What type of clay to use for mold making.

[Blindhorizon]

I'm looking for a good clay to use for two part mold making, playdoh separates from the part leaving small gaps far to often. Any thoughts on this would be helpful.

Thanks,
Blind-

[Fleafa]

Plasticine does the job.

[mangozac]

Blind I can't believe you're still using Play Doh! Go and get some sulfur-free oil based clay. Art supply shops should carry it, but it's unlikely to be one of those multicoloured packs for $2. It'll be a big block of a single colour. Look for a nice neutral tone like grey or tan.

[Blindhorizon]

I'm doing a commission for a customer but since it was so cold here during winter and i can't cast as the resin sets brittle i hadn't had to update my casting technique. Now that it's warm i'm looking into alternatives. I got some craft smart plastalina modeling clay today though.

[mangozac]

You really should find out if that brand of clay contains sulphur, especially if you're planning to use it with addition cure silicone. A quick Google didn't turn up anything conclusive so either check the packaging or ask the place you bought it from

[Blindhorizon]

So how bad is sulphur for silicone?

[Blindhorizon]

it says non-toxic, is sulphur toxic?

[Blindhorizon]

Man now i don't want to use this stuff, are their any tell tales that will let me know if it has sulfur? I found a thread that said it will smell like rotten eggs but that is the only one and i'm hesitant to trust that.

Blind-

[mangozac]

You won't be able to smell it. If you're using addition (platinum) cure silicone the sulphur will prevent it from curing. If it doesn't specifically say on the packet then it's hard to tell. Non toxic does not mean no sulphur. Go back to the art store and ask them. If they can't answer then buy some sulphur free stuff instead.

[Blindhorizon]

Okay the art store isn't sure, i called their hotline and am having emailed over the MSDS which she told me stands for manufacture satfy data sheet. If that doesn't have an ingredients list i'ma get new stuff.

Blind-

[johncast]

Interesting post here, so I thought I add a bit to this interesting area of mould making.

Forming up the items for the first part of a 2 part mould , I find myself doing this 95% of the time to make resin and wax injection moulds. To get the results I want.
I guess I have been lucky but the average and cheap modelling clay I bought in the local newsagency works great. No mention of sulphur in the material but having used this for 80 or more moulds I don't have problems only that it takes a bit of work to remove once the first half is set. If the temperature is cooler the clay comes away a bit easier from the rubber.

Be advised that this could be a very different story with other rubber materials besides the rubbers I am using, which are the Barn's 4601 pink for resin moulds and for the wax moulds I use Slastic J 4130. from Era polymers and barns 4670 white..
The brand is Belgrave modelling clay and is a good pale grey. Item 1313 the label says
Quill stationary Park Road Regents park NSW 2143 Australia.
Made in Mexico

The biggest problem I have had is not washing the patterns before moulding, ESPECIALY RAPIDPROTOTYPE computer patterns. Gently with fine soft brush in warm water and dish wash liquid always ,,always wash the parts..before moulding. Hope this helps

Johncast