Some tips and advice on smoothing Casteline from professional sculptors Adam Beane, Keith Kopinski and Ray Villafane.
...swiped from an old thread on the Clubhouse Forums...
Lighter fluid (Rosonol for a Zippo type lighter) works GREAT!
Only use it dead last!
I think people over-use it and the sculpture gets a very soft, melted look on the high points and is still rough in the crevaces.
For the 5 years I've been sculpting, I've used soley the "hot sponge" method. This also can turn a good sculpture into an indistinct blob if over used.
Basically, try to get your sculpture as good as you can with hand tools. Use the hot 3m sponges very gently to smooth out small sections then finally use lighter fluid on a 3m sponge or brush. The sponges will "load up" so I cut them into small managable strips and throw them away when necessary.
Solvents will also only dissolve the binders in the material, leaving filler, which can result in a "grainy" look.
You can also use an alcohol torch, but I find these to be not very useful.
There is no short cut to a GOOD smooth sculpture other than time and effort. If something on my sculpture is to be smooth, it will be INTENTIONALLY smooth, not the result of some process (like melting) that I cannot directly control. Does that make sense?
Another good way to heat the sanding sponges is to buy a cheap coffee mug warmer and/or candle warmer. It doesn't really scorch the sponge like waving it over open flame.
As for needing to wash a sculpt after brushing it with solvent because it will continue to eat it... I don't think so...
I try to stay away from solvents all together on castilene and just employ Adam's "hard work" theory and let the tools and effort be the guide. (Well the sponges too)
I think the castilene more so absorbs the solvent and can get kinda gummy which isn't very desirable to me...
It just takes a lot of sanding. Solvent at the end does more to simply uniform the surface finish than anything else. In other words the solvent creates a nice uniform sheen is all. It does very little to actually "smooth" the piece out. For a true smooth finish it will take many layers of sanding.
Over using the solvents more than a simple one shot brushing AFTER THE PIECE IS SMOOTHED BY SANDING will only break down the make up of the Castilene causing it to expose the fillers and in the end be less smooth.
Use the solvent to obtain a nice uniform sheen, not as a way to smooth the piece out or else you will screw up your piece. If you use too much solvent not only will the fillers start to be exposed but you will also find that as you go back and try and fix it that you have changed the properties of the Castilene into some gummier material that is near impossible to fix.
So, the moral of my story...sand, sand and sand some more. No way around it