Horizontally split tapes.
5.5 . - - - ,
3.5
3~~-~-~~~-~-~-~-~~-r_-~
2 3 4 5 6 7 8 9 10
This graph shows the variation between the two halves of the tape, the variation is again significant.
Brown Lowry and Smith claim that a 5% acetone extractable content would equal in weight 60-70% of the organic binder being soluble. Practically, this extrapolation is hardly likely to be accurate. When a naturally aged tape is placed in acetone to extract the soluble component of the binder, the material the binder is designed to hold is also removed with the solvent.
Within a few minutes, backcoat begins to show visible signs of disengaging iL~elf from the tape, certainly well before any significant amount of binder has been dissolved. Oxide in small quantities also leaves the tape dUling the process, though this probably weighs more, it is less visually obvious. When a new or artificially aged tape is shaken in the acetone, the loss of oxide and backcoat is much less .
. A 5% extraction of soluble material is in keeping with the work done by Cuddihy. who got a similar result in his tests. Our 5% extraction included a significant amount of backcoat and oxide. components which would effect the measurement of overall weight loss. It would therefore reflect a figure somewhat less than the 60-70% of organic binder materials suggested by Brown Lowry and Smith.
The comhined weight of oxide, hackcoat and binder matelial amounts to around ~O% of the total weight of a tape, the suhstrate amounL<; to around 70%. The 5% extraction refers to the total weight of material including the largely insoluble suhstratc. When the figure of 5% is compared to the possibly removahle amount of material of ~()% the figure derived from acetone extraction is around 17% when comparcd to this, the elTors are also correspondingly
larger. When comparing this to the total weight of organic extractable binder material, which is around 8%, the variations are even more alanning.
Under these sort of conditions, it would seem that it is not possible, using acetone extraction, to determine with any degree of precision, the condition of a given tape. And even if there was a process that would allow us to measure the degree of degradation there is no way of correlating this to performance, and no way of applying a level of restoration to the particular problem. The National Bureau of Standards report concurs, stating that the acetone extractable percentage (or sol content, as they call it) is not a good indicator of the lifetime of a tape [Brown, Lowry and Smith].
If we return to our four questions, we must conclude that there is a great degree of uncertainty in treating hydrolysed tapes, and there is not a really satisfactory method of determining the condition of any particular tape, other than the purely subjective one of playing the tape.
We as sound archivists are faced with a dilemma: how do we treat our hydrolysed tapes?
While putting them in an oven produces results, it seems that the present explanation of rejuvenation is not appropriate. We are putting our tapes in the oven of ignorance. Are we doing damage to the tapes in the process? If we wait while another solution is found will the tapes degrade beyond hope of repair? This is certainly possible with artificially aged tapes, but will natural condition degrade a tape beyond the repairable?
I know as a preserver of sound that I am under pressure to resolve the situation and provide immediate access to the material, and as a consequence I bake a tape if there is a request to use it. Should we then just accept the problems with good grace and be grateful for the tapes that are now playable, and were not before?
I personally think we should concentrate our efforts into finding a suitable way of measuring the level of degradation of polyester urethane binders in the particular case, and to find out if degree of degradation is significant in the most important area, that is, the replay of the tape.
Armed with this information we can then apply the minimum of the potentially damaging restorative work accurately, rather than the haphazard and potentially damaging way we are now.
The author would like to acknowledge the work done by Leanne Brandis, scientist and fellow member of the National Library of Australia's Preservation Services Branch. Ms Brandis performed or set up the laboratory measurements and ensured the accurate realisation of the chemical analysis. Kevin Bradley and Leanne Brandis will be jointly working on the further recommendations in this paper.
References
D. Anglin, Audio Mastering Archive Stability. Ampex Media Recording Corp. Paper for the Audio Engineering Society Inc. 3rd Regional Convention, Melbourne, August 1991.
H.N. Bertram, E. Cuddihy Kinetics of the Humid Aging of Magnetic Recording Tape. IEEE Transactions on Magnetics, Vol. Mag-18, No 5, September 1982.
D.W. Brown, R.E. Lowry and L.E. Smith, Prediction of the Long Term Stability of Polyester Based Recording Media. US Department of Commerce, National Bureau of standards et al.
First Annual Report June 1982 Second Annual Report August 1983 Progress Report December 1984.
E. Cuddihy Aging of Magnetic Recording Tape. IEEE Transactions on Magnetics, Vol.
Mag-16, No 4, July 1980.
F. Layne Ampex Seminar. Canberra ACT August 1991.
Australian Academy of Science, Canberra