Agree that looks like oxblood (and yup Bo, to me that looks like a japanese mib, and yup very cool - wouldn't mind having it!) And agree the ox(like) part is accidental.
Fwiw, Gary, my suspicion is that it likely is copper based. I don't THINK that old marble makers used aventurine on purpose. But I do like to think they used copper-related colors. I want to believe. ;-)
M!b$ pic shows a trend I've seen. When we think of accidental ox - the kind of glass which many non-newbies might agree looks oxlike - we are most often looking at things in a blue to green range. Or so it has seemed to me. And whether or not mib makers used copper-based colors for that range, it is true that SOME people used copper to make those colors, at least the aqua shades.
I started a thread at LOM about the aqua <--> ox connection. Here's that link in case anyone is interested.
*whew* now I need to put my head down. This is such a heavy subject. :-)