A couple questions about washes

1. Black will be fine but personally I think it's too stark, and I'd mix black with the base paint, plus thinner, to get the wash. You need a colour that is significantly darker than the base colour. I'd keep pure black for washes I'd put over engine grilles and stuff like that where you need the impression of depth.

1 & 2. If you're using oil-based (such as turpentine, white-spirit,..) paints for your wash, DO MAKE CERTAIN your base colour is real dry. Wait several days. If not the turp will lift the paint underneath! Horror! I use washes made with watercolours in tubes (artist's paints) mixed with water and vinegar and dish-washing liquid and that's the safest way I've ever found to apply a wash...
The proportion of paint/thinner is hard to define. Try 10% paint, 90% thinner first. If the effect is not strong enough, apply a stronger wash. Better be safe and start with something weak.

3. I do not varnish at all after washes/drybrushing/weathering because it will dull the effects I'm trying to achieve..! If you need varnish, for instance because you want to seal the decals or eliminate their shinyness, do it before applying the washes. But do let it dry before going on to the next phase...!

Read this first .... http://www.swannysmodels.com/Weathering.html

Firstly, i would like to say that your page is full of great stuff, swanny!
I have some questions, though... I like your use of Tamyia Smoke for engine exhausts, but, how would i duplicate it without an airbrush? is there a way? (please let the answer be yes...) a really short bristled round brush, maybe?

Secondly, DJ said that you are to mix some of the base coat color into the wash... what happens when it's a camo pattern, or two-toned? Anyone? thanks guys.

I don't know how you could reproduce the effect of the X-19 without an airbrush. As an alternative get a womans makeup brush and apply chalks. Try one of those spongy looking brushes. For the wash I use black but also use browns sometimes. Try making the wash with some burnt sienna instead of black and see how you like that.

When I have several colour in the camouflage, my wash is made of a colour called Sepia. It's a very dark dirty brown that lend itself really well to washes.

Based on advice I read in FSM, I go about my washes by first applying several coats of Future floor wax to make a clear gloss coat over the model. This has several advantages: first, you want to do that anyway to make decal application easier, second Future is an acrylic which does not react as easily to most paint thinners so your wash has less risk of damaging the underlying paint, and third it helps the wash flow into the cracks better.

As for the flat black, that probably depends on the colors you are washing over. I have used black on some modern navy jet models and it turned out great. But I use a gloss black beacuse it runs smoother and I always apply a clear flat coat over the top anyway to flatten the gloss from the Future coat.

the only exterior color i'll be washing over is testors olive drab (except for some white, the tools and 30 cals) but thats for the exterior but as for the interior: ( i dont know if the image will show up, if it doesnt there is mostly white, olive drab ammo cans or something, gold khaki and more white) also i am mostly interested in armor models so i just want to know if that future floor cleaner will work with tanks and iff the interior will have to be varnished

Have you tried to use some filters to get the look you want?
sometimes all you need is a filter then a very very light wash to get that used and or fielded look.

the filter should be like 90-95% thinner and 10-5% colors, usually primary colors.
hope some of this helps

i just did the wash and i'm a little concerned about something, when i put the paint onto the model (its the white interior of the tank) it went really dark, almost grey, i would put a picture but i dont know how, is it suposed to go that dark or do i need to repaint, i think it might have been because i had just added paint to the mixture and some was still on the brush, should i have put on a lighter wash and waited?