One of the most frustrating things about working with clay is trying to get a smooth surface. We've already firmed the clay, and that will make it much easier to smooth the clay with your fingers. However, if you want to a very smooth surface that is completely free from bumps, marks and fingerprints, there is another simple trick. Alcohol melts Sculpey.
We can take advantage of this by dipping a paintbrush in rubbing alcohol and then gently brushing the sculpture until the alcohol dries. Minor imperfections (fingerprints) in the clay will be dissolved and essentially buffed out of the surface of the clay. The cool part is that the stronger the alcohol solution is, the "mushier" the surface of the clay will become. This means that you can dilute the alcohol with water to make a less aggressive solution, effectively making a 'finer grain' of liquid sandpaper.
- Start with 91% Isopropyl rubbing alcohol. Brush it over the sculpture to remove large scratches, fingerprints, and tool marks.
- Mix water with the alcohol until you have about a 1:1 ratio. Continue brushing the sculpture with this new mix until the surface is as smooth as you can get it.
- Use water alone to brush the surface. With much brushing you will be able to get an almost reflective polish
Not smooth enough for you? Well, after you bake sculpey you can take sandpaper and polishers to it just like anything else.
Begin sanding with 300-400 grit sandpaper and go over the entire surface of the clay
Continue sanding with paper of gradually increasing grit density, all the way up to 1600
With dry sanding complete, start the process again with the 300-400 grit, but this time soak the paper in water first
Use polishing compound and a rotary buffer (I personally like the Dremel polishing kit)
to finish off the surface. You will be able to get a glass smooth surface with this method.