I once had access to a black oxide stain that fired to a true jet black in cone 10 reduction (college classes). At my current membership studio, their "black" oxide stain actually fires to darkish brown in their cone 10 reduction firings. I don't know what their formula is, but I assume they just mix black iron oxide and water. I also don't know any details of their firing methodology as far as temps, ramping schedule, or amount of reduction.
Can anyone provide, or point to, a black oxide stain recipe that they know from experience is reliably (as close as possible to) true-black for this type of firing?
I appreciate any help—thanks!