Help for a newbie


I'm completely new to special effects and character design. I'm a little confused about undercuts. I know they're bad, but am not entirely clear what constitutes as an undercut and how to get around them.

I'm making a latex mask for halloween. I sculpted a muzzle and ears to cast separately. I'm including pictures of the muzzle. In order to make a mold of this, how many pieces should I do and where should I put the clay walls to keep from undercutting?

Any advice would be greatly appreciated.


  • Undercuts are primarily a concern when you are casting rigid objects, or molds with a rigid core.  They can also cause wear and tear on the mold or your cast pieces over time.

    In the case of your muzzle, you will likely want to cast a flexible material like latex, so it should be easy to pull out of a rigid mold.

    Undercuts are just a part of your sculpted form that would prevent pulling your clay (or what ever you cast in the finished mold) out of the mold.    This image might help you visualize that:

    Where undercuts are depends on how you mold your piece.   Where parting lines are, how many pieces the mold consists of, etc.

    Normally a muzzle appliance like what you are working on would be sculpted on a head form or life cast.   Part of that head form/life cast would be duplicated and used as part of your mold

    One good place to learn about how to mold a piece like this would be Rob Burman's two part "Prosthetic Makeup Basics" lesson series:
    If you are in a hurry, one option would be just do a basic one piece stone mold with the snout facing down, leaving the base of the appliance (the part that meets your face) as exposed clay in the mold.   Then you could brush latex into the mold in layers to create the appliance, brushing less latex where the blending edge would be to keep it thinner.

    Here is across section of how you might do that as a one piece mold.  Note that the mold is extend up beyond where your appliance meets the face in this design.  This is to allow surface to brush on your blending edge.  To get this shape in the mold you would extend your clay sculpt to fill that space.

    That design would have a couple undercuts, one minor one for the right side of the nose in this picture, and a more severe undercut where the nose and muzzle meet (highlighted below).  But if you are casting a flexible material like latex you should be safe.

    This type of one piece mold will not give you the best blending edges, but if you want to get this quickly done before Halloween it might be your fastest/easiest option.

    As your appliance would not have the best blending edges, you would want to use something like bondo (slang term, not the automotive filler), aka cabo patch, aka thickened pros-aide to help blend that edge into your skin.

    Best of luck, and I hope you can share your finished character with us here!

  • Chris,

    Thank you so much for your detailed and thoughtful advice. I was able to make the mold!

    This isn't finished yet (still have to attach bottom jaw/muzzle), but I'm getting there! I'll post the finished piece sometime tomorrow.

    It's definitely been a learning process, but for my first time...I'm happy!

  • Awesome, it's looking great!  Glad you were able to get everything molded and cast.

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