In Session 6: Media Collections, you will learn that the component materials in media collections can contribute to their relative stability or - more likely - their inherent and rapid path towards deterioration. Magnetic audiotapes with an acetate film base, for example, are prone to embrittlement and vinegar syndrome, while magnetic audiotapes with a polyester base may appear more physically stable but have playback issues. How can you tell these two formats apart? In this section, you'll learn about physical characteristics, format sizes, tests, and other clues to help you identify the media in your collections.
The housing and storage needs of media collections are just as varied as the material formats. Choosing appropriate housing and proper storage ensures that media collections are not passively damaged on the shelf; using cautious handling techniques during inspection and playback ensures that media are not actively harmed during use. Additionallly, environmental conditions, especially temperature and humidity, are a major factor in the long-term preservation of media collections.
Reformatting and conservation treatment of media collections can be very expensive but may be the only way to access recorded information. While digitization of paper-based collections can necessitate a camera or scanner and image editing software, reformatting of media formats requires specialized playback equipment, expert knowledge of the format, and complex editing software. You will explore these considerations in this session, with further information on managing reformatting projects in Session 7: Reformatting and Digitization.
If you have not yet reveiwed Session 5: Care and Handling of Photographs of this course, it may be helpful to do so now. An undertanding of some of the collection components encountered there (e.g., colorants and photographic emulsions) will be helpful as you move through this session.
The first phonograph, which recorded onto cylinders and played back the recordings, was invented by Thomas Edison in 1877. In 1887 the Gramophone (which used a disc instead of a cylinder) was invented by Emilie Berliner, and in 1892 he began producing discs commercially. Both types of machines were sold commercially until the early 1920s, but discs soon surpassed cylinders in popularity. Commercially recorded cylinders were discontinued in 1929, but cylinder recorders were still used at least through the 1940s for live recording of ethnographic field notes and for office dictation.
"Soft wax" cylinders were usually direct original recordings (though some pre-recorded "soft wax" cylinders do exist). As the name implies, they are made of a soft, waxy compound and have a distinctive feel and smell, with early cylinders a creamy white color and later light brown versions. Standard "soft wax" cylinders are usually 4" tall by 2¼" wide (taller and wider versions exist), and record approximately two minutes of sound.
Molded or prerecorded cylinders appeared on the market in 1902-03. Made of hardened wax or metallic soap, these resemble shellac. Most molded cylinders are black, though brown, blue, and even purple molded cylinders can be found in archival collections. Most molded cylinders were the standard 4" tall and 2¼" wide, except Kinetophones (used for synchronisation with films), which were 10" tall and 5" in diameter.
As outlined in Sarah Stauderman's Pictorial Guide to Sound Recordings three main eras of discs are found in cultural heritage collections:
- shellac type recordings (1897-c.1948)
- instantaneous discs made either of aluminum or cellulose nitrate on a core (cellulose nitrate discs are also known as acetates and lacquers) (1930s-1940s)
- thermoplastic discs of polyvinyl chloride or polystyrene (LPs and microgroove discs) (1948-present)
Visit the Pictorial Guide to learn more the composition and sizes of these discs.
As you learned in Session 5: Care and Handling of Photographs, film is a composite format made up of a film support with an image and/or sound recording suspended on it. Motion picture film consists of this same basic structure, and is made of one of three types of supports: nitrate, acetate, or polyester.
In addition to the elements described here, you may also want to learn whether a film is a reversal or positive print, find more information about magnetic and optical soundtracks, and consider whether the print is black and white or color. Visit Chapter 2: Film Specifics: Stocks and Soundtracks of the Film Forever website to learn more.
Gauge refers to the format and width of the film in millimeters. Though motion picture film was manufactured in a wide variety of gauges, three film gauges are by far the most common formats:
- 35mm film (commercial movies)
- 16mm (home and educational movies)
- 8mm (home movies)
Of those formats, the 16mm and 8mm amateur films that record events of importance to an institution or person are typically found in cultural collections. For overview of the wide variety of film gauge and formats, visit the National Film and Sound Archive, Australia's website on Film Gauges.
While sheet films have coded notches along the edge, roll films typically have edge codes stamped along the side of the film stock edge. These codes provide information about the film's manufacturer, date, and occasionally even location of manufacture and can provide clues (but not solid evidence) to the approximate year that a recording may have been made.
Manufacturers used a variety of coding systems, but unfortunately not all companies adopted edge printing identification. Kodak used a series of standardized symbols for both 16mm and 35mm film while Fuji used a four character code (e.g., JM48 would be January-March 1948 to detail the approximate month and year of manufacture.
Learn more about edge coding of Kodak films via A Guide to Identifying Year of Manufacture for Kodak Motion Picture Films; for DuPont edge coding, visit Appendix A: Film Edge Code Chart of The Film Preservation Guide; and for information about Fuji, Agfa, and other film manufacturers, visit Film Stock Date Codes.
Nitrate motion picture film was manufactured from the introduction of motion picture film in the 1890's until the early 1950's. Most 35mm film stock during that time period is nitrate film; however, nitrate film bases were never used by American manufacturers for 16mm or 8mm motion picture film. After 1920, many manufacturers, including Kodak, labeled nitrate stocks with "NITRATE" stamped along the edge.
Acetate film bases were introduced in approximately 1909, and formulations evolved from cellulose diacetate to cellulose propionate and then to cellulose triacetate, introduced in the late 1940's and still used today for roll film. Acetate motion picture film often is stamped "SAFETY" along the edge.
Polyester film bases were introduced in the mid-1950's and today polyester film stock is generally used for 35mm films. It is far stronger than acetate film bases and not liable to acetate's characteristic embrittlement or vinegar syndrome. Polyester motion picture films may be identified by the edge stamps "ESTAR" or "CRONAR".
A variety of visual inspection methods may help you to identify the film base composition. For example, when held up to the light and viewed edge-on, acetate roll film transmits very little light compared to polyester roll film.
In addition to the manufacturing details listed above, one of the best ways to identify nitrate film bases is by its six well defined stages of deterioration outlined in Session 5: Care and Handling of Photographs.
Polyester film bases can be distinguished from cellulosic film bases (acetate and nitrate) with a polarization test. When viewed between cross-polarized filters, polyester films exhibit red and green interference colors like those seen on soap. To learn more about the polarization test, visit the National Park Service's guide Completing the Polarization Test: How to Make and Use a Film Viewer.
Audiotape formats are magnetic tape sound recordings on a variety of bases, in a number of narrow widths, with a wide range of magnetic recordable layer compositions. Common formats include reel-to-reel or open reel tapes, audio cassette tapes, and digital audio tape (DAT).
Per FACET: The Field Audio Collection Evaluation Tool, four types of base film were used for reel-to-reel tapes, most of which were ¼" in width (studios used multitrack recordings on ½", 1", and 2" widths):
- cellulose acetate (including cellulose diacetate and cellulose triacetate)
- PVC (polyvinyl chloride)
- PET (polyethylene terephthalate), commonly known as polyester
Audio cassettes were created in the age of polyester tape, but over time were manufactured with four types of magnetic pigment or oxide layers that require different playback settings:
- Type I tapes ( "normal bias") use ferric (iron) oxide
- Type II tapes ("high bias") use chromium dioxide or a cobalt-doped ferric oxide formulation
- Type III tapes use a dual layer tape with both ferric oxide and chromium dioxide ("ferrichrome")
- Type IV tapes use metal particles
Most cassette decks automatically sense the tape type via the holes or notches on the top of the cassette, adjusting bias and equalization as appropriate. For more information on cassette tape identification, see Chapter 3.2.1. Analog Audio Cassettes: Tape Type of FACET.
Digital Audio Tapes (DAT) used tape the same width as audio cassettes enclosed in a cartridge roughly half the size. Some DAT tapes may be labeled DDS (Digital Data Storage) and were intended for general computer data storage.
There are a number of ways to differentiate the various reel-to-reel tape bases. Paper based reel-to-reel tapes look and feel like paper. PVC tape bases were used by particular brands in certain years; see Chapter 2.2 Open Reel Tape: Format Characteristics of FACET for a full list. If the smell of vinegar syndrome isn't present (an indication of deteriorating acetate tape), hold the reel-to-reel tape up to a light: if the tape reel is transparent, it is typically an acetate-based tape; if it is opaque, it is a polyester-based tape. This test may not hold true for double and triple play tapes or long-play tapes, but those are rarely found on acetate-based tapes. Finally, a tear test (a destructive method best used by professionals) can indicate an acetate-based tape from polyester-based tape: when torn, acetate will break cleanly while polyester stretches.
Developed in the 1950's shortly after the introduction of magnetic audiotape, videotapes are similar in structure; a base usually composed of polyester, supporting a recording layer of magnetic particles suspended in a polyurethane binder. For more background on the composition of magnetic tape and deterioration mechanisms, see the section Inherent Vice: Magnetic Media later in this session.
The first videotape formats were wide, open reel such as 2" Quad tape, which were primarily used in television to play delayed broadcasts of shows. Over time, the width of the tape used in open reel formats narrowed, and in the 1970s videocassettes (videotapes housed in cartridges) hit the market with U-matic, Betacam, VHS, and various formats used in camcorders. In the 1990s, the videotape format went digital, with the introduction of DVCAM, DVCPRO, miniDV, and Digital Betacam.
Review the Video Format Identification Guide on the Video Preservation website and the Videotape Identification and Assessment Guide from the Texas Commission of the Arts to examine photos and identifying features of videotape formats.
Later in this session you will review the storage, handling, and environmental needs of videotape collections.
In addition to CD and DVD formats - and the emerging presence of Blu-Ray Discs - there are two other optical media formats that are commonly found in library and archival collections. Laserdiscs, popular in the 1980s and early 1990s, were commercially produced home video formats. Approximately the size of a standard LP, these discs are typically 11.81" in diameter, though smaller versions do exist.
Mini-Discs are rewritable magneto-optical (with a magnetic data layer sealed beneath a plastic coating) devices housed in a cartridge similar to a 3.5" diskette. While playback (or "read" mode) is accomplished using a standard optical media laser, recording (or "write" mode) uses a laser to heat one side of the disc while a magnetic head on the other side of the disc alters the polarity of the heated area, recording digital data.
Refer to the Inherent Vice: Optical Media page later in this session for more information.
Hard disk drives, solid state drives, and various portable, temporarily flash memory devices (SD cards, compact flash cards, and USB thumb drives, just to name a few) are the new common computer media of choice, overtaking the roles once played by diskettes and even portable hard disk drives.
Skim through the "Timeline: 50 Years of Hard Drives" (PC World) to review how the size, capacity, and cost of hard drives has changed since its inception over half a century ago.
In 1971, IBM introduced the first commercially available and removable "memory disk" (or "floppy disk," as it is known today): an eight-inch flexible plastic disk coated with magnetic iron oxide and with 79.7 kB of read-only storage capacity. Later disks - or diskettes - were smaller at 5¼ inches and later 3½ inches but used higher-density storage media and recording techniques. For an overview of magnetic tape and disk technology through the years (or through 1994, when this online exhibit was created), visit the "Storage" timeline on the Computer History Museum's website.
Flash memory devices are just as varied as their magnetic computer media predecessors. Though not bound by the shape of rotating magnetic drives (like traditional hard drives or HDDs), solid state hard drives (SSDs) can be any shape but are typically manufactured to mimic the form factor of HDDs: laptop SSDs are 2.5" while desktop SSDs follow the 3.5" slot sizes.
SD Cards are manufactured in a variety of sizes for specific purposes; the standard SD Card is commonly used in both point-and-shoot and DSLR digital cameras; the miniSD Card was formerly used in cell phones but has been replaced by the smaller microSD Card which is also used in some point and shoot digital cameras. For more information on SD Cards, review "Demystifying SD Cards" on PhotographyBay.