I have tested many different methods for polishing resin, and some are definitely better than others. I like my resin to shine like glass; if it doesn't, it looks inferior to me. Now, this is just my personal preference. If you are going for a dull finish because you want your resin to emulate granite or stone, that is a whole different issue.
First, let me tell you about a couple of the other methods I have tried for polishing my resin that just didn't work for me. As I mentioned above, I have experimented with several different techniques, but the ones I am listing here are the most common:
Castin' Craft Resin Spray:
I have had mixed results with this product. It tends to be unpredictable and may/may not work depending on several factors including the level of humidity in the air and the temperature outside. (Note: This product really should not be sprayed indoors. The fumes are noxious and good ventilation is needed. I strongly recommend spraying your projects outside.) On mild days when the humidity is low and the temperature is mild (between the 70's and 80's), the product works fine when used as directed. Unfortunately, if the elements don't all fall in line, it can spell disaster for your projects. I found this out the hard way - more than once. In this situation, the spray will come out a cloudy white color, instead of clear. The cloudiness does not go away when the spray dries and the project is ruined at this point. I was able to rescue a couple of pieces by quickly wiping my finger over the sprayed item. (I know - this is a big no-no. Do as I say and not as I do.) Given the fact that I make hundreds of pieces of resin jewelry at any given time, the unreliability of this product is not something I wish to chance. I don't know about you, but the thought of tossing out several pieces of resin that took days to make does not appeal to me in the least.
Carnauba wax is an item used to polish automobiles. I read that this item was recommended for polishing resin as it helps to fill in the lines left by the molds, and it leaves a soft shine. When I tried polishing my resin pieces with this product, I really couldn't tell the difference between the coated and uncoated pieces. The lines still showed as clear as day and the resin surface was still dull. Since I like very glossy resin surfaces, this product didn't work for me. It did not give me the end result I was looking for.
By far, the best results I have encountered is by using resin as a coating for the finished pieces. This takes a little longer as you have to wait for the resin to harden, but the results are well worth it. The finished product is shiny and new, and it's virtually resistant to scratches and wet weather. Hands-down, this is my favorite technique to coat resin pieces.
Cut a strip of duck tape (and before anyone emails me about my spelling - the brand I use is called DUCK tape - seriously) and lay it on the work surface, sticky side up. Place the resin piece on top of the tape, face up.
Press the back of the tape firmly against the resin piece, using your fingers to ensure there is a tight seal. This step is important. You don't want the resin leaking underneath the tape.
In a small container, mix up a batch of resin according to the manufacturer's directions. With a flux brush or other disposable brush, lightly brush a coat of resin over the top and sides of the resin pieces. Use a light hand when doing this; only a light coat is needed to get the glossy shine. Any excess resin will form a pool around the completed pieces and will have to be sanded off after it has hardened.Allow the freshly glazed pieces to dry. Remove from tape. Sand edges as desired and wa-la - you have gorgeous and shiny resin pieces to use in your craft and jewelry projects.