Metal Casting Zone

Hi Guys, i did try and post this already as you will see but the thread apepars to be faulty.

ive tried making a 2 part mould for my first cast and thought i would share my non succesfull attempt with you in an attempt to help myself and others!

ok, i made my master out of regular modelling clay, room temp drying, nylon re-inforced. the master was a belt buckle design but after some problems with the bits on the back i just ended up leaving it a dished celtic plate so i could get on with it and try casting.


next i got a wooden frame and i used kids plasticine to fill it half way up and sink the master into it half way i dont think plasticine is great htough as its too hard!


i then added the locations pins and the funnel part for pouring using more plasticine.


the next step was pouring my silicone (High temp RTV silicone, which is mixed 100 parts silicone to 1 part catalyst, making it tricky to measure and mix!)


The is where my problems began, the frame which i couldnt take apart meant getting the rather hard plasticine out was rather difficult!


As you can see the plastcine seemed to stick to the silicone and my clay master ended up breaking trying to get it out...


So.. next time im going to use a frame i can take apart, and i will use wooden dowels for the location pin holes so i can remove them after the first pour easier.

what id like to know though is:
1) whats the best clay type to use for a master, i liked the softness of modelling vlay and how i could let it half dry and them finish it when it was almost hard, but its too brittle, the nylon re-infocement makes a hairyness when you try and finish it once dry and it is quite powdery once finished also.

2) whats better than plasticine to fill the frame half way for the first pour? plastcine was really hard to get flat and push the master into.

That non-hardening clay can be real sticky. But, I don't know why the Silicone stuck to the pattern. Maybe you can seal the clay with a light spray of paint or varnish. Just test it to make sure it's compatible with the silicone. I didn't, and ended up with a gooey mess, the silicone reacted with the polyurethane spray I put on. I also used Sculpey polymer clay and Beeswax for the pattern.
Yes, I think making it so you can remove the frame will help. You can then bend the Silicone away from the pattern, stretching it a little, and it will usually let go.

I often use plain old modeling clay (non hardening) that kids play with.

Warm it in your hands and it works great for setting parting lines.

I also use tinture of green soap as a release for pouring plaster on a painted or plaster pattern. Most drug stores have it or can order it.

You can brush it on and then lightly wipe it with a soft cloth.

For pouring silicone,it should work as well.