I place a burnished bisque-fired ware inside a steel drum with sawdust and paper which I set on fire. The smoke penetrates the surface and produces random decorative effects, making each piece really unique.
Sometimes, I use masking tape, slip or other materials to mask off areas that I want to keep free of smoke.
After smoking and allowing the piece to cool off I wash it and scrape the soot off. When dry, I polish it with wax. Of course that ware is purely decorative and not waterproof.