Going back to Henry Hellmers' batch book, Akro had seven formulas for what we call oxblood, all stolen from M. F. Christensen and brought to Akro by Horace C. Hill. Six have 6 ingredients, beginning with sand, and the other 5 (soda, limestone, litharge, red iron oxide, and brass dust) vary a little by amounts from formula to formula. Some have Hellmers' notations like "good color," "best so far," or "red glass but metal specked."
The 7th formula has 9 ingredients, adding zinc oxide, red copper oxide, and borax. The notation is "best made and last under Hill."
But as has been suggested up there ^^^ and elsewhere, you don't have to be trying to make oxblood to get it. And conversely, you can try to make it and fail.
You can stumble into oxblood using cupric (copper) oxide, among other things. And out of it any number of ways. A kind of "Goldilocks" (just right) color.
It's definitely a little tricky.
Personally, I guess I think of MFC and Akro as the "classic" oxbloods, but I don't think of them as the only "real" ones. After all, MFC bought its formulas from J. H. Leighton, and most people wouldn't deny that some of those nice early German ground-pontil marbles have oxblood too. I have one myself. Just one, though sigh.
Alley & others either had it or had something very like it, perhaps accidentally at first and then later by design, with varying degrees of success. I have a couple of Pelts that have it.
At any rate, I think it's oxblood whether intentional or accidental, and there are more ways then one to make it. JMO.