[jmr1068204]

I have these large diamond shaped plastic paperweights with these big 3" medals in them that I basically want to remove the medals from (as I collect them and I'm into numismatics as a hobby). These medals were apparently placed in them when they were in liquid form in a mold. However, I'm also a little puzzled how they made them stay put if it was all liquid. There is no air space between the medal and the plastic. They are directly in contact with one another. On the flat bottom (closest) side, they are about 1" from the surface. All of them are that exact amount from the surface, so they couldn't have just been randomly dropped in. Yet there is no open space inside. They are not stuck to the plastic per se...I had a damaged one that I basically drilled out the plastic on and eventually got out, but I damaged that one a little getting it out. It is an odd thing to want to do, yes. This plastic is incredibly hard and strong. It doesn't simply shatter like most would, if say...hit with a sledgehammer or something. It will not "split at the middle"...it is one solid formed piece.

Any ideas on what type of (common and safe) chemical I could use to melt this plastic off, but yet avoid damaging or tarnishing the medal inside?

http://img607.imageshack.us/img607/8289/img3497n.jpg
 

[curiouscat]

Don't know if that's a thermoset or thermoplastic but what about trying to heat the thingies again and see if the plastic will melt or at least soften to the point that you could squash away the gooey mess.

Amongst solvents I'd try acetone to start with. That strategy would be to "dissolve" it away instead of melting it. Won't work for thermosets though; they'll just swell.  Others to try would be: MEK, MIBK, Toluene, Xylene, Methyl Acetate. Oftentimes a compatible cocktail might work better than any single solvent.

I've heard of a solvent called "Hexafluoroisopropanol" that will dissolve a lot of otherwise hard-to-dissolve polymers; but no first-hand experience with it. Might be a bit iffy to handle with its corrosive nature.

This plastic is incredibly hard and strong. It doesn't simply shatter like most would, if say...hit with a sledgehammer or something.

One trick is to cool it down and see if it becomes brittle; some do. If you have access to Liq. N2 it's worth a shot. Careful though. Don't want to make the medal shatter too. 

However, I'm also a little puzzled how they made them stay put if it was all liquid.

Maybe they molded the bottom half and when it got solid enough placed the medal on it (in a sort of cavity) and then poured in the rest?

[jmr1068204]

Thanks for the replies. A friend told me that they used to make something like this in plastics class at a school. They said it is made of polyester resin. They said a band saw might work, but I don't have anything like that. Any ideas with it being a poly resin? Would acetone work on it? If so, how do I properly dispose of it afterwards?

[Borek]

It is most likely http://en.wikipedia.org/wiki/Poly(methyl_methacrylate)

[vmelkon]

If it is poly methyl methacrylate (Plexyglas), gentle heating would soften it. Too much it would cause it to decompose and you'll see bubbles in the plastic. IIRC, Methyl ethyl ketone (MEK) melts it. I think people use MEK to glue plexiglas to other plexiglas pieces.