Polishing Eyes

An interesting thread (edited slightly) on the ShopTalk Forum:

Question: We are looking to for a way to polish parts made from a clear urethane casting resin, shore hardness 85D. We currently do all hand polishing and the result is a high glass type polish and looks good.

Response: Urethane is designed to be very resistant to abrasion and does not polish the way most plastics do. Most of the work must be processed in a wet operation with a ceramic or porcelain polishing {Precision Ceramic} media in order to provide enough pressure to abrade the urethane. If the starting finish is rough, the {first step using general purpose} ceramic and abrasive (i.e., pumice) will smooth out the surface. The "pre-polish" would be done in the porcelain media using a fine Aluminum Oxide powder - 100 to 150 grit. Start the water level very low (30% ) and then after 6hrs, raise the water level to even with the top of the load. Run overnight. The final high polish would be achieved using a dry process with wood pegs and {Microlyte} polishing cream . It may take 6-12 hrs to achieve the final polish.