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Mold Making and Resin Casting

For simplicities sake, we will use a 1/1 ratio RTV (Room Temperature Vulcanizing) Silicone (Fig 4). Although this type is more expensive by volume than it's 10 to 1 cousin, it is far easier to use and you are less likely to make a mistake with it. The 10 to 1 mix requires a digital scale and has a 24-hour set time. The type we will use here sets in 4 hours. You can start making parts after the set time expires!

Here is a tip that will help you in knowing how much silicone to mix without getting into complex math problems or guessing.
mixing tipWith your part(s) in the mold box, pour enough water into the box to cover the parts being molded by about a half an inch. Pour this amount of water back into an empty mixing cup. Now, in another cup of the same volume, pour half of this water into it until both cups have an even amount in them. This is the amount of each part of your Silicone you will need. Easy huh? In other words, volume of water in mold box equals total volume of silicone for mold. Mark a line on each cup at the water level and empty the water and dry them out really good. Do the same with your mold box. Use a hairdryer to make sure that it is completely dry. This is important.

Now, using the cups that we marked earlier, pour an equal amount of parts A and B silicone into each cup, right up to your marked line (Fig 5). The silicone we are using has one white part (A) and one blue part (B) and when mixed will by a light powder blue in color.

In your separate clean mixing bowl, pour both of these in. Make sure you scrape the sides of the cups really good to get all of the mix. Use your spatula to mix these together in the bowl really well. You want to mix, not whip these as whipping causes air bubbles to form in your silicone.

Scrape the sides repeatedly during this process. When it is thoroughly mixed, you will not see any white streaks (Fig 6).

We are now ready to pour.
  • fig4
  • fig5
  • fig6

About the Author

About Steve Sherman (bowjunkie35)

Steve is a freelance propmaker (the movie kind) and machinist. A former construction worker, he has been working with tools since childhood. He learned the construction/ metal fabrication business from his Father, so to follow in Dads footsteps was natural. Since leaving the construction industry, h...


Good informative article, very interesting. I've often considered making my own castings but have been deterred by the cost and lack of advice- at least one of those hurdles has now been addressed!
JAN 03, 2005 - 07:24 AM
Informative article, thanks, now maybe I can get rid of those lousy rubber/vinyl tires...... :-) :-) :-) :-)
JAN 03, 2005 - 08:23 AM
Yep, that is what I do also. It's in the article! Thanks Again guys for the compliments. LogansDad, I also use the 10:1 ratio RTV as it is more economical but much harder to use especially for someone just starting out. I used the 1:1 ratio RTV for the artivle for simplicities sake.
JAN 03, 2005 - 08:24 AM
Great article, Steve. I recently made my first attempts at molds and casting, and it seems like fun. Your info will help a lot. Thanks for all your hard work!
JAN 03, 2005 - 01:21 PM
I was trying to use the micro - mark info but it wasn't as awsome as yours. Now I might be able to do some stuff without ruining it., or waste money to just buy one part from a figure set. Thanks for the info. Happy Modeling
JAN 03, 2005 - 04:34 PM
Well thanks a million for sharing all these nice info with us . U really capture the whole procedure in a very good way amd very simpe to follow. Now i just have to come over there and get all the materials , rubber silicone and resin ...... Super nice article Costas
JAN 03, 2005 - 08:04 PM
hi Steve, thanks so much for the great article and very good photos. I felt reading a chapter of a modelling book more than a feature.it was very very helpful. congrats
JAN 03, 2005 - 11:40 PM
Just in time. I'm actually casting a couple of alice packs and German ww2 bergens.
JAN 05, 2005 - 01:25 AM
Wow!! You all are far too kind! It was really my pleasure, but the positive feedback is great. I am getting misty eyed! *tear* :-) :-) Again, Thanks for the comments, they do not go un-noticed!
JAN 05, 2005 - 03:43 AM
it's been said,but still...great info, very well presented, nice tone, am excoted about casting! Thank You!
APR 03, 2008 - 11:28 PM