Washes help

What brand of washes are you using over the Tamiya paint?

How are you cleaning up the excess? Are you rubbing it off with a paper towell or q-tip? You could be simply rubbing through the paint. Try cleaning up the excess enamel wash with a brush that is slightly damp with thinners.This won't work with acrylic washes, you have clean them up before they dry, which is really fast.

Also, try applying the washes on top of the gloss coat, then apply the matt coat when the wash is dry.

I make my own pin washes by thinning black or dark paints with thinner- very thin!

If I am careful about applying it only to the line, I do not have to do much cleanup.  That is secret to me, getting the pin wash only in the panel lines.  I have a special tool I use- a sewing needle jammed into dowel (handle), and the point ground off so it leaves a very small fork.  Doesn't hold much wash, so have to apply it at several places along panel line.  Tedious, but does reduce a lot the amount of cleanup.

Oil washes with have the same result as enamel and the thinner is basically the same. You certainly should not use an Acrylic wash on Acrylic paint. Are you sure your letting the Tamiya dry properly.

My thinking is the paint hasn’t been cured / dried completely.

What thinner?  For washes I use artist oils highly thinned with turpenoid.  

I was trying to use a wash with tester enamel paint and thinner. What I am thinking is that the tester thinner or paint is too hot for tamyia paint. So I just tried to use an oil wash over a gloss coat and it worked out mucher better than the tester stuff. 

I was using testers paint and thinner and I just switched to the oil paint method and it worked out like a charm