Reconstituting Art Clay Copper?

Does anyone have any advice on bringing a lump of Art Clay Copper back to life so I can work with it? I have about a 20g piece which is rock hard despite being stored in a small plastic container.

I know how to do this with silver clay, but am wondering if there is a special way of dealing with copper clay?

Any suggestions would be much appreciated :D

Thanks in advance!

I'm no expert with copper clay but I found it hardened and oxidised very quickly - despite being in an airtight container. In principal the reconstitution of a very hard piece is the same as with silver but any oxidised bits need to be cut out as they will ruin the finished piece.

It's a shame that it only seems to be available in 50grm packs at the moment - its quite a lot to open and use all at once.