I did some fuming with 26° Be Ammonia. (Nasty stuff) Here are the results. The top samples are before and the bottom are after. The samples of wood, left to right are:
Red oak, oak, black walnut, poplar, maple and mahogany. The base is typical KD construction lumber. (Probably pine)
The most amazing part was the darkening of the finish that I applied over the labels. This was three pound cut of shellac. (A commercial product, Zinsser Bulls Eye amber shellac.) I did not expect the shellac to darken as it did. The second picture includes a piece of the base that was coated with shellac but not fumed.
The blue tape is plastic and was intended to introduce a non fumed area to show the contrast. We can all see how well that idea worked.
:(