Let me clue you in to a little known secret.
It's simple really. I am a model railroader and I scratch build all my structures. Not only do I scratch build , I also cut my own scale lumber.
The technique is what is referred to as a weathering technique in order to add an aged look.
It's called "Black Alcohol" stain or "B/A" for short.
It's made by taking 1 pint of rubbing alcohol and mixing in one tablespoon of black India ink. Be sure to use at least 99% pure alcohol and water soluble ink. If the mixture separated into globs of black floating around then you have something wrong. The right mixture will be dark and clear as the ink dilutes evenly in the alcohol. Why alcohol works better than water is that it is thinner so it pools in the cracks and depressions better. It also evaporated faster is it's less likely to loosen any glue.
B/A works on all kinds of stuff. Figures can be painted with it to help bring out details, and in fact that is exactly what we do with little plastic people who inhabit our layouts. The B/A helps to bring out small facial features. The gnome's face has a wash of B/A to help define it's features.
Painted on wood it gives the effect of the wheelbarrow. The idea is to mix a weak solution of the B/A and this way you can give your project multiple coats to build it up just as you want.
Here are a couple of photos for you. Only one wash of B/A on his face and several on the wheelbarrow. If you would like to see more of the gnome look here:
New Gnome For The Garden
Christopher