean the item that you want to eventually be made of metal. I had mine 3D printed at my local library, or you can find a plastic and carve or the like, as long as you can melt it out, then you should be good.

    hey Gecko is my account^, i cant be bothered recovering the password, you didnt really answer the question.

    one ever gnawing doubt.. it is said that plaster of paris is a bad mould material if u r casting anything with a higher melting point than of lead.. and disaster for silver or copper.. suggestions?

    4 replies

    Good question! I have casted silver and aluminum in plaster molds with great results. There is a particular method of doing this though: You have to heat treat your molds. For investment molds a conventional oven works well. Over several hours gradually increase temperature to 400 then gradually decrease to cool as to not crack your mold with temp shock. With lost wax without a vacuum chamber you'll have to get it much hotter to burn out the wax. I use a kiln and ever so gradually increase the temperature to 1000 degrees. Then gradually bring down to cool and leave in the kiln over night. It always works despite varying opinions. Good Luck!

    wouldn't it make more sense to cast, high temp metals while they are hot? to reduce the high gradient shock, then reduce the temp gradually? in a kiln with a programmable controller, designed for annealing glass.

    You may not want the metals to cool down gradually, I don't know how aluminum or brass would react, but it could be a factor.

    Is it just plaster of paris, and not a mixture of something else with the plaster? I'm going to be casting with aluminum, which is about 1100 degrees when liquid, so will the plaster take that heat?

    1 reply

    It should, if you cure it properly. You may still crack the mold, but if it has supports (such as the container you made the mold in) you should still get a good cast.

    Nice one! Check my instructable on making a vibration box to get the bubbles out! Thanks

    I know this is two years late. Great Instructable. I have cast bronze and aluminum in a plaster lost wax mold. It's how I originally learned. I've done it for small (jewelry scale) sculptures and larger scale sculptures. The largest size is 18"X18".

    Very informative! I just wish it was longer.

    Wow. Thank you for this write up. I've been looking into doing this for some time (been using lost foam casting) and now this weekend I will try my hand in lost wax casting. Thank you again.