On 11/22/2017 02:52 PM, Tom Gardner via cctalk wrote:
The following answer comes from a retired IBM tape
The color of the coatings on a tape are dominated by the magnetic pigment (or the carbon
used in back coats..which is black)..the earliest iron oxide coatings were based on the
conversion of alpha-iron oxide which is a pale yellow and some what needle shaped (longer
than wide) but non-magnetic to gamma iron oxide which is magnetic. The very early
particles were not very homogeneous and were very highly aggregated....poor conversion as
the early particle were being produced by paint pigment manufactures as a specialty
product in low volume. These were a yellow brown color..but by the 60's gamma iron
oxide of 250-300 Oe was commonly used in the magnetic layer coatings. These were typically
brown to chocolate brown (if they had some carbon black mixed in for surface conductivity
(anti-static) which depending on the use as well as the manufacturer varied a lot i n
surface finish (gloss) as well). This market was driven by audio primarily and dynamic
range and analogue signal characteristics such wow & flutter were driving formulation
and magnetic particle development.
In the late 60-s and 70's new particles began to enter the market..Cobalt doped and
later cobalt 'modified" gamma iron oxide as well as chromium dioxide..and some
very early explorations of iron metal particles and some exotic mixed metal crystals...
The colors of the magnetic coatings based on more acicular gamma iron oxide made
specifically for the recording market were now reddish brown , cobalt doped were a dark
brown - to black, chromium dioxide is very black..remember during this period digital
recording in both tapes and disks were now the growth areas driving new pigment
development and drastically improved formulations driven by the need for improved
durability, longevity and wear characteristics (drop outs (defects & debris), head
wear and head/drive contamination being increasingly problematic)..in the 90's metal
particle and BaFe pigments took over tape while disks moved to thin film magnetic layers.
As for reel materials and hub evolution..the initial reels were metal and
expensive...plastic became normal in the 60's and beyond for the most part..but for
master copies or sensitive archival reels..glass or metal were preferred... but changes in
the materials were driven by the higher tape speeds,tensions and demands for improved
reliability and durability. Hubs in some drives had to be conductive so had carbon black
or metals added to them to improve the compressive strength and conductivity. A lot of
very innovative but subtle design features moved into tape reels/hubs specifically
designed for various transports and industry demands. In addition lubrication and binder
changes were common as the needs for the various products in audio, video and digital
Hope this helps..but if the interest is primarily in getting a useful detailed knowledge
of a particular tape..color is pretty much useless..you need SEM/EDAX and GC/MS and a
database of tape analyses to compare to in order to really begin..and then to really know
the tape you need DMA/DMTA mechanical analysis, and AFM/MFM surface profiles.....but to my
knowledge only IBM had that data and I imagine it ..like so much of that knowledge learned
from 1962-2008 is now gone.
Thank you for a very detailed answer, Tom!
What's surprised me is how the 60's tapes have survived so well. Most
of the problems that I've encountered have been with leaky leader
splices and missing BOT markers--and a few broken flanges, all easily
FWIW, I repair flanges when the pieces are still intact by slipping a
sheet of Tyvek between the tape and the flange, then solvent-welding the
flange pieces back together using MEK sparingly. The result is quite
solid after a day of drying--and the Tyvek keeps any MEK out of the
I can usually pick up where a BOT marker used to be by shining a strong
light on the back of the tape and slowly unspooling it until I can see
the faint outline of where the BOT marker used to be and then apply a
new one. Many tapes seem to lack EOT markers, but that's not an issue
for these tapes.
Dried-out glue on paper labels can be replaced with a bit of Scotch 77
As far as redoing splices, I use a VHS tape editing kit. Works very well.
80's Memorex tapes, however have taught me to be cautious, some of them
get very sticky.