Different types of resin are used in many crafts and hobbies, such as jewellery making, model cars and trains, even real, people-sized boats. Plain resin can be dull, however, leaving your jewellery or boat with a boring, unattractive finish. For items where paint or varnish is not an option, you can polish polyester resin itself to a gloss. Epoxy resin will need to be recoated, since it does not often polish well.
Prepare the item's surface by sanding to shape and cleaning. The goal of this sanding is to get the item roughly into the final shape. The item you want to polish needs to be clean of any dust before moving on to finer sanding.
Sand the item with fine-grit sandpaper. Once the item is sanded into shape, you need to smooth the surface by sanding lightly with very-fine-grit sandpaper. Sandpaper's grit is marked by number, and higher numbers are finer grit. Specifically, 600-grit paper is usually enough, but 1000 or 1200 is also available for very meticulous work. Place the object under water to sand it if you have problems with dust. If you use a machine sander, use a slow setting or the resin will heat up and turn white.
Clean the item again. Remove any dust from the fine sanding and any grease from your hands.
Buff your item with polishing compound, using a soft cloth. Polishing compounds are found in the automotive section of large department stores or in auto supply stores. Jewellery polishing compound does the same thing for resin but is more expensive.
Polish the item with carnuba wax. Also spelt "carnauba," this wax is commonly used on surfboards, and it can also be found in automotive stores. Carnuba wax can be applied with a soft cloth or with your fingers. This gives the item a glossier finish by filling in any small imperfections left behind by the polishing compound.
Clean the item and sand to shape. Sand the item to the shape you want and smooth any imperfection. Then clean off any dust or grease. Grease on the surface causes resin to dry, or "cure," improperly.
Mix a small batch of epoxy resin. Do not mix more than you need or it will be wasted. You only need enough for a thin coat.
Brush a coat of the new resin onto your clean item. Use a disposable brush, since resin is difficult to clean out of bristles.
Allow the item to cure completely and then sand away any resin drops or pools. The coat of resin should have made the surface glossy and smooth, although it can pool at the bottom of the item. You can sand these pools away, being careful not to mar the surface, and your item will be completely treated.