Heating plasticine for silicone molds

I have often wondered if it is possible to heat plasticine clay to a very soft or even pourable consistency when making 2 part RTV molds. The way I typically do it (as most people do) is to embed the object to be molded in plasticine, pour the RTV over, flip it over once cured, remove the plasticine, apply mold release, pour the second half of the RTV, etc...

But the process of embedding the object in plasticine is often tedious and I was wondering if it is possible to heat the clay in, say, a double boiler and pour it around the object, and save myself the trouble of breaking off small pieces of plasticine, softening it in my hands, and working it all into the base of my mold box.

Does that make sense? Does anyone have experience heating up plasticine for the aforementioned purpose?

I personally HATE, DESPISE, LOATHE cleaning clay off the finished piece prior to molding the 2nd half and thus avoid it at all cost... Heating it up and letting it set against the part would only enrage me more

See this post for how I get a straight crisp parting line with minimal to no clean up of the part being molded

http://www.therpf.com/f9/getting-even-seams-two-part-mold-98557/

Try using Alginate. Float the item to be molded on some clay or plasticine pillars then pour the Alginate up to your part line. Give it thirty minutes to set then push in some Lego blocks to act as keys and pour the Silicone. when set turn the mold box over take out the Alginate and lego blocks and add mold release and more silicone. when dry this will make a great part line. Just make sure you remove the small round bits on the silicone lego keys otherwise it makes it hard to get back together again.

exoray said:

I personally HATE, DESPISE, LOATHE cleaning clay off the finished piece prior to molding the 2nd half and thus avoid it at all cost... Heating it up and letting it set against the part would only enrage me more

See this post for how I get a straight crisp parting line with minimal to no clean up of the part beyond molded

http://www.therpf.com/f9/getting-even-seams-two-part-mold-98557/

Click to expand...

SUPERB!!
Thank you exoray thumbsup:thumbsup This will be an ideal solution for moulding Bob.
My worrie was using oil clay for partitions upto an oil clay sculpture & leaving a mark in the sculpture after the partition's removed. This method will work a treat Thanks again

Here is a video of the process. Mold Making with Silicone: 2 piece mold with alginate parting line - YouTube

Thanks for the response. There's some great ideas here that I'll definitely use.

The one thing is that they are mostly for straight and level part lines. What I like about plasticine is that it can be shaped into irregular part lines. Though I do agree with exoray that removing the plasticine is a pain in the butt and totally embedding something in it, unless it's a relatively simple shape, isn't practical.

I'm curious if it would be possible to submerge half of the object in something like sand, then pour a thin layer of plasticine over it, and then add on extra plasticine in areas where the part line needs to be elevated or irregular.

The question remains, has anyone ever heated plasticine clay into a pourable consistency? I may just have to try it myself and see what happens.

Mr. Nagata said:

The question remains, has anyone ever heated plasticine clay into a pourable consistency? I may just have to try it myself and see what happens.

Click to expand...

Yes, I have... Different clays will result in different consistencies and remember it's HOT, STICKY and HOT! But, once you get it melted it's just like syrup or a thick goo, and it's generally thin enough to pour just fine... Caution should be taken though as the temperature might very well harm the original piece being cast... BTW I highly suggest using a hot plate outside to do the heating, it stinks!

I'm curious if it would be possible to submerge half of the object in something like sand, then pour a thin layer of plasticine over it, and then add on extra plasticine in areas where the part line needs to be elevated or irregular.

Click to expand...

If I need to use clay I will generally lay down a bed of soft clay, and then cover that bed of clay with that stretch to fit plastic wrap, or even regular plastic wrap... Then work the piece into the covered bed of clay, this way no clay is in contact with the piece... I will then use a thin coat of clay over the entire plastic wrapped clay bed to make the final edges to the piece and also seal the bed for the silicone... Don't just do a partial layer of clay as it won't always seal to the plastic wrap and you will get silicone oozing into the seam, apply a complete layer over the plastic to avoid this...

exoray said:

I personally HATE, DESPISE, LOATHE cleaning clay off the finished piece prior to molding the 2nd half and thus avoid it at all cost... Heating it up and letting it set against the part would only enrage me more

See this post for how I get a straight crisp parting line with minimal to no clean up of the part being molded

http://www.therpf.com/f9/getting-even-seams-two-part-mold-98557/

Click to expand...

This is brilliant. I remember reading this but it didn't sink in till just now.

Rebelscum said:

This is brilliant. I remember reading this but it didn't sink in till just now.

Click to expand...

Yeah, I want to do a little video or at least some pictures to make it more clear, just too busy with everything else right now...