A quick materials update:

It's well known among those who work leather that black dye is something of a frustration.
Surface dyes (paints) are unpleasant, as when scratched they reveal the tan base colour underneath.

Spirit dyes (alcohol based) give some penetration, but can yield an uneven finish, can 'blue', and sometimes needs a pre-dye to give you a nice rich colour.

Oil dyes are messy and have some VOC issues, but have, until now yielded the best result I could find.

All of that changed this morning...

For the last few weeks I've been prepping a batch of Vinegaroon. It's a VERY old, traditional way to dye leather black.

To prepare the solution you first take a quart of vinegar and heat it to near boiling. Then in go a given amount of iron filings (alternately, steel wool). The stuff is left to sit until the iron is dissolved into the vinegar. As this happens, the solution darkens in colour to near black.

Should anyone attempt this at home, make sure to NOT seal the cap on your jar tightly, as some gasses are generated during the chemical process, and containers have been known to 'pop' from the pressure built up.

When finished and applied to veg tanned leather, the solution reacts to the tannins in the hide that were used to tan and stabilize it. The result is nearly instantaneous and quite amazing.

My solution was finally ready this morning, and I gave it a test on some veg tanned scraps I had about. As soon as the solution touched the surface, a bloom of nice dark black appeared. I swabbed the whole piece and within seconds it was jet black.

After the piece is blackened, you give it a dip in water and baking soda to stop any further acidic reaction.

It's AMAZING that more people don't use this method of dyeing! There's no cleanup, nothing toxic, and the colour is at least as good as I can get from oil dye, while yielding a more historic, authentic result.

As a bonus, the colour can penetrate as deeply as you wish- struck through entirely, if you soak the pieces in your vinegaroon.

I cannot be more excited about this result, all the better that it's an historically accurate way to dye black, which will look fantastic on the cantles of the horsehair sporrans.