Thinners are used to thin your enamel paints. Be very careful not to over thin. Do not thin directly in your bottle unless you will be using the entire bottle of paint. When thinning Enamel Paint, use the following ratio as a starting point. Gloss; 3 parts paint to 2 parts thinner. Flat; 3 parts paint to 1 part thinner. Thin paint to the consistency of whole milk.