Lots of people have their own techniques for washes.. .I paint with Acrylics, so I do washes with Oils... I tried an Acrylic wash once, but that was kind of ugly.. so we won't talk about that... :-(
I usually spray a coat of Future Floor Gloss before decals (cause they go on better, and easily accept Solvset, and this is good in the battle against silvering)...
I then do another coat of Future, for extra paint protection.. and also to protect the decals..
I let this second coat dry/cure at least 3 days...
Another plus about applying Future to the model is the Gloss Coat will help the wash 'flow' better...
After the 3days is up.. I do the wash with Artist Oils.. different mixtures.. usually using one or more of Black, Burnt Umber, or Burnt Sienna... I thin it with Grumbacher Gum Spirits of Turpentine
I use Grumbacher or Winsor & Newton Oils.. Oils are expensive.. but they last for ever.. I think one reason Oils are good for washes is because they are translucent...
Before the Wash... Coat of Future is on there
For the wash itself.. I just take a lil blob of paint (size of an eraser on a pencil) and mix it in a small water bottle cap full of the Turpentine... Basically.. I'm just making very dirty thinner...
Then I go Nuts just sloshing it on.. especially trying to get more in areas that have lot's of Nooks and Crannies...
I then use Q tips (have a good amount on hand).. to clean up the large flat surfaces... don't wanna be totally clean (cause dirty is good).. but you want to clean up the splotchyness, so it doesn't look like you brushed or spilled the dirtyness on.. you want the dirtyness to look like it's just really in the nooks and crannies.. but you want the finish to have a even dirty tint to it..
Here it is partially clean up with the Q-Tips.. there still some splotchyness.. so I continued cleaning
In tight areas or areas with rough edges (like my Jagdpanther Zimmerit.. Q-Tips are no good.. in those cases I use a clean brush that I keep dipping in clean thinner.. to gently clean up the problem areas.. remember always leaving the nooks and crannies dirty!
After the wash.. I add Pastels.. this starts to eliminate some of the glossiness that the Future causes (the wash also does this).. After that you spray on Testors Dullcote (or I liked to use Krylon Matt Finish - cause I'm a cheapskate!) to get that matte finish your looking for get rid of that Future Glossiness!..
Biggest thing is to have the Future Coats protecting your Acrylic Paint Job.. and letting it dry long enough to be really hard and resistant to the Turpentine.. I find that the 3 days is long enough for me!
All ya gotta do is keep experimenting!!! Hey it's easy your making something Dirty.. lol it's not like Airplanes were everything needs to be nice! that's why we do Armor mostly.. or at least why I do.. Airplanes scare me!!