I use artist oils for washes and ground powders for weathering. My oil pallette consists of White, yellow ochre, burnt sienna, mars red and burnt umber. I find that I can mix my enamels in with the base oils to make variations. A huge tube of white will go a LOOOOOOOONG way. I will us a wash that is a mixture of burnt umber and flat black on OD - but that's just me
While everyone has thier own process to apply washes, I usually will seal the model in future first (it will protect the base coat of paint), then apply a semigloss (50%gloss/50%dullcote then the required thinning). I will do this a couple of times till I've built up the layers and achieve the effect I am looking for. Then I seal with dullcoat - add powder for mud, rust, soot and seal again with dullcote.
This site was posted here a couple of months back and has been an immense help:
http://www.missing-lynx.com/rareworld.htm
You can see my hellcat here:
http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=5245
It's a good build, you just need patience with the suspension assemby and getting all those %#@ little "c" rings to stay put
BTW, A well stocked artists store (ie: pearl paint, utrecht, sam flax, etc) will have more oil colors than you would think possible.[:0]
3d modelling is an option
a true mental excercise in frusrtation