Awesome job on the holsters Navy Six! Welcome to the wonderful world of leather craft!
If it's any help, I have used Marshal's recipe to make my own vinagroon several times, and it works perfectly. It turns leather a beautiful deep black. I do dunk my leather though. It's just faster and easier for me.
There is also another plus to using vingaroon. It doesn't turn your fingers black. It's just vinegar, so there's no mess on your hands. it will however turn some wood black.