WIP for a 35mm female space pilot:
Looking back at my previous sculpts, the biggest problem I have had was in keeping the final surface of the sculpt smooth. Last night I think I figured out why: the batch of Fimo I bought is too old and crumbly.
So on the wip photo above you can see a darker shade of clay beneath the lighter surface: this is me going over the fimo+sculpey dark blend with pure sculpey, then using alcohol + water to smooth the surface, then baking it, and finally going over the baked surface with fine grit sanding paper, and lastly applying alcohol again to get rid of the dust + scratch marks.
(Ignore the fresh rough clay on her upper legs, I added that after)
Methinks it worked...
Lessons learned: choose the shop you get your poly clay from carefully. Some shops have massive discounts every day, but their stock is old and unreliable. And use a single color clay. Otherwise it is hard to see whether the surface is smooth from shading alone.