Radium dial

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Instrument dials painted with radium-based paint

title: "Radium dial" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["horology", "luminescence", "radiation-effects", "radium", "paints"] description: "Instrument dials painted with radium-based paint" topic_path: "general/horology" source: "https://en.wikipedia.org/wiki/Radium_dial" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Instrument dials painted with radium-based paint ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/88/Radium_Dial.jpg" caption="dial painters]] in the United States became a cause célèbre for [[occupational safety]] and [[labor law]] in the opening decades of the 20th century."] ::

History

::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e8/171122-ingersoll-radiolite-ad.jpg" caption="November 1917 ad for an Ingersoll "Radiolite" watch, one of the first watches mass marketed in the USA featuring a radium-illuminated dial."] ::

Radium was discovered by Marie and Pierre Curie in 1898 and was soon combined with paint to make luminescent paint, which was applied to clocks, airplane instruments, and the like, to be able to read them in the dark.

In 1914, Dr. Sabin Arnold von Sochocky and Dr. George S. Willis founded the Radium Luminous Material Corporation. The company made luminescent paint. The company later changed its name to the United States Radium Corporation.The use of radium to provide luminescence for hands and indices on watches soon followed.

The Ingersoll Watch division of the Waterbury Clock Company, a nationally-known maker of low-cost pocket and wristwatches, was a leading popularizer of the use of radium for watch hands and indices through the introduction of their "Radiolite" watches in 1916. The Radiolite series, made in various sizes and models, became a signature of the Connecticut-based company.

Radium dials were typically painted by young women, who used to 'point' their brushes by licking and shaping the bristles prior to painting the fine lines and numbers on the dials. This practice resulted in the ingestion of radium, which caused serious jaw-bone degeneration and malignancy and other dental diseases. The disease, radium-induced osteonecrosis, was recognized as an occupational disease in 1925 after a group of radium painters, known as the Radium Girls, from the United States Radium Corporation sued. By 1930, all dial painters stopped pointing their brushes by mouth. Stopping this practice drastically reduced the amount of radium ingested and therefore, the incidence of malignancy.

Luminous Processes employees interviewed by a journalist in 1978 stated they had been left ignorant of radium's dangers. They were told that eliminating lip-pointing had ended earlier problems. They worked in unvented rooms, they wore smocks that they laundered at home. Geiger counters could pick up readings from pants returned from a dry cleaner and from clothes stored away in a cedar chest."

Safety

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d9/Elgin-WWII.jpg" caption="Wristwatch produced for the US Army during World War II showing characteristic sandy deterioration of radium–zinc sulfide painted hands and numbers. Such a watch should not be opened due to the danger of inhalation of airborne particles."] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/7/71/Radium_dial_radon_experiment.jpg" caption="Three radium dials and a radon detector are placed in a sealed plastic container. After 6 hours, the radon level was 446 pCi/L."] ::

Radium is highly radioactive, emitting alpha, beta, and gamma radiation — the effects of which are particularly deleterious if inhaled or ingested since there is no shielding within the body. The body treats radium as it does calcium, storing it in bone where it may cause bone degeneration and cancer. Inhaled or ingested particles may deposit a high local dose with a risk of radiation-caused lung or gastrointestinal cancer. Penetrating gamma radiation produced by some dials also represents a significant health risk.

According to the United States Environmental Protection Agency, "radioactive antiques [including watches] are usually not a health risk as long as they are intact and in good condition." Accordingly, watches with radium dials should not be taken apart without proper training, technique, and facilities, as radium paint can be ingested by inhaling flaking paint particles.

Chronic exposure to high levels of radium can result in an increased incidence of bone, liver, or breast cancer as shown by studies of the Radium Girls. A 2018 study by researchers from the University of Northampton found that a collection of 30 vintage military watches with radium dials kept in a small, unventilated room produced a radon concentration 134 times greater than the UK's recommended "safe" level.

Regulation

::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/96/220101-BuffaloTimes-RadiumKingOfCures-ad.jpg" caption="Radium was initially touted as a positively salutary substance, as this January 1922 ad from the ''Buffalo Times'' illustrates."] ::

In the United States there does not seem to have ever been prohibitory legislation passed banning the use of radium in clocks and watches. It was only with the passage of the Energy Policy Act of 2005 that the United States Nuclear Regulatory Commission (NRC) was given oversight of the use of radium. Prior to that date, "the federal government had a limited role, if any, in ensuring the safe use of radium," according to the NRC. The element was phased out of use by industry acting under its own volition as superior and safer luminous materials entered the marketplace.

Brands

Undark produced by the United States Radium Corporation
Luna produced by the Radium Dial Company
Marvelite produced by the Cold Light Manufacturing Company (a subsidiary of the Radium Company of Colorado)

Footnotes

References

"Radioactivity : Radium".
(21 June 2017). "RadTown".
Roberts, William Clifford. (2017-10-01). "Facts and Ideas from Anywhere". Baylor University Medical Center Proceedings.
[https://www.newspapers.com/clip/103333171/the-new-waterbury-radiolite-watch/ "Which of These Two Are You?"] (ad) ''New York Tribune,'' May 24, 1916, p. 6.
Claudia Clark, ''The Radium Girls.'' ({{ISBN. 978-0-8078-4640-7)
Ingestion of radium has also been linked to [[anemia]], [[cataracts]], broken teeth, and reduced bone growth.[https://www.mass.gov/service-details/health-effects-of-radium-radiation-exposure "Health Effects of Radium Radiation Exposure,"] Massachusetts Department of Public Health, mass.gov/, accessed June 7, 2022.
[https://www.epa.gov/radtown/radioactivity-antiques "Radioactivity in Antiques,"] United States Environmental Protection Agency, www.epa.gov, accessed June 6, 2022.
Decaying radium also produces the gas [[radon]], recognized as the second leading cause of [[lung cancer]] in the United States and the United Kingdom.[https://web.archive.org/web/20210126012657/https://www.northampton.ac.uk/news/wwii-military-watches-potentially-pose-serious-cancer-risk/ "WWII Military Watches 'Potentially Pose Serious Cancer Risk,'] Faculty of Arts, Science, and Technology, University of Northampton, www.northampton.ac.uk/ June 14, 2018.
[https://web.archive.org/web/20210619061316/https://www.nrc.gov/materials/radium.html "Radium,"] United States Nuclear Regulatory Commission, www.nrc.gov/, June 19, 2021.

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