Are you worried that heating the cured epoxy might release hazardous vapors? I don't really know for sure, but I've done it many times and I'm still alive and have all my reasoning faculties as far as I can tell! I imagine the small amounts of material we use and the fact that we only do this stuff occasionally rather than regularly means we're not going to absorb toxic levels of chemicals, as long as you use common sense. Of course it's best if you're baking polymer clay in a dedicated oven and not the one your meals get cooked in.
Epoxy does soften at high temperatures, and then hardens again when cool, so there is a possibility that if you put very thin Sculpey over epoxy putty it might distort. But as the Sculpey is going in the other direction, i.e. hardening, and as this process is only for 10 minutes or so, it should be fine.
When I need to soften epoxy, as I was doing yesterday to release an aluminium tube, it took about 15 minutes of heating up the tube with a hot air gun to soften the epoxy.
I don't think hardened epoxy releases vapours significantly. The process is that the molecules of the resin and hardener link together to create the final polymer. Once they have done that and hardened they are effectively no longer toxic. The only problem occurs when there is more of one than the other. Epoxy also has an interesting characteristic, in that it continues to harden throughout its life. It is possible to post-cure epoxy by raising the temperature to around 45 deg C for about 8 hours or so, and this can increase its strength. So increasing the temperature to 130 deg C for ten minutes should actually make the epoxy putty a bit stronger.
I think that's proof of the pudding, then!
Hi, new here but have been watching your very helpful videos on YouTube thanks and wanted to ask if it's possible to rebake the already baked once puppet heads which have a mix of sculpted clay and epoxy putty on, in order to build them up with something lighter than the epoxy... before putting the liquid latex on? sorry that's bit wordy!
I put Super Sculpey over epoxy putty on wire to make two puppets (Adam and Eve in L'Animateur) and baked them, and it was fine. I put the epoxy on first because it is stronger, the polymer clay on its own tended to break near the joints where there was no epoxy under it. The baking did not harm the epoxy.
The stink comes from the baking polymer rather than from the epoxy, so it's probably more important to look at the information on the polymer clay pack. And of course I baked it in the oven in my workshop used for Sculpey and foam latex, not in the kitchen oven. But since polymer clays are sold to kids who only have a kitchen oven, it probably can't be too toxic... I hope.
If I sculpt something in an epoxy putty, like Aves Apoxie Sculpt, I usually have to build it up in layers, letting the first bit get hard or near-hard, then adding more on top. If it is all the same batch, it seems to squish out of shape too much. I haven't done anything with polymer clay for a long time now, and i am trying to remember if you could bake it, then add more on top, and bake again. Polymer clay has the same draggy saggy quality (unlike plasticine which is what I mostly sculpt in), so I would hope so. I will check a book I have on making polymer clay art dolls...
Found it! Here is a quote from Creating Lifelike Figures in Polymer Clay by Katherine Dewey:
"The figures in this book were asked many times. This technique, called 'series baking', lets you build up a sculpture body part by body part, or layer by layer." It then says to use the temperature recommended by the manufacturer of that clay, and leave it to cool down in the oven for an hour after baking, to prevent cracking.
So the polymer clay should be ok for re-baking.
You said you wanted to add a material lighter than the epoxy, so are you using a lightweight polymer clay? I notice that Katherine Dewey builds the polymer shape over a ball of scrunched up aluminium foil, which gives a firm base and also would help reduce the weight. My Adam and Eve puppets had epoxy on the wire, then polymer, and were a bit heavy, though they did work ok. In the case of a puppet maybe you could start with an armature, add some foil over that to build up big areas, and then the polymer clay over the foil. But there are some lightweight clays around now, I haven't tried them. I did try Crayola Model Magic once, which air dries and actually is very light, but was also like trying to sculpt gooey marshmallow, very hard to refine the shapes.