In the early phase of its technology, magnetic tape could be universally described as brown with one side shiny and the other dull. This description is today the exception rather than the rule. Tape coatings now come in varying shades from light brown to black. Tape backings range from black to brown to red or pink and even yellow, green and blue. Tape textures may be shiny, silk or matt. Tape thicknesses are identified as standard play, long play, double play and even triple and quadruple play. Perhaps most confusing of all are the manufacturers descriptions of their tapes as being low noise, low print, high output, extended frequency range and so on. Finally, cassette products come in another host of forms; ferrous, super-ferrous, chromium dioxide, ferrous-chrome and cobalt - all claiming various advantages.
The tape scene can indeed be confusing, even to the initiated. What then can the oral historian make of it? What is 'good' tape?
Quite a long list can be drawn up of the characteristics which would be desirable for the ideal all-purpose magnetic tape. It should combine good physical strength and flexibility; it needs a chemically inert base, yet one which binds well to the oxide coating; the coating itself should give good sensitivity, exclude distortion, preclude magnetic noise and have a low print-through characteristic; the oxide layer should have a high Signal handling capability without reducing the tape's upper frequency capacity and the texture of the tape should facilitate smooth and even winding.
Unfortunately such a model tape does not exist. Many of the desirable qualities mentioned above are conflicting ones and by incorporating some of these characteristics into their products tape manufacturers unavoidably exclude some others which are mutually incompatible. As a result all tapes are something of a compromise, being geared more to one application than another. The best choice of tape is in large measure influenced by the particular use in mind and, ideally, different types should be selected for different machines and purpose.
The tape characteristics and certain brands which can be recommended are set out below under the three main activities which collecting centres are generally engaged in.
Most portable open reel recorders are not capable of giving their highest possible performance with standard play tape. This is because they have a relatively weak spool torque, which does not give the best head to tape contact with the stiff standard play tapes. For most interviewing applications the greater flexibility , better frequency response and longer playing time provided by long play and double play tape are of overall greater value than the higher signal handling capability, lower print-through characteristics and greater physical strength of standard play tapes. Triple or quadruple play tape, being extremely thin and easily damaged, should be avoided.
Since the original interview will be the recording from which all subsequent copies are derived, it is obviously worth ensuring that one of the best tapes for the purpose is used. Any distortions or hiss due to the shortcomings of the original tape cannot be corrected merely by using a better tape for later copies. Therefore, a tape should be selected for recording purposes which has good signal handling capability with low distortion, low noise characteristics and acceptable print-through figures. Among the range of long play products available BASF LP35, Agfa PEM 368, Ampex 407 and EMI 825 can be used with confidence. Suitable double play tapes include BASF DP26 and Agfa PEM 268. If double play tape is used for recording purposes it is advisable that a standard play preservation copy is made from the original within a week or two of the interview. Other tapes may be appropriate but beware of using unbranded or unproven tapes if you do not have the technical facilities to test them. The advice of the tape machine manufacturer should also be used in conjunction with the above suggestions.
For cassette recording, the best advice which can be offered is to follow the advice of equipment manufacturers (unless you find a brand that gives better results) and avoid the thin tapes marketed as C90s and C120s. It may also be prudent to limit your choice to the major manufacturers. Chrome tapes, which are attractive from the point of view of their extended frequency response, on balance give more problems than benefits. They have been found to wear out machine heads more rapidly than the ferrous types and have unsatisfactory distortion and print through characteristics.
For long term storage any of the major professional standard play tapes can be recommended. Although print-through (the tendency of the signal recorded on one layer of tape to imprint itself on adjacent layers) is not the danger on modern polyester tapes that it proved to be on some of the early acetate products, it is best to avoid tapes which have poor print-through characteristics or are of unknown pedigree for preservation copies. In order of their print-through specifications, the following tape brands are all suitable for archive purposes: Racal Zonal Low Print (which has substantially the best print-through characteristics) EMI 816 and 815, Agfa PER525 and PEM468, BASF SPR50LH, Ampex 406, Scotch 262 and Zonal 666.
The tape backing can be of an important feature on archive tapes. Of the products named in the preceding paragraph, Zonal Low Print and EMI 815 have a shiny backing and need to be wound with some care to avoid ridging (or edging) -which makes them vulnerable to physical damage and general unevenness of the tape. The other brands are all tapes which have a textured backing. This gives a smooth even wind even when spooling at high speeds. If archive tapes are liable to fast winding then a textured tape is the best choice. If tapes are always shelved 'end out' after having been wound at a standard recording speed then - even if shiny backed - they will not usually be prone to edging.
Most major brands of tape with good all round print-through and signal handling qualities may be used for the public reference copies of the record collection. On balance long play tape provides the maximum advantages of cost, durability and space economy.
Cassette tapes have certain advantages for reference purposes. They are less vulnerable to physical damage by inexperienced handlers; they provide a cheap, convenient and compact reference medium; and they can be easily 'detagged' as a safeguard against accidental erasure. General advice on selecting cassettes is given in section 1 above.