Recently I received some spruce tanned leather from Sweden. Now I thought it might be nice to darken the colour a little with something traditional and settled on trying out some birch oil. I rather quickly found out that this isn't really available for purchase here in the Netherlands so I decided to make some myself.
The procedure is basically the same as making charcoal, except in this case you place an additional vessel underneath your pot to capture the oil. From a 5 liter paint can size container I extracted a reasonable amount of material and after some filtering I went ahead to test it one some scaps of the leather I had.
I will wait a bit longer to see how the colour changes before I decide to use it further, something to consider as well is that birch oil as a very distinct aroma. Mine also has a lot of smoke scent, probably due to not filtering tiny ash particles out in the first steps of the extraction.