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  1. #1
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    Best material for long work time, large size, master for epoxy resin mold

    Hi all,

    I'm totally new to all of this, so please forgive my ignorance.

    I'm working on a project to create a sculpture 30" high (and about as wide and deep). The master can be made of anything I like, but must be compatible with epxoy resin that will be used to make the mold from the master.

    Because of the size, I am using metal rabbit fencing as a structure to support the modeling material (and to check my proportions before I get too involved). Also because of the size, I am concerned about finding a kiln that can fire it.

    I need to be able to sand and polish the master to a near-mirror finish for the molding process, then apply a release agent and epoxy resin & fiberglass mat to make the mold.

    So - any suggestions on a good material to use? Is there anything that air dries to a hard enough surface to be sanded and polished? (Something that has a long working time, as long as it is kept moist)?

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  3. #2
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    Talking Updated question

    OK, I've done some more research, and I THINK I have a process, but I need your feedback, and I have some questions:

    I am considering using Sculpey to create the model, then sanding, painting, sanding and buffing it to a mirror finish. I will then use latex rubber to make a mold, with fiberglass as the outer shell of the mold.

    Using the mold, I plan to create copies of the original in epoxy resin and fiberglass mat, and eventually in polystyrene resin and fiberglass mat.

    I would greatly appreciate your help with these questions:

    1) Am I going down the right track? Will this process work?
    2) Can you recommend any good sealer that I can apply to the sculpey, then wet sand and buff to a mirror finish? Or is there something that I can apply directly to the sculpey, then apply another coat to sand and buff? Could I use epoxy resin for this purpose, since it will give me the depth and the hardness I need to create the mirror finish?
    3) Do you have any suggestions for the rubber to use? I would just go with a straight epoxy fiberglass mold, but I am concerned that with the complexity of the model, and my inexperience with fiberglass, that I might have difficulty getting the first few parts out.

    Please help,
    William Farrell ("Nowandever29")

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  4. #3
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    I would not suggest working in sculpy on that scale as it is HUGE and EXPENSIVE! I would suggest working in something like plasticine clay, its an oil based clay that never dries or hardens so you dont need to worry about it hardening up on you.

    Then you can take a mixture of shellac and alcohol and seal the clay so it is non pourus. Then you put a thin coat of butchers wax on there to act as a release agent.

    Then you can use the rubber and fiberglass to make the mold as you were going to.

    I would suggest you goto www.polytek.com and do a little more research before you go and undertake a project this big and in reality expensive.

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    How does oil-based harden? How do I get finish?

    Thanks! I really do want to avoid wasted time and effort, I know that there are people who have done this before, so why not learn from others?

    Regarding your suggestion, I am willing to deal with the expense of sculpy if I get ease of use and effectiveness in return. I am quite new to this process, so ease of use is critical.

    That being said, if I follow your advice (and thank you for it!), how does an oil-based clay harden? If it doesn't, I'm worried that at this size, the weight of the rubber and fiberglass may deform the master while I am making the mold. And would the shellac and alcohol provide a hard surface that I can sand and buff to a mirror finish?

    Again, thanks for your help, and I'm looking forward to your answers.

    - Bill Farrell ("nowandever29")

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    There is a better approach than what you are considering. A couple of questions though:
    What is the content of the sculpt, is it highly detailed or simpler geometric planes or curves
    You mentioned making an epoxy mold, but then a latex mold and casting epoxy resin, what do you need the final castings for, outside or inside for example, and what finish are you putting on them, for example are you looking to put a faux metal patina, is that why you need the high polish finish.
    Give me a little more info, Ill let you know which way to go.

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    Hey Stine Sculpture:

    What I'm going for is a fairly large piece, with relatively large feature sizes (none below 3/8", I'd say). The biggest concern I have is that I be able to make the sculpey as smooth as humanly possible, because the finished product will be painted and buffed to a high gloss.

    As far as the sculpture itself, it's hard to describe (I'm very visual), I guess the closest thing would be to imagine making a house 30" tall and wide and almost as deep, with a chimney, a window jutting out from the roof (not sure what that's called).

    The final pieces will be epoxy fiberglass, again, with a smooth, paintable, gloss(able) finish.

    If you imagine demolding a house like this, you can see that it would take a ridiculously multi-part mold if the mold is rigid).

    So any advice would be great!

    Thanks,
    Bill Farrell, nowandever29

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    Hey Stine Sculpture:

    What I'm going for is a fairly large piece, with relatively large feature sizes (none below 3/8", I'd say). The biggest concern I have is that I be able to make the sculpey as smooth as humanly possible, because the finished product will be painted and buffed to a high gloss.

    As far as the sculpture itself, it's hard to describe (I'm very visual), I guess the closest thing would be to imagine making a house 30" tall and wide and almost as deep, with a chimney, a window jutting out from the roof (not sure what that's called).

    The final pieces will be epoxy fiberglass, again, with a smooth, paintable, gloss(able) finish.

    If you imagine demolding a house like this, you can see that it would take a ridiculously multi-part mold if the mold is rigid).

    So any advice would be great!

    Thanks,
    Bill Farrell, nowandever29

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    Hey Bill
    Your problem is going to lay in trying to find a material that you can sculpt in and also get a polished finish. There is really nothing out there that you can use on this scale without a tremendous amount of time and effort and elbow grease to obtain that kind of finish.
    What I suggest you do, is two molds. Do your original in a plasticine or some other realativly inexpensive clay that you can work in large scale with. Then make your first mold and cast a wax and finish that for your finish mold.
    Start with clay, get your forms as smooth as possible in that clay. Thats why I was asking what the finished imagery is, it sounds like you will have some nice large planes that you can smooth nicely.
    Make a mold on that using whatever molding rubber is compatable with your clay. If the piece is as large as 30" by 30", you still need to make a multiple piece mold because next you have to cast a wax into the mold, and the wax needs to be cast into the mold as a hollow piece. In a smaller mold, you could just fill it up, and then rotate the mold by hand to slush all of the inside walls to get an even thickness of material, but on this scale, of course you cant do that.
    Instead, what you will have to do is paint the wax onto each piece of the mold in an even thickness, trim and put the mold together, then slush the inside seam areas. If at all possible, get in touch with a lost wax bronze casting foundry, and see if you can observe there wax casting methods. What I am describing is how they cast large wax forms.
    The reason I am suggesting wax, is because it is a rigid, handleable material that can also be somewhat easily brought to a clean, polished finish. There are waxes out there that are inexpensive and easy to work with, they can be melted in a simple crock pot used for cooking!
    When your wax is finished, then you make your final mold on that piece.
    Now, this is all a very simple, concise description of a pretty involved process, but definately doable. You will need to do your homework and you will need alot of information on material suppliers, handeling of specific materials and there applications, moldmaking and casting techniques, etc. There are alot of sources available with all of this info. Polytek is one of them, people on this site are another.
    This, although it sounds involved, is the best approach. In the log run, it will save you time, energy and money.
    If you want to go this way, let me know, I can give you the details of the process and where to look for the information you will need. Good luck, Liz.

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