Mixing colors inside of a mould can cause the color to stick to parts of the mould. While still mixed with the resin, so it is not a soft spot, the color is "on top" of the resin.
Mixing colors inside of a mould can cause the color to stick to parts of the mould. While still mixed with the resin, so it is not a soft spot, the color is "on top" of the resin.