Wash Worries...

Several possibilities: It works better for me with a flat finish before the wash. Also, if you are using a dark wash over a light finish, you may want to wipe away the excess with a clean cloth or cotton bud. I almost always use oil based enamels for washing because they flow better and are more controllable. If used over an acrylic overcoat they will not usually bother the underlying paint. Be sure the wash is very thin, because the effect needs to be subtle so it doesn't look sloppy. Sometimes it is helpful to think of a wash as shading. I often will use a darker shade of the base color for the main wash, using black only for areas which would be stained by oil leaks.

I have to say that when I use washes, things can get messy too, you know...

I usually make my wash with acrylic or water-based artist colours (you know those that comes in a tube). The paint on my model is on the other hand often enamel. This is quite important as there's no reaction between different layers of paint.

My waterbased wash is therefore paint and water (or alcohol for acrylics), to which I add a drop of washing up liquid and some white vinegar. The washing up liquid will break the water' surface tension and therefore ensure that the mix goes - and stays - everywhere. The vinegar will help reducing those blotches that you find on your model once your wash has dried off. Using watercolour based washes (not the acrylics though)also has another advantadge: if you are unhappy with it, just remove it by placing your model under running water!

Hope this helps.