TIPS FOR HAND-FINISHING PLATINUM (after casting).
Sand off the sprues using #220-grit emery paper. Sand in a diagonal direction, then repeat the sanding in the opposite diagonal direction.
Rotary-file the inside of rings very lightly. Do not remove to much metal in this procedure.
Sand the inside of the rings using #280-grit emery paper. Repeat the procedure using #320grit emery paper.
Rubber-wheel the outside surfaces of the castings. Start with a coarse-grit wheel, then a medium-grit, and finish with a fine-grit wheel. Move the wheel in alternating diagonal directions using overlapping strokes.
Buff-stick all flat surfaces using #280-grit emery paper, then #320-grit paper. Again, stroke in alternating diagonal directions and overlap the strokes.
Using a unitized wheel, reduce the surface scratches left by the empty papers. Start with a #400, then a #500, and finish with a #600-girt wheel. Remember to use overlapping and alternating diagonal strokes.
If porosity is present it the casting, lightly burnish or hammer the surface affected by pits. This can be done using a reciprocating hammer or burnisher. The hammer and burnisher should have surfaces that are highly polished.
Polish the inside of rings with white cutting compound or leave a satin finish.
Hallmark or stamp the Quality according to the alloys used in platinum. For example: “ Plat 90, Irid 10” for 90% platinum or “Plat” for 95% platinum.
The outside surfaces should be buffed with white-cutting, then orange polishing compound. Buff the outside surface with the white cutting compound in a diagonal direction, then reverse the direction of the buffing to cross over the original direction. Repeat this operation using orange polishing compound.
Flat-lap all flat surfaces using a white cutting compound. Clean the surface and repeat the lapping with orange polishing compound. Again, clean the surface when the operation is complete.
Using a muslin buff charged with orange polishing compound, lightly buff the outside surfaces for luster. This should give a very high luster a reflective surface.
(Note: Polishing compounds used are up to the individual. Compounds should be considered for desired speed in cutting or polishing.)