I like to wait until I have several polymer clay items ready for curing before doing a bake as it seems extravagant running the oven for half an hour with one bead in it. Unfortunately I have discovered that if you are mixing raw and cooked components they need to be baked promptly otherwise they cause each other to crack (this is using Fimo, I am not sure if other brands do the same).
The following unfinished pendant is an example (please ignore the general ugliness). I made a thin convex side using the coloured canes which I baked, I then back-filled this with black clay which I textured and embedded “crystal” gems into the centre.
** Insert time elapse montage here… more than a week, possibly a month (I had a day job and morning sickness in the evenings). **
Large cracks along the edges of the pendant
When I finally got back to the pendant, tragedy had occurred in several ways. Most obviously the raw black clay had cracked around the edges. Then the “crystal” gems (which were admittedly cheap and unlabelled) turned out to be some species of plastic and had melted into a sticky mess.
Previously baked clay had cracked and warped
On checking the other side of the pendant I discovered that it too had a large crack and the edges had warped backwards (probably causing the cracks on the black side) so it was no longer a nice dome shape.
None the less I baked this monstrosity and I will probably cover it again at some point and see if it can be resuscitated.
Another cunning plan that went disappointingly wrong was boiling beads. This came about while I was waiting 2 weeks for baby to arrive. Naturally making beads was the best distraction but I had packed my mini clay oven away and I had no intention of cleaning our food oven. My plan was to boil the beads so that I could store them without them getting mushed and bake them properly at a later stage.
Unfortunately when I finally baked my boiled beads they ended up with tiny cracks in the surface. I am guessing that this occurred because the boiling cured the outside layer but the inside remained raw and so the same cracking happened as it did for the pendant.