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  #1  
Old 06-17-2009, 12:35 PM
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apprentice apprentice is offline
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Last Minute Mold Making Question/Alternative Material

I have a plastilene bas relief that I just finished and I'd like to add it to a show this weekend.

Unfortunately I am out of rubber and there is no time to order more...

Is there anything I can find at a hardware store or Walmart that would make a quick flexible mold to get one or two plaster castings? For some reason I'm almost sure someone mentioned plumber's putty. Anyone know for sure and/or whether it works? Other suggestions?

Thanks!
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  #2  
Old 06-17-2009, 12:42 PM
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mantrid mantrid is offline
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Re: Last Minute Mold Making Question/Alternative Material

Quote:
Originally Posted by apprentice View Post
I have a plastilene bas relief that I just finished and I'd like to add it to a show this weekend.

Unfortunately I am out of rubber and there is no time to order more...

Is there anything I can find at a hardware store or Walmart that would make a quick flexible mold to get one or two plaster castings? For some reason I'm almost sure someone mentioned plumber's putty. Anyone know for sure and/or whether it works? Other suggestions?

Thanks!
Silicone Bath sealer. Relatively cheap, and is in paste form that you can spread over your bas relief. It does tend to shrink after a few months but this shouldnt bother you as you just want to produce something quick. It air cures quite slowly forming a skin first (or at least the brand I used did), so you may want to put it on in a few layers. You could also use that aquarium sealant, this cures more evenly and quickly but is more expensive. it is also transparent which could be useful.
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  #3  
Old 06-17-2009, 12:45 PM
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apprentice apprentice is offline
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Re: Last Minute Mold Making Question/Alternative Material

Thanks for such a quick response. This site always comes in handy in times of need.

What is the approx. curing time for the bath sealer? Does it take to detail okay?
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  #4  
Old 06-17-2009, 12:59 PM
grommet grommet is offline
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Re: Last Minute Mold Making Question/Alternative Material

Quote:
http://www.instructables.com/id/Mold-Making-with-Jello/

"I just came across a couple of books with interesting information on making gelatin molds and agar moulage molds.

Turns out gelatin is better than I thought, and used to be common for low-volume casting (up to a few dozen things, I think.) Very interestingly, it IS reusable---you can melt it down and use it to make another mold 5 to 15 times. Cool.

(It's not as reusable as agar moulage, which you can use 50 to 100 times.)

To make a gelatin mold more durable, you can swab the surface with a solution of alum and water. That will make it tougher and more heat resistant. (1/4 pound powdered alum to 1 pint hot water). You can then apply a mold release that's just stearic acid in kerosene. (melt 1/4 pound stearic acid and mix it with 1 pint kerosene.)

To make the molds last a lot longer, you can use mostly glycerin or propylene glycol rather than water when cooking up the gelatin. It will dry much, much more slowly and you can get a bunch of casts out of it over several days.

For details, check out "How to Make Professional Molds and Castings, from Plaster to Plastics" by Ralph Travers. (If your library doesn't have it, they can get it by interlibrary loan; that's what I did.)

For agar moulage recipes and instructions, check out "The Materials and Methods of Sculpture by Jack C. Rich. I did some research, and the best place to get agar agar powder is usually from a local asian grocery store. Most of them sell "Telephone" brand agar agar in .85 oz. packets, and it's good stuff.

The big advantage of agar agar is for lifecasting. It has a low melting point and an even lower re-solidifying point. (It has "hysteresis," meaning it doesn't like to change state, so you can let it cool well below its melting point before it will go ahead and re-solidify. For life casting, that means you can let it cool almost to body temperature before putting it on somebody.

For non-lifecasting, gelatin is likely better. I think it's tougher, and easier to apply, and its higher melting point means that you can cast things in it that get pretty warm when they set. (But not really hot.)"
the silicone I think is at least a 24 hour thing. depends on the relief too. I was molding bark, so it had a lot of depth & took a couple days.
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  #5  
Old 06-17-2009, 03:07 PM
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mantrid mantrid is offline
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Re: Last Minute Mold Making Question/Alternative Material

Quote:
Originally Posted by apprentice View Post
Thanks for such a quick response. This site always comes in handy in times of need.

What is the approx. curing time for the bath sealer? Does it take to detail okay?
As mentioned 24hrs sounds about right. Also it will say on the tube. It takes detail very well and is very firm when cured, but as it doesnt flow you must be careful to brush it into all the recesses well.
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  #6  
Old 06-17-2009, 04:30 PM
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Re: Last Minute Mold Making Question/Alternative Material

Thanks a million for both of your help.

I just found some polytek rubber in my basement that looks good as new. I'm in business!
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  #7  
Old 06-17-2009, 04:33 PM
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GlennT GlennT is offline
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Re: Last Minute Mold Making Question/Alternative Material

Unless you have severe undercuts, a bas-relief can be cast in plaster from a plaster mold, more than once, if you do things right. With undercuts, you could fill them with clay on the original, take the plaster mold, and then carve the plaster cast to restore the undercut areas.

To get a plaster cast to seperate from a plaster mold, you first take the dry mold and go over every surface with a clear blue or green liquid dishwashing soap, or some equivalent. After that has soaked in and there is no wet areas of residue, you then go over every surface with a very light coat of vaseline, using fingers to get it as thinly applied as possible, and taking a light touch with a paper towel to sweep out any areas of pooled vaseline.

Depending on the mold, once the cast has dried, you pry it out slowly and carefully using a very thin metal device, going bit by bit around the edges so as to equalize the prying pressure, and also soaking it with water or adding water in the edges that will seep into the whole surface between cast and mold to help in the separation.

Oops, by the time I wrote all of that you posted the finding of some more rubber. But you can save this info for another time.
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  #8  
Old 06-17-2009, 09:36 PM
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Lady Fingers Lady Fingers is offline
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Re: Last Minute Mold Making Question/Alternative Material

A tip for using the bath or aquarium silicone: make a little mix of half dishwashing liquid / half water, use this to wet your fingers or tools, pat almost dry...it will prevent the silicone sticking to everything. Turns a frustrating job into a pleasure x
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