Scientists unwind the mysteries of ‘sticky shed syndrome’ and why baking damaged tapes renders them playable again

One of the most commonly reported effects of pandemic lockdown is a day-to-day struggle with maintaining focused attention. And so, when researching some piece of hi-fi news, I sometimes finding myself meandering around the internet hopping from one link to the next like Alice bouncing down the rabbit hole to Wonderland. Sometimes the net result is a lost half hour with nothing much to show for it, but other times this directionless drifting can lead to some pretty interesting and pertinent discoveries!

Here’s one worth sharing, in which scientists have been delving into the world of reel-to-reel tape. (By the way, while this discovery is new to me, it was actually published online last year so don’t shoot me if, way ahead of me in mid-pandemic listlessness, you already read about it months ago!).

An article published on from the American Chemical Society reports how Andrew Davis, a polymer chemist at Washington DC’s Library of Congress, has been investigating the gummy issue of sticky shed syndrome.

Why? Well, the library holds around 200,000 reels of audio tape, including musical recordings, broadcast archives and interviews, and Davis is a member of its Preservation Research and Testing Division. His team is responsible for ensuring the preservation of all kinds of different records held on multiple media.

In the case of reel-to-reel, the most common remedy for tapes suffering from the type of deterioration known as ‘sticky shed syndrome’ is ‘baking’. The problem is caused by the absorption of moisture by a tape’s binders (the compounds that bind the magnetizable coating to the physical tape and/or the back-coating on the outside of the tape). Careful ‘baking’ (thermal treatment) of the tape can drive out the moisture and render the tape playable, at least temporarily, allowing a new copy to be made. However, the precise hows and whys – the ‘science part’ – of such thermal treatments have remained unclear.

“It is a mystery why some tapes hold up and others don’t,” says Davis. “I talked to audio technicians to ask what they do to remedy unplayable tapes. They knew that heating degraded tapes worked, and they used everything from toaster ovens to hair dryers. But no one knew exactly why heat worked, and sometimes the tapes reverted quickly to being unplayable. We are trying to find out why.”

Davis and his team used “modulated differential scanning calorimetry, heat-stage microscopy, and artificial aging to study the thermal transitions which occur during remedial tape baking”.

Image courtesy of Ars Technica

The whole process, and the team’s findings, make for some fascinating reading – whether you want a quick summary or the full scientific presentation:

Read the article summarising the research

Read an interview with Davis by online website Ars Technica: Here’s why “baking” damaged reel-to-reel tapes renders them playable again

View the original research abstract and the full presentation from Davis’ research team: Towards understanding the thermal remediation of degraded archival reel-to-reel audio tapes