You can also make your own black stain Mr. Novelist. Pour some vinegar over a piece of steel wool in a container of your choosing, seal that thing up, and leave it for some time (I've read that 12 hours is sufficient) and let that acetic acid eat that thing. I left mine until there was no more steel wool and just rust coloured vinegar but that's because I kind of forgot about it.
Once you have that you're going to need to introduce some tannins to the briar to get it to turn black as that's what this chemical you've created reacts with and briar loses most of it's tannins in the processing. You can get tannin from home brewing stores I hear but I used a strong brew of gunpowder green tea.
Paint the tea on and let it soak in and dry and then paint the other on and you should see results very quickly. I was astonished at how quick it was and just how black. Here's a Grabow freehand I rusticated with a dremel and stained with this very mixture.
Really remarkable stuff and probably pretty darn great for high contrast staining since this stain will not bleed.