What makes those stickers for children’s rooms, or painted on performers’ skin in theatre productions, actually glow? There are two sorts of glowing paint - the first, blacklight paint, is technically called fluorescent paint. The second type is phosphorescent paint. There’s a third – but we’ll come to that later.

The light side

Briefly explained, fluorescent paint absorbs invisible UV light, but then emits it again as visible light at a shorter wavelength, reflecting light back at you in a visible wavelength. You have probably seen blacklights in crime scenes, where lights emit UV ‘black’ light, which is invisible to the naked eye, but when it falls onto a fluorescent paint, it reflects brightly so you can see it. Therefore fluorescent paints work well in concert halls and dark rooms.

Phosphorescent paint works similarly but slightly differently. Rather than reflecting light back at you immediately, phosphorescent paint continues to reflect light back for a long time. It needs to be ‘charged up’, and daylight or turning on the lamp will be all it needs. When you charge up a phosphorescent paint, you expose it to UV and other light forms, and when in a dark room, it continues to emit the visible light for a long time. Regular fluorescent paint would appear dark, but phosphorescent paint appears visible as it emits reflected light. Nowadays, these paints are made using either zinc sulphide or strontium aluminate and are safe.

The dark side

But there used to be another type of glow-in-the-dark paint - radioluminescent paint – that has a rather dark and more sinister background.

This was invented in 1908 by Dr Sabin Arnold von Sochocky and it incorporated radium-226. His paint also used zinc sulphide phosphor, which degrades relatively fast and loses luminosity after a time, and clock faces and other devices painted with it do not retain their ‘glow’. But because of the long 160-year half-life of the Ra-226 isotope, they retain radioactivity, and this can be detected with a Geiger counter.

Radium paint was widely used for 40 years on the faces of watches, compasses, and aircraft instruments so they could be read in the dark, and Sochocky suggested in 1921 that, ‘…..in time every house would have a room lighted entirely by radium’. I don’t think so.

His company, The US Radium Corporation, extracted radium from carnotite ore for his paint, which was produced under the brand name 'Undark', and was a major supplier of radioluminescent watches to the military. They employed hundreds of workers, mainly women, to paint radium on watch faces and instruments.

During the ’20s and 30s, the harmful effects of this paint started to become clear. A famous case involved The Radium Girls, who were young women subjected to radiation exposure at the factory, five of whom gained notoriety for their efforts in challenging their employer in court.

After being told that the paint was harmless, they had ingested deadly amounts of radium after being instructed to ‘point’ their brushes on their lips in order to give them a fine tip, because using rags or a water rinse caused them to waste time and materials, but some had also painted their fingernails, faces and teeth with it, to surprise their boyfriends when the lights went out. Sadly, the five women all died from radiation exposure during the course of the litigation.

The rights of workers to sue for damages due to labour abuse was established as a result of this case – after which, industrial safety standards were enhanced, and led to the passing of a bill in 1949 which made compensation payable for all occupational diseases and increased the time for workers to discover and make claims for illnesses.

Shockingly, at the beginning of the 19th century, radium was used as an additive in products like toothpaste, hair creams and even food items!

The dial painters were some of the first victims of radioactive poisoning. Earlier, Marie Curie, who first discovered radium in 1898, had died from leukaemia - probably caused by her long exposure to radium, and Sochocky himself died from aplastic anaemia, also likely caused by radium exposure.

Author

Marilyn writes regularly for The Portugal News, and has lived in the Algarve for some years. A dog-lover, she has lived in Ireland, UK, Bermuda and the Isle of Man. 

Marilyn Sheridan