translucent stones that pass light are more reliable in terms of what you're getting. If you have a 1/2 inch thick stone that passes light really well, it will be a good stone. The worst it could be is potentially a little slow.
Black stones are all over the map. The stones that Dan's sells in the US are as fine as trans stones (and will be unless they relax their standards). Many others are not and there are some unscrupulous sellers selling black stones with visible pores in them. They're just black colored soft ark stones and often have horrible cutting qualities (not like a nice white or colored soft stone with some bite and consistent pore size).
There are white stones as good as trans that don't pass light, but it comes down to specific gravity (same as black stones - if you can find a black stone that is mid 2.6x in SG (just under 2.7 is the theoretical max), it will cut with a trans ark in fineness, but if you like to see the swarf blackening...well, it won't really participate in helping with that.
I haven't seen any other black stones as fine as the ones dans is retrieving. Not norton or anyone else. Anything that's around 2.6 or a hundredth below in specific gravity will show visible tiny pores. Fineness in ark stones is generally determined by how much air there is in the stone, and there might be some folks who prefer a stone with a little bit of bite, but I like them as fine as possible.
I've had some later mex. processed norton trans stones that are a little more aggressive. Before they're oiled, you can see tiny pores on them and they don't pass light well. They just barely pass it at half an inch thick. The ones I've been able to measure (regular in shape) are about 2.6 SG, which is where I get my numbers.
