Casting pewter in RTV Silicone

I want to reproduce a bit of jewellery I have designed in pewter by using a 2-part RTV silicone mould.

By all accounts it is possible but I've run into some problems when sourcing materials.

Most high temperature silicones I have come across state a maximum temperature of 250°C, But pewter has a melting point of around 280°C.

My feeling is that the mould itself will most likely never actually reach 280°C and will probably only be above 250°C for a short period of time.

But I'm wondering if anyone has actually done this and could verify for me. Also as I'm new to the whole process, any other tips are welcomed.

This is the high temp silicone I'm currently looking at.

Thanks,
               -Tom

rachel5 years ago
Did you ever try this? What were your results?  I have a project I think would work well in cast pewter but I have not tried it yet.

A couple years ago I did some experimenting with bismuth, which has a melting point of about 270 C. I poured the melt into silicone molds (see here).  The silicone held up totally fine.  I don't know exactly what temperature the molten bismuth was at, but it was obviously at least that!

madmanmoe64 (author)  rachel5 years ago
I've tried casting with some really good results. The only problem I've had is getting the pewter to fill the very small areas, so make sure you don't have any details smaller than 1mm.

Also I found that using a two part mould gave me much better results (less pitting, shiner surface, better detail) than a 1 part mould.

I've actually refined my technique quite a bit so if you want me to give you more detail on what I was doing or just show you some pictures, then let me know.
Honus6 years ago
Smooth On makes a silicone RTV that is specifically designed for this purpose. It costs about $24 for a small casting kit.

http://www.smooth-on.com/gallery.php?galleryid=424
caitlinsdad6 years ago
I guess the best thing is to try it yourself. Worse is that you will be out a coupla bucks for a tube of goo. Maybe freeze or refrigerate the mould before the pour but I don't know what effect thermal shock has on the pewter. Good luck.