Baking Your Tapes is a Recipe for Success: Part 2

Part Two:Follow up, and, what about the mold?
by Rich Rarey
PUBLIC DOMAIN column for October 1995 Radio World Magazine

Our Readers
We've received engaging E-Mail from several readers for our "Bake the Flakes Back into the Tape" column of several months ago. Greg Guarno asked us the following:

1. What are the audible effects of 'baking' the tapes? I have heard that it dramatically increases 'print through', and that it may erase some of the high frequencies.
2. Are Ampex or 3M now using a different binder chemical, and if so, has it held up any better? We have been dealing with this problem for many years,and it seems to me that I've encountered this sort of shedding on tapes that are only 4 or 5 years old.
This would mean that they were manufactured AFTER the symptoms were already known, which suggests to me that they went on making the defective tape for at least some time.
I should add that tapes that are VERY old, from the 50's and 60's, do NOT seem to exhibit this shedding.

"Baking tapes leaves no audible effects, and it won't affect lubricants, additives or plastic reels."
I posed these questions to our two tape experts: William Lund, senior technical service engineer at 3M, and to Tom Neuman, senior staff engineer in charge of the Recording Technology Group at Ampex. Both experts said baking tapes at the prescribed temperatures will have no apparent audible effects.
Neuman says a temperature at 120 degrees F does not affect lubricants or other additives, it does not destroy splices, plastic reels or leader materials. He adds that after personally baking 2,000 tapes, he has not noticed any adverse effects. Lund says that high frequencies do reside nearest the actual surface of the tape, but unless that surface is disturbed in some way, the baking process does not change the magnetic properties of the oxide particles which make up the magnetic coating of the tape.
In Tom Neuman 's opinion, the only risk during baking would come from stray magnetic fields inside the oven from the electric fan motors, heating elements or solenoid coils. He adds that it's a good idea to check for any such stray fields before baking a tape in an unknown oven.
What is print-thru? A definition Print-though, according to our old Audio Cyclopedia, is the "unwanted transfer of a signal from one layer of tape to another by magnetic induction". According to Bill Lund the print-through phenomena is also not well understood and even more elusive to quantify.
He says it is a characteristic of the oxide used and how it is prepared for use in the chemical binder of the tape. Interestingly, print-through reaches a "terminal value" after a period of time. That is, the tape will achieve the most print- through it can have, and the amount of print-through thereafter will not increase.
The time it takes for a tape to reach this "terminal value" is dependent on the tape (and the oxide used on it) and the storage temperature. Lund says that since the oxide and the tape are pretty much fixed, the biggest variable is temperature. A tape stored at a very low temperature will take a considerable time to reach it's terminal value for print-through, whereas a tape stored at high temperatures will achieve it's terminal value much more quickly.
The terminal value is the same in both cases, it just takes much longer to get there at low temperatures.
He advises not to worry about the 'baking' process and it's potential for causing harm to the valuable tapes, because it doesn't happen.
What's different
What are Ampex and 3M doing differently? Tom Neuman says that when the sticky shedding syndrome was first noted and the effect fully understood about nine years ago, ALL tape manufacturers began the process to improve the tape's archival stability.
Bill Lund points out that "you do not build a new binder and chemistry overnight", but rather attempt to design new tape stocks with greater longevity. He points to 3M's 900 series of tapes as such an attempt, but cautions that even with all manufacturers using accelerated aging tests to predict the behavior of their product, the outcome is still...a prediction.
The binder problem did not appear until 7 or 8 years after introduction of the product, and since predictions didn't show the problem at all, Lund says it "hit us as a real surprise". One interesting aspect of a particular product's age, Tom Neuman points out, is that manufacturers don't have control over the age of tapes sold by some of the supply houses around the country.
A reel purchased 5 years ago could actually be 8 or 10 years old. Neuman recommends buying tape stock from well known and reputable distributors, and avoiding garage and surplus sales, where, he says,"nobody has any idea of how the tape had been stored or the actual age of the tape."
Bring back the old
tape formulation -NOT!
Why then, with all the excitement over binders becoming unbound, don't the tape companies return to the old tried-and-true formulations that worked so well?
3M's Bill Lund says that in the quest for tapes with higher output, lower noise and lower print- though, different oxide technologies were required. The modern, better-performing oxide formulas are chemically incompatible with the older binders from 40 years ago.
Consequently, if manufacturers were to return to those old binder compositions, we'd see a return of tape stocks that had inferior print-through, maximum output, and bias noise floors.
Moldy, Moldy!
Another reader, Charlie Mayer at Swarthmore College, wrote asking what to do with archival tape that is growing yellow, green and white mold. Apparently this mold is not of the school colors.
Ampex's Tom Neuman provided a ready recipe for restoration:
  1. Open all affected boxes and remove the reels.
  2. Place the opened boxes and tapes in a dry, warm room so that the tapes can thoroughly dry. This may take anywhere from a few days to a couple of weeks.
    DO NOT bake tapes that have mold growth, as this will just bake the mold into the tape, and permanently stain the surface of the tape!
  3. After the tapes are thoroughly dry remove the flanges, if the tapes are on metal reels, and thoroughly clean the mold off with a 3% solution of Hydrogen Peroxide.
    This can be purchased at any drug store. Hydrogen Peroxide will effectively clean off the mold and its antiseptic properties will help to inhibit future mold growth (It also comes in handy if you cut yourself while removing the flanges).
    It is especially important to thoroughly clean any stick-on labels that may be on the flanges as they seem to be great breeding grounds for mold.
  4. Next comes the awful part; load the reel of tape on a transport (after replacing the flanges) and slowly wind the tape forward by hand and inspect the surface for sign of mold.
    If any mold is seen it can be wiped off with the 3% Hydrogen peroxide solution and a TexWipe® or similar lint-free cloth. Follow by wiping the excess liquid off with a dry wipe.
    Pay particular attention to the edges of the tape as this is where mold growth generally starts. The time this step will take varies greatly dependent on the severity of the mold growth and your patience.
    If the entire tape is affected you can use a slightly damp (with Hydrogen Peroxide) cloth held up against both sides of the tape and run the tape through at the slowest speed you have available.
    If you use this method, make sure that you repeat the process several times with a dry wipe to completely dry off the tape's surface before putting the tape back in storage.
    Hydrogen Peroxide is the only material we can recommend for cleaning the surface or backcoat of a tape. It does not damage any of the tape's chemical components and is safe to the user.
    DO NOT use alcohol or other types of cleaning solvents as they may permanently damage the tape!
    In many cases the surface of the tape may be stained from the mold even after cleaning. This has not proved to be a functional problem, just a cosmetic one.
  5. Finally, thoroughly clean the storage box with Hydrogen Peroxide and dry thoroughly. Quite often the box is thoroughly damaged, and a new box may be needed.
    In the case of historical material the original box may need to be cleaned and stored separately from the tape. Mold growth usually initiates from moisture trapped in the box material or inside the box.
  6. Before putting your tapes back into long-term storage make sure there is no trapped-in moisture inside the box. It is not a good idea to put tapes away when the humidity and temperature are high, as this is the air that will be trapped inside the box for the next 20 years.

    Neuman says he has personally cleaned dozens of tapes using this method and it seems to work quite well.
    We wish clean, dry, securely bindered tape to you all.

Author's note: Since these articles were published in 1995, the tape industry has changed dramatically; 3M no longer manufactures recording media, and the division of Ampex that made recording tape has been spun off, and is now known as Quantegy.
Bill Lund is working with 3M in their commercial graphics division. You can reach him at,
or at

Tom Neuman has left Ampex and is persuing interactive media development. You can reach him at

Interestingly, Bill Lund says Quantegy has recently purchased 3M's recording media intellectual property rights and remaining tape stock.