Stearic acid or sterine is an animal or vegetable fat byproduct. It is used to and make the candle burn longer. I have also found that the color fades faster with the stearic acid than with the other additives. One of the things I like is the colors will come out brighter and the candle will be more opaque. If you want a white candle, Luster powder is a good option to achieve this.
Clear Crystals are also in the polymer group.
The burning qualities are the same as the Luster powder. The purpose of these crystals is to keep the natural glow quality of the wax. It does not change the opacity of the candle. There are two types, one for container candles and one for molded candles. There are quite a few different types of molds.