Just happened to stumble across this thread and thought I might chime in. I'm one of those straight razor forum members someone was suggesting might be able to help.......and far from an expert, but I do have a couple thoughts for you here
It's hard to tell from your pictures, but I don't think BBW is right here. Like others have said, the slurry would most likely me more bluish/purplish. And my experience with natural coticules with BBW backs is very limited, but the one I have (and most pics I've seen) have a bluish/purplish shimmer to them
If it is a Thuringian, that would be a great find, as those are fairly hard to come by and are always grabbed quick when they pop up on the razor forums. From what I've read about them, they are a natural rock mined in the Thuringia region in Germany before WW2, the mines have not been operational since, hence the scarceness. I've never had a chance to try one, but never hear anything but great reviews about them as a finishing stone for razors. One of these days I'll get my hands on one and find out for myself.
Hones I have that look similar, from what I can see:
1) "Chinese 12k" / "C12k" - as found on eBay and sold over on woodcraft. As the name suggests, is believed to average around 12k grit...though, as any natural stone, this may vary. Very dense stone, doesn't absorb a noticeable amount of water.
Medium gray, sometimes with dark grey streaks (mine has long, thin, very straight streaks, almost black) when dry.
Dark grey, not black, when wet.
Looks similar to a big block of graphite in those respects
Greyish, milky slurry similar to yours.
2) From a set of Welsh slate sold on eBay, this one is nicknamed "Dragon's Tongue". Estimated at approximately 10-12k
Very dark grey dry, jet black wet.
Slurry is dark grey with a hint of brown.....kind of looks and smells like watered down modeling clay. May sound crazy to mention the scent, but the scent is fairly strong on this one, you'll notice it as soon as you start raising a slurry, unlike with the C12k
3) Also from the Welsh slate set, nicknamed the "Welsh Thuringian". If I remember right the name is because it looks and performs similar to a Thuringian hone. Estimated around 15k
Darker grey than the C12k dry. Wetting it only barely darkens it at all. May have wispy streaks throughout that sort of sparkle when looked at from the right angle
And again with the smell.....the slurry looks very similar to yours, smells a lot like you just finished holding a handful of pennies in a sweaty hand (not pleasant, sorry, but it's the only thing it reminded me of lol)
All 3 of these I only use after going through 1k, 4k and 8k stones. Both of the welsh slate stones I've used with a light slurry followed by just water on the clean stone, or just water.....don't recall noticing a difference using slurry first. The C12k I've only used for finishing with water.
Whatever it is, the fact that it's working for you is the most important part! But if you really want to narrow it down just for your own curiosity, I hope the information above helps point you to something useful
but, man, taking a second look at your pics.....is that greenish streak in the first pic par of the stone? Or part of the slurry?
If it's in the stone, I'd lean back towards Thuringian (maybe Escher? but without the box/paperwork there's no way to say for sure).
Once you get into natural stones, the varieties and subtle differences get to be a bit mind boggling
Here's a little extra info from a more experienced source than me: http://www.theshavingroom.co.uk/forum/thread-22512.html
Edited by kavik79 - 4/6/14 at 10:51pm