Hi Mark,
The horn I did for Gordon Barlow, with the silver wire in the spout and band over the carved base plug was colored by natural dyes. The same ones Mike Small and I have been playing with for years and that is osage orange wood, butternuts and walnuts, boiled/reduced for color, add what you think will give the color you want. In this case the color was almost spot on to the Halstead horn Gordon turned up from the family. The orangish red color was not applied it was in the surface of the horn. The horn is dated 1758, I believe. To my knowledge no one has done a chemical analysis on the coloration of horn, My personal belief is the environment in which the horn was kept over the years, meaning the apparent discoloration of articles from sulfur. Basicly a natural changing of the surface color, but no way of proving the fact without some removal of horn material, don't think any collector wants to do that. lol I wouldn't! Finally the reddish color was imparted from the butternuts, and yes they are hard to find due to the blight. Hope that helps if you're not done already.
Mark