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Advice for casting head/shoulders in latex

edited September 2016 in Fabrication
Hi. I'm working on a prop for a short film, which involves life-casting a head and torso. The finished piece will ideally be hollow rubber.. I'm thinking latex.. I don't have the facilities to make or bake foam latex. The cast head will be torn open down the front, with a puppet creature inside (not torn on screen, the prop itself is already torn) similar to in the concept drawing here. I'm having a hard time figuring out the best way to cast the head in latex though.. Can I cast latex by building up layers directly from into an alginate mold? Or would we need to use silicone for the mold? Any suggestions for building up some shape/strength in the latex would be helpful too, as I know that it will end up being fairly floppy. (in some places that will work, ie: where it's tearing open in the face.

Any help would be amazing.
Thanks so much.

Comments

  • Chris EllerbyChris Ellerby Los Angeles Admin
    Hi Seth,

    You can brush latex into a stone mold (plaster, Hydrocal, Ultracal, etc) pretty easily.  The moisture in an alginate mold would slow down the drying of the latex and may get a bit messy.

    To build up structure or add extra details you can use liquid latex with cotton and tissue paper much like paper mache.  

    You can embed armature wire, chicken, wire, or other semi rigid material on the inside of areas you want to prevent from flopping around too much, or you can fill in the voids with cotton batting or foam to add some structure.

    We have a lesson on life casting that may help you as well:
    https://www.stanwinstonschool.com/tutorials/how-to-life-cast-character-creation-tutorial

    /Chris
  • edited September 2016
    That's great! Really helpful, thanks Chris!
    I guess my main sticking point was if I made an alginate mold, what kind of positive would I need to then get to a stone mold? Can I do a hydrocal cast, then seal/vaseline it, and do a hydrocal neg mold from that? Or would it be better to cast something like a resin positive to then do a hydrocal negative/mold to get the latex positive?

    My other option.. I just spoke to a person from Smooth-On, and they suggested that I could also do a silicone cast/mold (like in your video.. which I've watched a few times.. super helpful!) and then cast it with Urecoat by doing it in layers like latex.. From what they said, I should be able to do Urecoat directly into a silicone mold, and it also doesn't shrink like latex does (or it might a tiny bit, but it's negligible.) They said the Urecoat is very flexible, and could be made fairly skin-like, but could also be build up in areas for strength/thickness. Does that sounds reasonable?

    Another advantage to that obvs is that with the silicone mold, I could also get a number of positives, including a hydrocal as a backup, or if we need to do any prosthetics.

    Thoughts? Does this sound like a decent option?
    Any benefits to using latex over a urethane rubber? Sounds like urethane has a few benefits that might make the process a bit quicker, and make the final thing a bit more durable, but I'd love to hear expert opinions.

    Thanks again for the help! This site is amazing!

  • Chris EllerbyChris Ellerby Los Angeles Admin
    Hi Seth,

    Since your goal would be a negative stone mold that you can dwell latex in, you'll want the cast copy of the head to be flexible so it can be removed from the rigid stone mold without locking.  Silicone would work, as would clay.

    One budget option would be to make a alginate mold of the mask and then pour melted clay (like Monster clay) into it.  Just make sure the temperature of the melted clay is below the boiling point of water (212°F or 100°C) so it does not react with the moisture in the alginate.  You could then make a stone mold of the clay positive.

    You can also pour clay into a silicone mold, which is more durable and can be used for other castings, but costs more.

    I've not used Urecoat, but a thin urethane rubber like that should work just fine. While it would be more expensive than latex, it would have a longer life span.  Latex (being an organic rubber) breaks down over time.  How fast depends on what protective coatings it has and exposure to UV light, heat/cold, oils, etc.

    The advice from SmoothOn is good, as long as you can afford it.  And any chance to familiarize yourself with there materials is always a good learning opportunity.  They make a lot of great stuff.

    /Chris

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