What is Tritium Lume?

Jul 25, 2018

What is up, watchfam?! Today, we’re going to take a look at one of the oldest kinds of luminescent material found on watches – tritium.

Long before Superluminova, or Seiko’s classic Lumi-Brite, most watchmakers were using something called tritium on the dials and hands of their watches to give them glow in the dark properties. It wasn’t the first kind of lume, though – that honor goes to a compound called radium which has its own interesting, somewhat tragic history that is worthy of its own article. As a result, radium was effectively outlawed in 1968, and tritium became the luminescent material of choice.

Ball Engineer II featuring Tritium Gas Tubes
Source: GearPatrol

Tritium maintained a lot of the same chemical properties as radium, but at a significantly less radioactive level (not to say it wasn’t radioactive, because it was, but while both tritium and radium were never harmful to the wearer, tritium was also safe for the manufacturer). Generally, tritium is considered to be about as radioactive as an x-ray, and this decrease in radioactivity comes from a decrease in the strength and quantity of the beta waves that are given off by tritium as an element. As such, it maintained the constant glow of radium (caused by the decay of the paint’s compounds which would release electrons that would, effectively, glow), but as a much safer alternative.

Tritium and radium alike suffered one fatal flaw, aside from the whole radioactivity thing – they were in a constant state of decay as they continued to glow. As such, after time, the lume would glow duller and duller and, eventually, cease glowing altogether. As this happened, the lume would also take on a sort of creamy and, eventually, sand-colored appearance, as seen below.

An early Rolex ref. 6538 w/ patina tritium dial
Source: Rolex Passion Report

Tritium remained the lume of choice until right around the late 1990s to early 2000s, at which point it was replaced by the far safer (read: not radioactive) Luminova and, eventually, Superluminova. Tritium isn’t totally dead, though. Some brands, such as Deep Blue and Ball use small gas tubes filled with tritium gas to achieve the same degree of constant brightness that doesn’t need charging as the paint of old, but with the added bonus of being replaceable when they reach the end of their life.

If you’d like to see articles discussing the other major kinds of lume throughout history, email us at info@theoandharris.com and definitely let us know!! And until next time – keep it classy, watchfam.