It's most likely a chemical residue from the binder giving up. I've seen
that on all types of magnetic tape through the years, and it can be very
specific to brands and even individual production runs.
I wouldn't worry about mold unless its colored, looks fibrous, and you know
that the tape has been exposed to elevated humidity (in excess of 60% RH)
for a prolonged period.
Nixon Presidential Library and Museum
National Archives and Records Administration
On Fri, Aug 10, 2018 at 3:11 PM, Mint Records <[log in to unmask]>
> Firstly thank to those who helped with my Ampex 478 question the other day.
> Something else has cropped up. I have a pair of reels (A & B of the same
> album) that appear to have spots of a white powder coating the tape. None
> of the other reels i've been sent seem to be affected.
> Is this a type of mold? I haven't seen it like this before, or is it
> something more sinister?
> Tape is BASF910
> Thanks for any advice.