Scott...
Washes are used to enhance the depth of a recess to give the illusion of depth. When I do a wash, I typically use two types, depending upon the type of paint I use. If I paint the model with acrylics (Tamiya, PollyScale or Testor's Acryl) I'll use a wash of diluted lacquer thinner.
I use two types of wash colors, black and burnt umber, using India inks for acrylic washes and paint for enamels. For the enamels I usually just use a brown and black.
If I'm spraying enamels or lacquers (Testors MM, FloQuil, Aeromaster, etc) I use a mixture of the India ink and Tamiya thinner mixed with some water. You want the wash to have enough color so that it changes the tone of the base color, but not too much that it actually covers the base...you want it semi-transparent. My rules is that you want to be just able to see through a drinking glass.
There's two methods of application that I use...one is to cover the entire model, then drybrush the details back with a base color. The other is to apply the wash only in the areas that have recesses. This is considerably more time consuming, and makes for a 'cleaner' looking model. The overall method is used when you really want to weather or dirty a model up. If I'm doing a wash on a deck, for example, I'll apply the wash to the deck, then go back once it's dried and remove the wash from the raised surfaces, using a clean version of the wash (alcohol and water for acrylics, thinner for everything else). Once that's done, depending upon the level of contrast I want, I'll drybrush the base color BACK over the top. If I really want contrast, I'll oftentimes drybrush an even lighter color over the top.
Sometimes, black is not the right color to use, as in the case with wooden or earth tones, like browns or greens. I use the burnt umber for these colors. I'll use the black for grays and blues, and metal surfaces...you have to experiment with what you think looks best.
Hope this helps. Let me know if you have any questions.
Regards,
Jeff Herne
Modelwarships.com