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Dave Parvin

Joined: :
16-Mar-2005

Started On : 12-Jan-2013 at 12:03:22 PM, #Views : 1152

Topic Subject : Re: Jesmonite

Chris, either material will work just fine, I have used both in similar sized pieces numerous times. If you use polyurethane, I would suggest that specify rotocast resin which has a longer gel time allowing for a more uniform buildup in the mold. As you probably know, most polyurethanes transition from liquid to sold in just a few seconds. If you are rockin and turning the mold trying to keep a uniform layer on the inside surface of the mold, when the urethane kicks off, you will almost always get a big lump somewhere with regular resin. If designed for rotocasting, this problem is pretty much eliminated. Also, do not try to get the desired thickness in one layer. I would suggest several small layers. If you use metal powder such as copper or bronze, you will only need the powders in the first two layers. Also, a dusting of metal powder inside of the mold will be on the surface of the casting allowing for a more true metal look and more intense patination. Lastly, if you use urethane, do not use urethane rubber for the mold since urethane sticks to itself. Use silicone rubber and you will not even need a mold release since urethane and silicone do not bond together.
As for Jesmonite, called Forton MG in the States, in the AlI Library, I have a two articles titled "How to Cast a Head in the Round. In Part II, I explain in detail how I constructed the mold and then cast the head using Forton MG. The method I used should work just fine for your project.
As I said, I have used both materials MANY times. My preference would be for the Forton MG. If I can help you in any way, get back to me.
Dave

 
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