I am planning to mix Tamiya flat white with a little of their flat black to come up with sort of a "dirty white" color for my next model build. Is there anything special I need to do when mixing Tamiya acrylics? For example, should I add thinner when I mix? Or just mix them straight out of the bottle? Would it be OK to just add a tiny amount of black to the white bottle until the color is what I want, or should this be done in a separate jar?
Also, when storing the mixture, will it keep for a while? Obviously, I would re-mix it thoroughly before use, but is there any problem with the colors separating or breaking down over time when being mixed? I would assume that because they are both acrylic paints of the same manufacturer, they would mix together easily, but I just wanted to be sure.
Any other tips for best results?