Manray, I know we discussed this in the e-mail but I thought since I typed all this up I should post it in case someone one else might benefit from it. (Or not.)
First: you will need enamel paint as your base coat (Russian armor green), and you can paint the model while its on the spruce or when it's built. But after the model is built and painted with the base coat (tank treads and equipment like shovels not added yet) I like to add some putty or plaster of paris to the underside and any place mud can get. Later I will paint the putty or plaster the color of dry or wet mud depending on the scene.
Second: you will need acrylic gloss black ( I use Model Masters I'll tell you why in a second), and you will need Testors- Model Masters acrylic thinner. And is what you need to do is make a "dark wash", I have found that Model Master paint with this thinner make the best dark wash I have used. First put about a 2 oz. of thinner in a small container and dip a medium sized brush in the gloss black. Then swish the brush in the thinner in the small container, the result should be a dark soupy mix but not too thick, it should be runny. You may need to add more thinner if the mix is too thick or if it covers the paint on the model.
NOTE: some people airbrush Future floor wax over the model before they dark wash it to protect the base coat. Using an Enamel base coat and an Acrylic wash work in almost the same way minus the glossy finish.
Dark Wash--- this mix is meant to be brushed over the model, and the mix will run into all the low spots and into all the lines on the model. Now the reason your base coat is enamel and this dark wash mix is acrylics is so the base coat will not be damaged by the dark wash mix. And what you’re left with is a nice contrast and really nice shadows. (Be sure to brush the dark wash over the mud as well.)
Third: After the wash has dried at least a day you can now dry brush. To dry brush you will need the base paint color (Russian armor green) and light tan color, both from the same maker because we're going to mix them together. You will also need a soft brush you don’t mind messing up a little. First get some aluminum foil about the size of a sheet of paper and use this to mix the paint together on. Dip the brush in the green and wipe it onto the foil about four or five times in one spot. Then clean the brush off and dip it in the light tan once and proceed to mix in up into the green on the foil. You should be left with a slightly lighter green color.
Dry brushing-- this technique will bring out all the high spots on the tank and tighten up the edges to bring out the detail like bolt heads and handles. Using the same brush you mixed the paints together with wipe most of the paint off of the brush on to a old white sock. Why a white sock so you can tell when most of the paint is off the brush. Then on the bottom of the tank in a "test" spot where no one can see it, test the brush on the model by lightly brushing the model very fast up and down. You should barely be able to see the paint that comes off. If you see big blotches of paint then you need to wipe more off on the sock before you try it on the tank again. Once you get the hang of it try it very lightly on the top side and "ALL" over the tank. All the detail should start to show up
nicely.
Fourth: Mud wet or dry and Dust...I should have added this at the top but you will need to paint the mud before you add the dark wash. If you want dry mud all you will need is a "mud" color if you want wet mud you will need a Gloss mud color. FOR DRY MUD-- Paint the mud and let it dry then do the dark wash. After you dry brush the tank you can then dry brush the mud, using the same light tan paint mix it with the mud paint the same way or you can make the dry brush color lighter by adding more tan. FOR WET MUD-- after you paint the tank, and then paint the mud the gloss Mud color and then dark wash it all. That’s it for wet mud no dry brushing on the wet mud, it should look shiny and dark, not dry and light. DUST-- (I have not tried this yet.) I have read that Tamiya dust color can be airbrushed on to the model very lightly to give the appearance of, you guessed it dust.
Finally: The above is what I call the weathering basics, others might add more but if you are new to modeling this will add great detail without adding too much cost. You could add oil streaks and muddy foot prints or fuel stains and rust if you like. Of course it's up to you how far you want to take it. This is one of the MANY techniques out there, and I'm sure someone else has a better way. If you do please post it so I can "borrow it"
Good Luck, Ooo yeah post the finish pix Please.