A key aspect of a tool watch is it’s legibility. For daytime use, maximum legibility is achieved by using high-contrast dial designs that incorporate bold and easily discernible shapes and anti-reflective coated crystals.
If done well, their effective utility is enhanced during low-light and nighttime situations.
The history of luminous painted dials started with the discovery of Radium by Marie Curie and her husband Pierre in 1898. It was quickly recognised for its ability to emit energy in the form of light in a continuous manner. The onset of the First World War would prove the perfect proving ground for the technology.
Widely adopted in the manufacture of watches, clocks and cockpit instruments of World War I, this industrial-scale use of Radium did not come without a cost. In the early days of its application, it was not widely known that Radium was a highly hazardous radioactive material.
Even after the negative effects of Radium were established, some dial companies, in their drive to keep up with the output requirements of war, continued to downplay the dangers of exposure to the women who painted the lume onto the dial markers and hands. Many of these ‘Radium Girls’ would suffer fatal radiation exposure, and the quality of life of those who lived would be greatly compromised. Eventually, there would be a successful legal action, a faint silver lining in a very dark corner at the nexus of two of the prime drivers of horology: war and science.
Today, Radium is banned in the production of watch dials, but is still present on many vintage watches. If you hold a Geiger Counter next to an old Rolex or field watch from the 1950s, it will start tick, tick, ticking away!
Other paints were also tried as substitutes. Promethium, and later Tritium, were found to be good low-energy emitters. Tritium is a radioactive form of Hydrogen, and with a half-life of 12.32 years, it made for the ideal substance for use in watches and other instruments including cockpit dials and gunsights.
A few brands that are well known for using Tritium are Ball, Marathon, Traser and Luminox, though exposure is managed by encasing the gas in micro tubes made by the Swiss company MB Microtech.
A third paint substitute for radium that was invented in 1993 is Luminova. In 1998, two companies (Nemoto & Co. and RC-Tritec) joined forces to cater for the Swiss watch market. This was a substance that did not contain any radioactive excitants at all, making it the standard for the dial-making industry. The core ingredient of Super-LumiNova is Strontium Aluminate, an extremely effective phosphor. Combined with Europium, it creates a chemical reaction that once charged with light, will glow very brightly to start with, and then diminish in intensity for several hours thereafter.
Super-LumiNova comes in a variety of colours, and typically glows green or blue. C3 is the brightest glowing variant while, until recently, BGW9 had the longest-lasting glow. An improved version of C3 called X1-C3 has since taken the lead on both brightness and length of glow.
There are other brands of luminous paint out on the market. Seiko (Lumibrite), Rolex (Chromalight) and Omega all have their own formula, but (obviously) do not make them available for third parties.
Super-LumiNova is considered the best readily available luminous paint on the market. In many cases, it outperforms the luminous paint of some of the big brands. Just do a search for ‘Lume Wars’ on Youtube and you’ll find many comparison videos of glowing dials from different brands.
Note that some brands that have their dials manufactured in China claim that they use C3 or BGW9, but if it does not say Swiss Super-LumiNova, it probably isn’t. These days, watch companies, including us at Draken have gotten really creative with the use of luminous paint. There are a number of ways it can be applied to a dial. Thicker application is best, though the marginal improvement in glow does drop off at about 10 layers.
This is the more traditional application of lume, where the paint is applied directly to a typically dark background dial. To get a really bright glowing printed dial, it needs to be layered between 8-10 times as seen on our Aoraki model.
Often watches will have hollow or cup-shaped indices that form a vessel for the luminous paint. This technique is great as you can easily ‘fill’ the indices, thereby maximising the brightness. Our Tugela GMT used this method to great effect.
This is a double-layered dial with the bottom layer having the lume applied thickly and the top layer having cut-outs for the lume to shine through. Our Benguela model employed this technique and introduced some applied bead-blasted indices which overhang the cut-outs.
Full lume dials
Reversing the use of the lume so that the entire dial glows while the indices remain dark is called full lume. Again, to achieve a really good quality full lume dial, the paint needs to be applied in layers (ideally 10 or more). An example of full lume dial is the Kruger Panda and White.
A newer method of applying lume to dials is called Lumicast. Instead of being pressed onto the dial in liquid form via pad transfer or silkscreen, the shapes are 3D moulded separately as ceramic parts. This results in a brighter and longer glow than seen in applied indices. We are excited about this new Super-LumiNova technology and are thinking about how we can use this in a future project!
This brings us to the end of our series on ‘5 Things to Know Before You Buy a Tool Watch’. As I said at the beginning, watch collecting is a rabbit hole. Hopefully, now that you know a bit about what makes for a good quality timepiece, you’ll be a bit more like the rabbit, and less like Alice.