Gizamo,
I gave up using vinegar many years ago when Cathy and I lived in a remote Eskimo village. Vinegar was expensive to ship in by air and try finding onion skins. So I went to the aniline dyes. They gave me good results and I never thought about experimenting any further. I have trouble keeping up with requests for horns.
Read the label on the vinegar, most now days is not real apple cider vinegar. That horn of yours looks very nice. Sorry to take so long in answering, spring is here in the rockies, at least in my little valley, and we are busily getting ready for summer.
Scott