History of Luminescent Paint on Watches

“How good is the lume?” – a question we often hear in reviews of modern timepieces. Luminescent paint, a.k.a. “lume,” has become increasingly important for watch enthusiasts and collectors. Good application of lume on a watch is a sign of quality, and there are only a few types of lume that watch brands can choose from. What makes a good application of lume, therefore, is how much of it there is, not necessarily what compound is applied on the dial. However, there are certain lumes that glow better and for longer than others. All this to say: luminescent paint is important for many; it felt fitting to talk about it today. First, we’re going to discuss the history of luminescent paint, then the primary types that exist, and finish with a few nerdy tidbits. 

Source: www.keepthetime.com

History of Luminescent Paint: Radioactive Compounds 

Before we get started, it’s important to make the distinction between self-induced and induced luminescent materials, where the best example of the former is radioactive materials (i.e. Radium and Tritium) and the best example of the latter is SuperLuminova. Nowadays, most watchmakers use induced luminescent paints, all of which come more or less from the same compound but are marketed under different names. (More on that later.) 

Source: www.youarrived.com

The first radioactive luminescent paint was invented in 1908 and was made of Radium. This material was used a lot at first because it can glow for 1,600 years and is self-induced, meaning it doesn’t mean to be exposed to a light source in order to glow. Radium lume glows all the time: day and night. While the wearer would be protected from the low-emission radiations coming from the dial thanks to the case and crystal, it was the watchmakers that were at a greater risk via direct exposure to the material when building and servicing the watch. For that reason, Radium-based lume ceased to be used in 1968. 

Source: www.bachmann-scher.de

A safer but not radioactive-free material called Promethium was used alongside Radium and phased out at about the same time. Though it was safer, Promethium would only glow for 2.5 years on average which meant it had to be reapplied on a regular basis. This is when watchmakers started using Tritium which was also safer than Radium and had a better glow life of about 12 years. At first, Tritium was painted directly on the dials like it was the case for Radium and Promethium. However, over time, the material will seep through the dial and damage it. Although Tritium was largely abandoned in the 1990s, some brands still use it today but in a different form: they put it in tiny glass tubes, making it more condensed, safer, and giving it a glow life of about 25 years. 

P.S. I don’t know if “glow life” is an actual thing to say, I just made it up as it seemed more fitting than “shelf life.” 

Source: www.teddybaldassarre.com

History of Luminescent Paint: Non-Radioactive Compounds 

It was therefore about time to move onto a non-radioactive material and the jump was made possible thanks to a Japanese scientist named Kenzo Nemoto. His career started in 1941 when he opened a shop to sell luminescent paint. He was commissioned by the Japanese Government to provide paint that could be used on the gauges of airplanes during World War II. Shortly after the war, Nemoto started working on a non-radioactive compound and, in 1962, created a new phosphorescent material made of strontium aluminate. Unlike radioactive materials, strontium aluminate doesn’t decay over time. Furthermore, while Radium and Tritium were self-induced compounds, Nemoto’s creation has an induced luminescence, meaning it needs to be charged by a light source in order to glow. 

To make a long corporate story short, what Nemoto created came to be known as LumiNova after being joined by RC-Tritec AG, a Swiss manufacturer of Tritium luminescent paint founded in 1993. The latter started selling Nemoto’s phosphorescent material under the name SuperLuminova on the Swiss market, a name that we all refer to now when speaking about lume.  

Source: www.prestigetime.com

Nerdy Tidbits About Luminescent Paint 

What is called SuperLuminova, Rolex’s Chromalight, Time’x Indiglo, and Seiko’s LumaBrite, are in fact all the same thing but marketed under different names. Though Seiko’s LumiBrite is known to be one of the best lume on the market, something that is related to how the brand applies the lume, not what it is made of. The same can be said of Chromalight which is also known for glowing brighter and longer than most currently available SuperLuminova blends. It seems Rolex has a way of making the compound and applying it that is different from how most watchmakers do. Unfortunately, I do not have any insider information about Rolex’s processes. 

Source: www.luxurylondon.co.uk

Furthermore, SuperLuminova has created different colored lumes to be used on different styles of watches. This means the compound itself has been modified—again, I wouldn’t know how they do it—and each blend comes with different levels of brightness and longevity. Of the dozen blends currently available, we most often hear of C3, BGW9, and C1. C3 comes with a cream color and glows green and is known as being the brightest of all. While BGW9 has a white color and glows blue, and although it doesn’t glow as bright as C3, it lasts longer. C1, for its part, also appears white when not charged and glows blue in dark conditions, but doesn’t merely glow as bright as C3 and BGW9. 

Source: www.snglrtywatch.com

Final Thoughts 

As mentioned in the introduction, many of us watch collectors and enthusiasts are obsessed with lume. What blend is it? How much of it has been applied, 3 layers or 7 layers? Which brand creates the best lume? What about fully-lumed dials? We can discuss lume in many ways and we all have our preferences. In this article I attempted to provide some context as to the origin of luminescent paint and how it’s been used today. I would be curious to know if you are a lume nut as well? Please share your thoughts in the comments section below.