Dave and Rudy, 
It is important to remember that brown oxide by virtue of it's shorter 
and much more densely packed crystal strucure has a much greater 
surface area than black oxide. Thisprovides the pepreg with many more 
bonding sites with which to grab on to thus improving the bond 
strengths.

Also I have performed a number of test on the composition of brown and 
black oxide coatings. I found that black oxide contains a much greater 
proportion of thermally unstable cuprous oxide than does the brown. 
During the lamination cycle, the cuprous oxide can decompose forming 
oxygen, thus contributing to delamination.

Good luck