I was going to post some pics but was afraid it would be bridge too far in terms of hijacks, but since that boat seems to have sailed and is now half way to Bermuda ...
Here is a pic. I’m talking about subtile differences in burnt burl cork like on Mikes handle. But the mottling is absent on his handle. All the stuff I have seen Steve use on my rods and other of his builds I have seen seem to be like what they call “premium” type on the eBay source I use, where they brag about how uniformly dark it is. He uses it a lot on the upper part of the grips. i assume this is for better wear, but it is kind of a distinct trademark look for him.
I believe this stuff is made by “toasting” cork bits and gluing them back into a composite. I assume that if some less toasted stuff gets mixed in due to “sloppiness” that makes it potentially “inferior”. But this would obviously be only in appearance and not in any difference in physical qualities.
In the pic the upper grip is one of Bob’s custom rods, below that one of Steve’s, and below that the rings I got a few times on eBay. It is of course %100 in the eye of the beholder, but I find the delicate “imperfections” in the in the Meiser handle shown especially lovely. And even though this kind of “cork” is already way cheaper than regular cork of any grade, it seems like the more mottled stuff is less valued and usually cheaper than the more uniform stuff. I got a few of the kind I liked once, but when I decided to do a whole spey rod handle I realized I didn’t have enough. Obviously you want to use stuff from the same batch in a single handle, but if this effect is considered a blemish maybe they tend not to make a lot. I even got some stuff that has more spidery marbling - even cooler - but again only a few rings.
I assume that how you form the composite would effect that. For example in the handle below most of them are lined up parallel.
The more mottled stuff has been harder to find on eBay in large enough quantities, and a lot of times it can be difficult to even tell from the pictures. Possibly they only consider this as stuff for accents and don’t make large uniform batches of it. I don’t really like the look of the extreme cases where they have done this on purpose, and with a vengeance. Sometimes they call that stuff “zebra” cork. It is a subtile mottling due to what I assume are quite small (but not as granular as the more uniform kind) bits of different lighter shades of stuff mixed in with the rest. The overall effect on a whole handle, like Bobs handle above, is just lovely and it feels alive. No comparison. But maybe you would have to actually see the handle in person.
I do realize it is a bit nuts to care about this stuff, but it is addictive.