The so-called "frosting" can occur with natural waxes as the candle wax cools after pouring. The wax turns whitish accordingly. As it cools, the wax can also separate from the container in places if it gets too cold. 

To avoid "frosting" experiment with the cooling temperature. You can also use a mix of plant wax and mineral wax to prevent "frosting". However, we recommend that you pour your candle as close as possible to the solidification point, i.e. at the temperature at which the wax becomes cloudy. This temperature varies from wax to wax, so try it out!