Disc / vertical-cut (Diamond Disc series)

2026.01.06
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Disc / vertical-cut (Diamond Disc series)

Image credit: Wikimedia Commons (National Park Service, Public domain)

"Disc / vertical-cut" refers to a "vertical cut" (hill-and-dale) disc, which records signals by displacing the groove vertically (depth) rather than horizontally. While most standard 78 rpm records are "lateral," the playback principle and stylus behavior of the vertical cut are different, making it a format that requires careful attention to compatibility.

This MOPM page focuses on the "Edison Diamond Disc" (commonly known as "Diamond Disc"), a representative example of a vertical cut disc developed by Thomas Alva Edison (1847–1931). The Diamond Disc was a heavy disc approximately 1/4 inch thick, had a rotation speed of roughly 80 rpm, and featured a playback system that required a permanent diamond point, making it a rather unique "dedicated design" for its time.

Features

Image credit: Wikimedia Commons (CC BY-SA 2.5) / Author: Norman Bruderhofer

The key to Diamond Disc is its playback design, which reads the vertically cut groove with a "stylus that traces the bottom of the disc" and transmits the up and down movement of the groove directly to the diaphragm. This is different from machines that use a typical steel stylus to scrape the sidewall of the groove (most Victor/Columbia models), and the sound is created with a special playback mechanism (vertical mounting angle and diamond stylus) in mind.

In terms of physical specifications, the most notable features are the 10-inch disc, approximately 1/4 inch thick, heavy weight, and a rotation speed of 80 rpm. While the disc is thick and hard, it is prone to deterioration due to lamination caused by its layered structure, which makes it difficult to store. In exchange for its quiet sound, it also has some storage quirks.

Identification points (appearance and display)

Image source: Wikimedia Commons (Public domain (US))

The first things that help you identify a record are the following: "thick," "heavy," "80 rpm required," and "basically played on a dedicated machine." If you touch it as if it were a "thin shellac record" with the same feeling as a typical 78 rpm record, the thickness will immediately give you a sense of incongruity. On the label, clues include the Edison-style notation (e.g., Edison/Re-Creation), as well as the fact that double-sided records are labeled L/R rather than A/B. L and R refer to left and right when stored vertically, and are a notation that reflects the company's unique practices.

Also, even if the record has the same "vertical cut," it is not completely identical to other companies' vertical systems (e.g., Pathé series). Rather than simply relying on the name, it is best to check whether the disc thickness, rotation speed, recommended stylus (diamond/sapphire, etc.), and playback mechanism are all the same.

Manufacturing and replication concepts (vertical cuts and layer structure)

Image source: Wikimedia Commons (CC BY-SA 4.0) / Author: Wiki LIC

With vertical cuts, the depth of the grooves becomes the information itself, so it places great demands on the flatness of the disc surface and the stability of the material. To meet these requirements, the manufacturing process for Diamond Disc is complex, and involves molding a core material made from a mixture of phenol and formaldehyde with wood flour, applying a phenolic resin varnish (Condensite) to the surface, and then pressing the grooves onto it.
While this layered structure contributes to quietness, it can also lead to deterioration, such as the surface layer peeling off from the core material. Therefore, when handling the actual product, it is safe to avoid sudden changes in temperature and humidity, and to store and handle it in a way that does not cause warping or pressure.

While this layered structure contributes to quiet operation, humidity and other factors can cause the surface layer to peel away from the core or develop lamination cracks, rendering the disc unplayable. Furthermore, the Diamond Disc manufacturing process has undergone periodic revisions. Early discs from 1912–early 1916 are considered to be in good condition with very little noise. However, by mid-1916, changes in manufacturing methods and a phenol shortage led to a deterioration in surface quality, and discs from late 1916–early 1919 have been reported to have high surface noise even when in mint condition. In the 1920s, increased demand led to shorter production processes, and the duplication process was streamlined. The number of metal molds made by electroplating was gradually increased, allowing for the mass production of press molds. The composition of the core material also shifted from being primarily wood flour to incorporating a higher proportion of china clay, which is one of the reasons for the differences in disc texture and the rate of deterioration over time.

Limitations of this format

Image source: Wikimedia Commons (CC BY-SA 4.0) / Author: Wiki LIC

The biggest limitation is compatibility. Playing a Diamond Disc on a standard machine that reads the sidewall with a steel needle can cause serious damage in a short period of time. In other words, it's not a format where "having a disc means it will play on any phonograph," but rather "the disc and the machine are a complete set."

The other is storage quirks, such as deterioration due to layer structure (peeling, swelling, cracking) and differences in surface noise trends depending on the time period. As a result, even if a record in good condition is surprisingly quiet, it can be said that even with the same title, the experience is prone to cracking depending on the condition.

Improvements to this format (dedicated playback system and quality optimization)

Image credit: Wikimedia Commons (CC BY-SA 2.5) / Author: Norman Bruderhofer

The "improvements" to Diamond Discs were not so much about standardizing the standard as about perfecting the dedicated playback system. The design, which permanently uses a diamond stylus to steadily trace the bottom of the groove and positions the diaphragm parallel to the surface of the disc, was optimized to fit the principles of vertical cuts. As a result, with a disc in good condition and the right equipment, you can obtain an extremely quiet and realistic sound, comparable to acoustic recordings of the time.

Meanwhile, the entire industry was converging on the de facto standard of the 78 rpm record, and from the 1920s onwards, electric recording and playback became increasingly common. Diamond Disc was a format that had perfected its "specialized strengths," but it was also at a disadvantage in the race to become a standard.

Preservation and handling (attention to detail in collection practices)

Image credit: Wikimedia Commons (National Park Service, Public domain)

The basics are to avoid touching the disc surface (groove), support the edges and label, and avoid warping, dropping, and pressure. Diamond Discs in particular have a layered structure, so humidity and sudden changes in the environment can cause them to peel or crack. Therefore, it is safest to keep the temperature and humidity stable, store them upright, and prevent mold and dirt from growing inside the case.

Regarding playback, it is necessary to avoid machines with steel styluses and use a suitable playback system (vertical playback, appropriate stylus pressure, stable 80 rpm). If you are treating it as a document, minimizing the number of times it is played and substituting digital access for the original will ultimately protect the original.

The historical significance of this format

Image source: Wikimedia Commons (Public domain (US))

Diamond Disc is significant in that it pushed forward the vertical cut method as an industrial product, as an "optimal solution" separate from the standard of the disc era (lateral runout 78 rpm records). The compromise of using a thick plate, a dedicated stylus, and a dedicated machine was a design philosophy that sacrificed compatibility for quiet sound and stable tracing, clearly marking a turning point in the history of media.

Furthermore, the disc's structure and studio philosophy (a desire to suppress reverberation) meant that it retained its individuality, making it sound different from other companies' recordings of the same era, even when the same song was played under the same conditions.As the recording industry moved towards standardization and mass distribution, it also served as a valuable comparison point, allowing us to examine how far a specialized, non-standard format could compete.

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