I think that's a good representation of Caunter
My recommendation for a wash is to use an oil paint and mucho white spirit.
The aim is to let a 'pin wash' of dark tone run into all the recesses and pool around the detail to provide definition. It's a little tricky to master and demands patience, but is worth persevering with because it gives a very good effect.
I'd recommend raw umber as the oil colour to use for the wash (a light mid-brown).
You need a minimal amount of oil paint - literally a touch on the tip of a fine brush, which you dilute into a small amount of white spirit (artists' quality white spirit is best - it has a finer flow and zero odour. But regular white spirit is almost as good and a lot cheaper).
The technique is:
1. Work in small patches on each AFV / vehicle. Don't try and do the whole thing at once. Practice on a small area first.
2. First, run neat white spirit into the recesses and around the detail on the part of the model you're working on.
3. Then, as the spirit starts to evaporate off the surfaces, leaving the liquid only in the recesses and around the detail, repeat the pin wash but now using the 'stain' - a seriously tiny amount of oil paint dissolved in white spirit. (Oil paint is massively pigmented compared to acrylics, so you can dilute 20:1 or more and you will still get a good colour).
4. Try to guide the stain/wash with the tip of your finest paintbrush only into the areas where you want it to pool and settle - don't wash the solution across the whole surface of the model, because it will stain the whole surface, and give a slightly muddy look, rather than just picking out the detail.
5. The good news however, it that for an hour or two after application, you can rehydrate the wash with more neat white spirit and move around the stain if, say, too much has accumulated in a particular area. (Not a trick you can pull with acrylic washes and inks).
6. You can also build up additional layers if you need to. It's better to start with a very very dilute wash and then build it up, than use too dark a wash to start with.
7. If you prefer a warmer tone, use a mix of burnt umber and the raw umber. A small cheap tube of oil paint will only cost you a couple of quid.
8. If you want to suggest a little more rust / wear and tear (on and around exhausts, road wheels etc), use a highly dilute raw sienna wash - a great reddish brown.
9. For additional weathering of desert vehicles, I highly recommend AK Interactive 'Africa Dust Effects'. This is a pale sandy 'dust' wash - behaves and used in the same way as the oil washes described above - needs to be diluted with white spirit. If you use it neat, it will be too heavy an effect, especially in this small scale.
These are the techniques and materials used on all the vehicles / AFVs in my Western Desert LAF gallery:
https://leadadventureforum.com/index.php?action=gallery;su=user;cat=470;u=577(Obviously there's a bit more room to work with in 28mm than 15mm. The techniques are transferable though
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