Vinegar lack aka vinegaroon
The original recipe:
VINEGAR BLACK
For giving color to the grain of leather there is no blacking that will at all compare with the well known vinegar black. This may be made in various ways. The simplest, and, without doubt, the best, is to procure shavings from an iron turner (note: some folks get the turnings from brake drums) and cover them with pure cider vinegar; heat up and set aside for a week or two, then heat again and set in a cool place for two weeks; pour off the vinegar, allow it to stand for a few days, and draw off and cork up in bottles. This will keep for a long time, and, while producing a deep black on leather, will not stain the hands.
FWIW - I've been using this blacking for 40+ years and here's how I do it most times:
I use de-oiled 4/0 steel wool: dip in acetone, squeeze out the extra and hang to dry - then tear or cut into small pieces. Add one pads worth of the de-oiled steel wool to one quart of white or cider vinegar (I prefer the latter) I use those plastic coffee "cans" and punch a single small hole in the lid to let of any gas buildup. If you let it set in the hot sun it will speed the reaction. I let it "cook" for about two weeks until there is only a light vinegar odor left and/or the bulk of the steel wool has been dissolved. I also keep a new batch "cooking" all the time so I have a constant supply.
If need be for a deeper black, apply a bath of strong black tea first (this increases the tannins) and let it soak in good, then apply a generous amount of the vinegar black. Let set for about a half hour and then rinse with a mix of baking soda and warm water, about a 1/8 cup soda to a half gallon of water, apply let set for a few minutes, and then rinse off. While still damp apply a light coat or two of your favorite saddle oil. Once dry, top coat as normal
Experiment - I test a piece of each new side without oiling to see how well it takes the blacking, if need be I'll do a second black tea mix to darken, then apply the oil which also helps darken.
Instead of steel wool you can use chopped up bailing or fence wire - the smaller the better since it will dissolve in the vinegar bath faster.
re: the smell -
1) Keep adding iron/steel wool until it quits dissolving it, this will use up all of the acid. Also stir the mix while it's brewing in order to aid in the off gasing and to introduce as much oxygen as possible. Strain/filter the mix to remove any left over iron - use it for your next batch.
2) Once done and dry hang in front of a fan - the air movement will help eliminate any residual odor - mine seldom smells for more than a day at most.
3) Be careful with the baking soda rinse, too strong, too long can cause the leather to "burn" - not a good thing. Just a quick dip or wipe down with the NS mix is enough and be sure to after rinse well with clear, clean water - if your tap water is high in iron use bottled water.
fallacies - in reading the various forums I've seen a few - the most glaring one saying to use rusty iron. For leather this can in fact be counter productive - rusty iron can be better for when using this as a wood "stain" when one wants the stain to offer more red tones, but for leather is unnecessary.
bottom line - as Emeril would say "it ain't rocket science......"
