Samples of oak that have been finished in a variety of ways: fumed with ammonia, shellacked, finished with oil/urethane, including several combinations thereof. The fumed samples were exposed to ammonia for about 9 hours, which may be longer than necessary. They got darker than I thought they would. I tried shellacking prior to fuming and also shellacking after fuming, and the result was quite different. The reddish tint of the garnet shellac was more pronounced when applied prior to fuming.
Later today, I will try a four hour exposure to the ammonia fumes and compare.