Good topic and since my living is made from making various things a few points come to mind. The only clear answer is chemical analysis, yes there were many chemicals available as were natural dyes which is what I use. I like the enhanced figure I can get on some horn but my buying public likes the aged look as do I. That's also why I stain a rifle but even way back when the beauty of anything can be enhanced depending on ones perception of beauty.
Back to horn, my contention with some of the color we see on originals is the atmosphere they have lived in. Think wood/coal smoke, dank dark places like cellers or attics for that matter, time has the effect of age which is what we try to accomplish in short order. I don't know any collector that is willing to have a bit of patina scraped off for analysis. Then again which horns would be likely candidates for testing. We speculate today of what was used in the day, my thoughts are that there wasn't as much as we want to glamorize. The topic of aging can cover every area of work in this time related field.
Bottom line is the person making the piece should continue to do what they enjoy, period! We do have fun doing this don't we? or do some just like to pee on others efforts for their jolly's.
A fine horn, sorry for rambling.
Best regards,
Mark