Bubbles in wax cast.

Discussion in 'Lost wax casting' started by LJLundgren, Jul 31, 2020.

  1. LJLundgren

    LJLundgren Copper

    Anyone have tips on how to reduce bubbles in a wax cast? Or how to clean a silicone rubber mold?
    I made a little mold of a trilobite I found out of silicon rubber. But it’s not casting as clean as I would like. I’m using micro crystalline wax but I couldn’t tell you what kind or any specifics other that I got it from a local sculptor. upload_2020-7-31_16-3-53.jpeg
    My mold looks like it needs to be cleaned.
  2. Zapins

    Zapins Silver

    I have this issue too I have not found a perfect solution to it.

    Some say wax temperature is important. I think the surface of the mold needs to be prepared in some way with an oil or something to break the surface tension as well as proper wax temperature.

    Are you using a silicon rubber mold?
  3. LJLundgren

    LJLundgren Copper

    Yeah it’s silicone rubber.
    do you find that high or low temps are better?
  4. Zapins

    Zapins Silver

    Lower are better but I have noticed that the first few wax copies made in a fresh mold have more bubbles. The longer you leave a mold the better the wax copy. The more you use a mold the worse the copies seem to get which is what makes me think there must be some kind of oil or some coating that leaches out of the rubber with time and improves surface finish and when gone seems to make the bubbles worse.

    Maybe a mold release compound would help? I have meant to experiment with it but every time I forget and then end up spending hours repairing bubbles by chasing the wax.
  5. Jason

    Jason Gold

    Even though you shouldn't need it. Trying moldease wouldn't hurt.

    Hey Lucas, are you first soaking your plaster mold in water for 10-15 minutes???? You need to do this first, pull out of the water, shake it off, dab with a paper towel and get to pouring the wax. Bubbles can come up from a plaster mold and screw your wax. This is one of the things that make plaster mold a PITA to use. I avoid them when I can, but some times, I just suck it up. ZAP is right, the more you use a plaster mold the more issues you can have.

    Zap remember the plaster mold to make sheets of wax you had me make? It was great for the first year.. After that, it's been bubble city. Time to make a new one. I prefer floating wax these days on screaming hot water.
  6. Zapins

    Zapins Silver

    Ya. The plaster molds work okish. I switched to using a glad bottom silicon rubber baking tray and pouring hot wax onto it then pouring it off. Building up about 3 layers of wax for thin wax sheets. I actually started using a paper cutter (the big ones they use in the old libraries) to slice the wax sheets into strips or stringers of wax that can be use for fine detailed work. Much easier to make that way than with the horse/lube syringe method...
  7. LJLundgren

    LJLundgren Copper

    So I took some hot water and carefully wiped out the mold the clean it, then sprayed some mold release on it and used a low temp wax. It came out way better!

    That’s good to know Jason, the only part of the molds I’ve been using that is plaster is the backing of the mold. But the mold itself have all been silicone rubber. I did get wax all over my plaster backing though and if I had soaked it like you are saying it would be a lot easier to get it off.

    Jason likes this.
  8. LJLundgren

    LJLundgren Copper

    It turned out pretty well!

    Attached Files:

    Jason, Zapins, Tobho Mott and 2 others like this.

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