I have several Curtas that were in a fire. Soot blackened the most exposed numbers on the dials, mainly the zeroes, nines, and ones. I've tried cleaning the number dials in an ultrasonic cleaner and in a petroleum-based solvent. Neither was entirely satisfactory.

Does anyone have experience restoring the numbers, perhaps using paint? The factory paint appears to be silver or aluminum.

The numbers weren’t painted. What you see is the exposed aluminium that wasn’t anodised. I’d use kitchen cleaner (bleach based) with a cotton bud. Go gently, and you’ll clean the dirt off. Don’t worry about removing “paint”, because the numbers aren’t painted.