brush enamel thinning?

Thin until with a fine stroke brush over and the pigment can easily cover the background color. If paint is too thick, u will have difficulity painting it smoothly

How do u know thinner is added too much? Too watery until it has great difficulity achieving even color even with repeated brushing.. If too much thinner added. Either let the paint evapour some of its thinner or you just have too repeat more step painting of layer.

I don't thin them at all when they're new or relatively new...Never have.. Most are formulated for brushing straight from the bottle...  If you're using old paints, thin them back to the consistency they had when they were new..