I'm no expert, but here is my opinion.
This is a very interesting topic.:scratch2: I believe that Scotch, Ampex, and Maxell made some of the best tapes that are still good for recording on after all these years. I've never been disappointed with these brands. I always thought that BASF was supposed to be one of the best, but I bought ten used(paid good money for them too) and none of them record well. Could be that I just got a bad lot.
I had also aquired many different brands of older tapes that I tested by connecting an audio generator to a deck and recording tones. Scotch seemed to have the most consistent and flat response at least up to 15Khz. Back in the olden days, they didn't seem to be concerned with higher frequencys, as in engineering documentation I found from Scotch, they didn't list specs for freqs above 15Khz. I was very dissappointed with many of the other off brand tapes that I tested, because the levels were very inconsistent. Needless to say many of those tapes made it to the landfill. I think that they were probably ok in their day, and if they still have recordings on them from years past, that they are ok for playback, but not for new recording.
Online, you can find old engineering documentation from Scotch that I found very interesting.:yes: