Differences between stones
The differences between stones are significant. The Belgians vs the Nortons are night and day. I use both, sell both and can tell you the Nortons abrade steel against fixed particles that get smoother as you hone while the Belgians create an abrasive slurry which cuts faster and polishes the steel smoother. It's a completely different way to get an edge on a razor or anything else. The belgians don't have to be soaked as they don't absorb water; all of the action takes place on the surface in the slurry.
I currently have two folks who have purchased coticules and blues who are looking at them under high magnification in materials laboratories. They're both saying there is something quite different going on with the belgian influence on the steel i.e. no ragged edges on the steel and no waves in the bevel on the edge of the blade. They've both used other stones prior to going to the belgians.
The belgians come in a variety of colors, shades, and with various amounts of "figure" in them. Regardless of all that diversity in this very natural product, the result of their work on a straight razor is an incredibly sharp edge and results are what important. The differences in colors, shades, and figure don't seem to play such an important role with the Europeans as they do with some folks on this list. In fact, if you look at the video of them making straight razors at Dovo, you'll see a woman honing a straight on a belgian coticule that has black lines going across the stone. That is "figure" and is more or less a surface effect. Her honing technique is also completely different from what we use here in the States.
The belgian combination stones are called "natural" stones and I have about half a dozen in stock in 8x3 and 6x2 and they are truly beautiful stones. I don't put them on the website because they don't come in either often or predictably and I don't like to take folks' money for something I don't have in stock and don't like to sell what I don't have. If anyone wants a "natural", let me know and I'll keep you on a waiting list if I don't have them in stock. When I do get them, they don't stick around long!
Howard