Incubation and Baking Procedures

This page outlines our current procedures and standards for the incubation (baking) of magnetic media, including both audio and video formats. Tape baking is a preservation intervention used to mitigate binder hydrolysis and other forms of degradation prior to playback and digitization.

Table of contents

  1. Equipment and Temperature Settings
  2. General Bake Times by Format
    1. Audio
    2. Video
  3. Format Considerations and Guidelines
    1. When to Bake
    2. Known Behaviors by Brand
    3. Problematic Audio Brands
  4. Observations and Evolving Practices

Equipment and Temperature Settings

We use two scientific ovens dedicated to tape baking:

  • Thermo Scientific Thelco 70M (Model 6550)
  • Thermo Scientific Heratherm OMS180

Both ovens allow for precise temperature control during extended baking periods. Our current standard temperature is 135°F / 57°C. This is an increase from our previous standard of 125°F / 52°C, which proved insufficient for many tape stocks. Based on testing, 135°F has been effective across most audio and video formats, including Ampex, Scotch, and Agfa brands.

General Bake Times by Format

Bake times vary depending on the format, tape stock, and quantity of media in the oven. Below are typical durations:

Audio

  • ¼” Open Reel: ~8 hours
  • 1” and 2” Open Reel: ~20 hours
  • Cassette (e.g., Ampex): Case-by-case; generally shorter durations
  • Early audio-on-video formats (e.g., U-matic, 8mm, VHS, Betamax): Bake using video guidelines

Video

  • VHS: ~20 hours
  • U-matic: 20–24 hours
  • Open Reel Video: ~24 hours

Note: Multiple large reels (e.g., 10”) may require extended times. We determine final bake durations through observation and testing.

Format Considerations and Guidelines

When to Bake

We routinely bake the following:

  • Audio: Most open reel formats, some cassettes (especially Ampex), and early audio captured on videotape.
  • Video: A wide range of U-matic stocks.

We do not bake:

  • Metal Evaporate (ME) video formats
  • DV formats
  • Digital Betacam
  • Most 8mm video formats

Known Behaviors by Brand

  • Ampex U-matics: Consistently benefit from baking
  • Sony U-matics (Red/Yellow label): Frequently baked; results vary
  • Fuji U-matics: Typically do not require baking
  • Sony U-matics (some stocks): May exhibit white particulate shedding that does not respond to baking

Problematic Audio Brands

  • Analog: Ampex (post-1970), Scotch (e.g., 250), Agfa (e.g., 468)
  • Digital: Ampex/Quantegy, Sony, some Scotch digital formats

We refer to Richard Hess’s website for brand-specific guidance and documentation on tape degradation.

Observations and Evolving Practices

  • Baking durations may need to be doubled for formats like 2” multitrack audio.
  • Multiple bake cycles over time may reduce the effectiveness of future baking attempts. Tapes that degrade beyond recovery often exhibit high-frequency loss that cannot be reversed.
  • Anecdotal evidence suggests that Agfa audio tapes may respond better to slightly lower temperatures, but 135°F remains our reliable standard for most cases.

This document reflects current practices informed by staff experience, vendor feedback, and ongoing testing. As formats continue to age, we expect to adjust and refine these guidelines in response to new preservation challenges.