To be honest I thought this was too good to be true – until I tried it.
It is simply white or apple cider vinegar with steel wool! Take a jar, put in your vinegar, then shred and add some fine steel wool. (You may need to experiment with quantities to get the colour you want). Allow to soak (I tested mine each day until it was close to what I wanted).
I believe the theory is that the vinegar is pulling the natural tannin from the wood, so different woods will react/colour differently. And I am told (but I have not tested this) that you can change the colour by applying black tea or coffee to the wood before applying the stain.
NOTE: I did discover – while the white vinegar and steel wool was great, and easy to use… the apple cider vinegar stain stank. So I’d be doing that one in a well ventilated space in future!
As you can see in the photo there is a marked difference between applying the stain on day one and applying it on day five!