Been using this mix for 40+ years and here's how I do it along with an original 1800's recipe....
Vinegar black 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.
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 use those plastic coffee "cans" and punch a single small hole in the lid to let of any gas buildup. Let it set in the hot sun which will speed the reaction. I let it set 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.
For the deepest black, apply a bath of strong black tea = cheap like Liptons - first (this increase 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.
For the stink....
1) Use the baking soda wash per my instructions that have been posted above
2) Once the mix gets to the point it will no longer dissolve anymore iron open the container and let it "air" - seems many folks rush this part
3) Hang the finished goods in the sun with plenty of air when weather permits - if not able then hang in front of a fan - any residual acid in the mix is highly volatile and the sun and/or air will speed the volatility.