Nono, I get ya. That effect is actually easier done than said. You'll be needing Burnt umber oil paint for that and odorless modeling turpentine.
Before you do this stage (after highlighting, shading washes, drybrushing, decals etc etc) you'll best have to seal your model with satin or gloss varnish for protection. A thin layer, no need for heavy duty varnish yet.
Then it's just a matter of carefully dabbing on some Burnt Umber with a brush, maybe thinned with some turpentine and gently make the streaks. (use very little paint, oil paints are very strong in pigmentation) That will give you a decent, if basic, effect. To give it that extra blast from the spice weasel, you'll have to let it dry for a while, and then 'moisten' it a bit again using some sprayed on turpentine with an airbrush, but it can be done with a brush as well, and then 'feather' the effect with a brush.
That's the cool thing with oil paint, it's not permanent unless you seal it with spray on varnish. So you can adjust and correct until you're happy with it, and then seal it.
You can also do it by using heavily thinned acrylic paints or inks but the effect will take longer to build u^nicely and once dry, there's no going back.
Do not be daunted by oil paints, they're easier used than talked about. I kid not. They're a revelation when it comes to detailing and even black outlining. It's magical, magical stuff.
