Not sure if your talking antiquing a white horn but leaving it white (no dying). Dying a horn, or antiquing a dyed horn. On traditional horns, I prefer to do some type of dying process and apply a slight amount of grunge. I would suggest the Scott Sibley book for the last two. I know some originals may have been left white and acquired a patina over time. Others appear to have been dyed. Most new white horns or white and slightly grunged horns I see that appeal to me are contemporary or high art pieces. Otherwise, I prefer them dyed. But that's my personal taste.
