There's not a lot of difference between them if you compare them to something like milliput. But if you have experience with either, you'll notice them. (or Kraftmark would've been daft putting all that money into researching and promoting GS with a different colour)
Kayl has it right. In addition: Procreate's fairly sticky when mixed, but loses that stickiness sooner than GS. It's a little more important to get the required quantities stuck onto the relevant surface, first.
Also, one of the more clay-like qualities is probably that it's very slightly water-soluble. Not that it'll dissolve into nothing if you huff your breath on it, but you'll notice the surface getting a bit more slippery if you slather it with lube water.
PC's a little softer, allows and holds sharper detail, and smooths more easily. These are it's main differences and advantages over greenstuff, IMO. Especially stale greenstuff. (Michael Lovejoy mentions in another recent thread that he finds GS easier to smooth, so YMMV) I've also found it stays workable a bit longer than GS, too. I've had problems when I wanted PC stiffer to poke final tiny details in, left it for an hour or two, and saw it was still too soft
.
Even the grey colour is an advantage – planned that way. I know one of my beefs with GS was that it was difficult to see (small) sculpted details against the saturated green colour. Much easier with PC; though again, YMMV. I know of some who had trouble seeing against the light grey colour.
Lastly, there's the thing about mixing different ratios of resin and hardener to get more brownstuff or greenstuff style effects. And that's the third YMMV, 'cos I haven't noticed a lot of difference in that, myself.
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Warren B.
minisculpture.co.uk – when the server straightens out