For the scale modeler, this is a fast, easy and effective way to age wood.
To use this process you dissolve some steel wool in vinegar.
The dissolution process will take a couple days. Do it in a glass jar and do not fasten the top down tight because as the steel wool is eaten away, gases evolve. If you have the jar closed tight, it is liable to explode.
You can use that solution to color wood.
If you want to get an aged color, put the wood in the steel wool solution.
Let it soak for a few minutes. As you get experience with using this process, you will learn how long you have to have the wood soak depending upon which would you use.
When you are ready, remove the wood from the solution, put it into a plastic or glass tray and pour tea over it. The tannic acid will react with this steel wool solution and age the wood. As it dries, it will darken.