I don't know to much other than what I read. It is said the plain green stone is a bit finer than the ones with the purple stripes. If so they must be a super fine stone cause the one I have with the purple strips is about as fine a stone as I have had, including a couple Jnats. Here are a couple pics of mine.
I have a massive charnley that has been my finisher for about a year. I use it after my y/g escher stone and it improves the edge. I do about 90 very, very light strokes with water, though I've been told oil works well on them.
A couple of other things I've "heard" but can't personally attest to:
1) They vary drastically in quality
2) Brown variety are the finest/hardest
3) They are often mistaken for other green stones that are not nearly as fine (might be why #1 is true)
I've been using a very light gun oil with mine, 100 light strokes after a Thuri works real nice. I tried with water only and seem to like the oil a tad better.
I love the look of the red and green varieties. Plus - I have to admit that I also like the name 'Charnley Forest' a lot.
I had one, and it had a bit of red in it. Being Novaculite, I had hoped it would be like an Arkansas stone; it is similar but not exactly. It was very hard, but it didn't have the same feel/feedback. Not bad, just different.
I found that using it after finishing on a Jnat set the edge back, so I moved it along.
I didn't try using it after a Thuri, but if I had to guess, I'd say my Thuri edge would be set back also.
From my understanding, the CF stones very a lot in how fine an edge they can produce. I tried thick oil, thin oil, water, water with a slurry (not easy to do) and found light oil was the best fit for me.
Bit off subject but I just finished a couple of razors I'm pimping on the bay with a welsh slate, the one they liken to a thuri and it gave me a hell of a nice shave. Not quite a coti edge, certainly sharper, maybe a little harsher, but definitely a lot sharper. Went from setting the bevel on a 1k artificial to coti to welsh thuri. Might be my new honing regime.
They're nice oilstones, but based on the three I've owned (and direct comparisons from 100 year old texts), they don't offer any benefit over the hardest arkansas stones... other than looks. They are very nice looking stones.
Of course the price on them seems to have come down a LOT (even tiny ones were going for $250+ a few years back), so they are almost competitive with Arkansas stones for price now.
I've got a little one in a mahogany coffin with a 150 year old note mentioning it being brought over from England and a massive one in a softer wood case that is a breeze to use. I'll try and get some pics sooner or later.
Tried something new today. I finished up a couple razors starting with water and very small amount of dish soap. Did 100 x strokes then followed by 100 x strokes with oil. Haven't shaved yet but got some real nice HHT results.