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  1. #21
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    Ok, ok, bossy...


    What is needed for this project:

    Skull Mold, or skull to make a mold out of.
    Mother mold for the mold.
    A clear casting resin. (more on that later)
    A well ventilated work area.

    First, obviously, is making the mold.

    Instead of rewriting a bunch of stuff I've already posted, I'll just direct you to my mold making tutorial here:

    http://halloweenforum.com/tutorials-...tml#post444665

    And highlight what we're doing different for the Crystal Skull.

    For the resin we'll be using, you want relatively shallow nose and eye cavities, and they should be filled in accordingly. I used Model Magic again, as in the tutorial above, but I have come to find the new Crayola Air Dry clay to be both better and cheaper. But, it needs to be allowed to dry, and sealed with a coat of a lacquer spray. Were I to start one today, that's what I would do.

    If you are using the Lindberg Skull, you will need to add some clay to the nose bone as it's too thin, or remove it and sculpt your own.

    We also need to fill in the gaps behind the teeth if you're keeping the lower jaw. I filled the entire jaw cavity with model magic.



    Now that the model is prepared, make your mold as listed in the tutorial above, however, we want to encompass the model fully, only leaving a small area to pour into. And, reinforce the ENTIRE MOLD with the cheese cloth. Top, bottom, undercuts, whatever. The resin we're using is heavy, and we need the reinforcement to keep it's shape.

    CUT a seem from the pour location as far back as you need to remove the mold.

    The use of the seem also will make things MUCH less easier and less of a mess than attempting to rely on the latex stretching when it comes to removing the mold, and it's best to reinforce the seem with the cloth to prevent ripping. Thus, the decision to cover the whole with cheese cloth.




    Now then, tape that seem back together. I crossed the seem with electrical tape, then ran the length of it with painters tape. But, were I doing this again, I'ld skip the painters tape and cover that seem with more of that air dry clay, let it dry, and duct tape it in place.



    The Mother Mold:

    A mother mold is just something to keep the mold itself in the proper shape.

    Some of those plaster bandages you can buy at michaels would be great. Some plaster itself would work. Anything. I used Model Magic because it's what I had, and I didn't want to get to the store.

    Just made a framework for the mold, broke it in 2 (so it could be removed later), and taped back together in redneck moldmaking glory.





    The Casting...

    I'm using Castin' Craft Polyester Clear Resin (AVOID the "easy cast"), which you can read more on here, because that is what Michaels had, and I had a bunch of 40% off coupons to use. Without the coupons, best price on it is available from Delvies Plastics. Delvie's Plastics Inc.: Casting Resin

    They also sale a bunch of tints, if you want a colored one.

    I'm tempted to suggest the 'surface curing agent', because this WILL come out sticky/slimy. But, I have no experience with it, and the now 2 dozen or so I've cast (most of them mini skulls my son sold, see mold making thread above) all the surfaces have hardened over time.

    IF BUYING FROM MICHAELS you need to ALSO purchase the Catalyst seperately. Delvies sends enough catalyst with each package of resin.

    THIS GIVES OFF A STRONG ODOR and poisonous fumes while curing. VENTILATE the area well.

    THE CATALYST WILL BURN you if its in skin contact long. Gloves, people. And I hate gloves. And, FYI, I had one bottle, new, that had some residue of the catalyst on it's lid. My fingers paid for lack of gloves a few hours later.

    CURING PRODUCES HEAT And lots of it. PLEASE allow the mold to COOL completely before attempting to remove. As mentioned above, the stuff will still be sticky, and sticky heat on your skin is not a good thing.

    Now come the questions:

    How much do you need? If using the Lindberg Skull as prepared above, just under 1 gallon. If not, fill your mold with water, and dump it into a measuring cup.

    To fill the mold completely and without gaps will require 2 seperate pours. One for the brain cavity, and one for the face, so mix 2/3 up, and pour it in, then tip the mold upright and allow to cure. Then tip it back and do the face.

    HOW MUCH CATALYST DO I NEED?!?!?!

    THIS is THE question. And...I don't have a definitive answer...since the instructions only list thicknesses up to 1 1/4"...and we are WELL beyond that. Further, we are doing a 3 dimensional mold, which the directions simply tell you to consult the mold maker.

    Too much catalyst, the polyester will crack under the heat. Too little and you get a gooey mess.

    Fortunately, there's a wide middle area where a little too much just turns it a bit yellowish, and a bit too little just makes it take longer to cure. And, as mentioned, I did 2 dozen smaller ones to get a feel for how this reacts with 3 dimensional molds.

    I'll edit up this spot with what I used when I get home and can be absolutely sure of the measurement, not post from memory. I do know I erred on the low side, as this particular skull took a few days to cure, and a week for the surface to fully cure after releasing from the mold.

    EDIT: I used for Skull 1: 2 drops per ounce, 16 drops per cup. And, yes, I mixed a cup at a time as it was all I was comfrotable being sure it would accurately get measured and thuroughly mixed. This was on the lower side, and each pour took a good 24 hours or more to harden up, but a part of that was due to the fact I did it in less than ideal temperatures. Patience is a virtue here. You could likely pump it to 20 drops per cup just fine, likely even more if you are pouring at a consistant room temperature.

    Skull 2 is a whole other ballgame as it's mold required 5 seperate pours of much smaller volume. I'll get it's picture up soon.

    Skull
    Hopefully Skull 2 is a bit closer to the proper #. (should finish it tonight)
    Last edited by UnOrthodOx; 06-12-2008 at 04:59 AM.
    www.AnUnorthodoxHalloween.com

    I figured out why you call yourself that - you spark unorthodox thoughts and ideas in others. - Hallomarine

  2. #22
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    Apr 2008
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    Macomb, MI
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    Just a word of caution - if you over catalyze polyester resin it can catch on fire. Also, polyester resin is very brittle and can shatter if dropped. If you are going to convert these into animated skulls, you might want to use a 2 part urethane resin. They make high strength resins (such as Task 2 by Smooth-On - I use this to make prop helmets) that would probably work well for this application.

    Randy
    No matter where you go , there you are...
    http://www.evil-land.com

  3. #23
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    There are other products to make this, to be sure.

    Clear Urethane resin is a fair bit more expensive (roughly double), would likely be best in a silicone mold, is touchy to moisture and humidity (discolors the clear), and requires the ability to accurately measure and mix the 2 parts at the proper temperatures. The cost alone turned me away from these.

    Epoxy resin being the other I know of. Again, it was more expensive, but not much, and in my experience is VERY touchy to both temperature and accuracy of mixtures (often not simple 1:1). Ruined one of the smaller skull molds exploring this as the stuff never set up, another came out more a frosted glass look, a third was nice and clear. Which was aweful confusing to me as I measured and mixed all 3 at the same time.

    (I'm not even counting any products requiring hot pours)
    www.AnUnorthodoxHalloween.com

    I figured out why you call yourself that - you spark unorthodox thoughts and ideas in others. - Hallomarine

  4. #24
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    Jun 2008
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    Milford CT
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    Very cool! Great tutorial. I'll give it a shot once the weather evens out up here. I'm definately not going to do it in my house.

  5. #25
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    Apr 2008
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    Sorry, forgot you want it to be clear. Clear urethane resin is tricky and expensive. You don't necessarily need a silicone mold as long as you use the correct release agent.
    No matter where you go , there you are...
    http://www.evil-land.com

  6. #26
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    Editted in the amount of catalyst used. Just had to be sure my memory was right before posting it.
    www.AnUnorthodoxHalloween.com

    I figured out why you call yourself that - you spark unorthodox thoughts and ideas in others. - Hallomarine

  7. #27
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    Jun 2007
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    VA
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    UnOrthodOx, those are BEAUTIFUL!!! I love the leds in them, very cool. You certainly are a talented prop maker.

    Draco dormiens nunquam titillandus

  8. #28
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    May 2008
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    So (Scary) Ca
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    Very Cool looking!!!
    Please check my 2013 Haunt album in Photobucket. http://s127.photobucket.com/user/Lon...lloween%202013
    Thanks
    Comments/explanations added 11/07 ALSO, see my Halloween Forum Albums

  9. #29
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    Sep 2007
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    Sevierville, Tenn.
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    ok those do really look great.
    Keep us posted to the animation of a crystal skull too ... please.

  10. #30
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    I don't think these would do well for animation.

    They weigh a fair amount, and you'ld burn up your servos pretty quick.

    You'ld need a hollow casting to get it light enough, and to have space for all the items to animate it. (which would be seen) That would require some other equipment just to get the casting, I believe.
    www.AnUnorthodoxHalloween.com

    I figured out why you call yourself that - you spark unorthodox thoughts and ideas in others. - Hallomarine

 

 
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