![]() Radiomir-The Radium’s Gone The Name Has Stuck This means that any radium dial found today is radioactive and will certainly set off a Geiger counter, because no watch is over 2,000 years old. The half-life for radium-1,602 years-is half the time it will take for it to completely decay. However, a dial with radium paint will continue to be radioactive, as radium literally takes millennia to completely decay, as it eventually ends up as a stable isotope of lead. Eventually, over years or even decades, radium paint will lose its glow, partly due to the deterioration of the phosphor. ![]() Furthermore, radium’s radiation breaks down zinc sulphide-used as a phosphor in radium paints-quite like UV rays from the sun chemically break down plastic and other synthetic substances. Additionally, radium decays to radon gas-a powerful carcinogen that causes death by cancer. With its emission of alpha particles and gamma rays, along with the beta particle emission of its decay by-products radium is highly unstable and is also a radiological hazard. Radium alone can create luminescence without an external light source, because of the energy from radiation emitted by radium particles in it. ![]() The phosphor commonly used in glow-in-the-dark substances used to be zinc sulphide, which is relatively safe by itself, but is highly problematic when used with radium or other radioactive substances as an activator or an ‘excitant’. For phosphorescence to take place, what’s required is a phosphor, and an ‘activator’ to enhance the absorption and release of photons. This re-emission-and glow-occurs over an elongated period of time, over a period of many hours, in the case of phosphorescent paints used for watch dials. Thus, phosphorescent materials absorb photons from external light, and then re-emit these photons as light that we see. Ultimately, it comes down to the atoms of the glowing substance, whose electrons absorb photons, and get excited to a higher energy state, and then emit photons when the material ‘relaxes’, which we can see as light. A photon is the quantum of an electromagnetic field, such as electromagnetic radiation from light and radio waves. The latter is the ability of a material to emit light after being exposed to an external source of light, due to the absorption of photons from the external source. When your watch hands glow in the dark, what you’re seeing is phosphorescence, which is a kind of photoluminescence. But what causes any substance in a watch to glow at all? For those who might not know or recall the physics of it, let’s just briefly go back to the basics. Or perhaps it was used too much, considering the harmful nature of the substances used for luminescence back in the day. Today, it’s possible to have a smattering of glowing parts in a watch, aside from the main markers and hands, but until a few decades ago, luminosity was a feature used quite judiciously. In the Autobahn, the speedometer motif on the dial is what shines bright, immediately elevating the automobile dashboard inspiration of the design with the luminosity. The former features a globe and a sky chart with constellations, which unexpectedly light up when held under a UV light, or in the dark, even though the lume in the hands is pretty obvious. ![]() ![]() From releases in recent years, the Girard-Perregaux Bridges Cosmos and the Nomos Autobahn come to mind. If there’s a special part of the display or an indication that features lume without it being apparent, it always comes as a wonderful little surprise when they shine their little UV light on it to showcase the glowing parts. You can instantly tell which parts of a watch will glow in the dark, owing to the apparent coating of Super-LumiNova or some other luminous material-or ‘lume’-generally on the indexes and hands. In all these years of wearing watches and seeing novelties at the watch fairs and manufactories, one aspect of the timepieces that always fascinates me-like I’m seeing it for the first time, every time-is the glow of the display. ![]()
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