Google. Is there anything it can't teach us? You see, I had never heard of Uranium Glass until recently, and it was after searching Google for the Periodic Table of the Elements that I became aware of its existence. My housemate and I are comparing a modern Periodic Table, and an early Greek table with 20 entries, seeing what they got wrong in those early days, what was close, what was way off. It was then that my other housemate pointed out that no matter what you look up on Google, it always seems to have a link to eBay.
Now searching eBay for a Periodic Table is rather boring, so we took the search to another level, by searching Google for uranium. Sure enough, there's the link - Shop at the World's Online Marketplace. Great value & range. www.ebay.com.au. Naturally, we decided to find out just who was selling uranium through eBay, expecting to be taken to anything with uranium in its name, while not being remotely related to actual uranium.
What we ended up finding, was Uranium Glass.
So just what is Uranium Glass? A fancy name for something not remotely related to uranium? A strange marketing ploy? In fact, Uranium Glass is exactly what the name suggests - it is glass, containing uranium dioxide (uranium salts), and yes - it is radioactive. A geiger counter will register a reading from Uranium Glass - however the level of radiation is only just above the level we are exposed to in everyday life, so is not considered harmful.
So just why did somebody decide to mix uranium dioxide with glass?
It's all about the colour. Uranium dioxide mixed into glass, results in a yellow-green coloured glass. It is generally accepted that it was first produced by Josef Riedel, one of a long family line of glassmakers in Bohemia. In short, it contains approximately 2% uranium dioxide, producing its distinctive colour. While the colour may have been distinctive at the time uranium glass was first produced, it doesn't compare to the colours available using modern glass working techniques - however it is still prized by collectors worldwide. The reason for this is more than simply the curiosity value of owning an item containing uranium - rather, it is something that I am sure the creators of this glass could not have imagined.
Placed in a position with ultraviolet backlighting, Uranium Glass glows bright green. The difference is remarkable, the glass item going from being a yellowish-green - quite a muted and dirty looking colour - to a vivid, fluorescent colour. The electrons in the uranium are excited by the exposure to ultraviolet light, and enter a high energy state. In order to return to a low energy state, photons are released, resulting in the distinctive green glow of uranium glass. Collectors the world around meet to display their collections, shown under ultraviolet light.
Uranium glass is also known as 'Vaseline glass', however there are distinctions between uranium glass and vaseline glass. Unfortunately, this distinction is by no means universal, and definitions vary. What may be called uranium glass is Australia, may be called vaseline glass in the United States. Some glass produced with heat sensitive chemicals turn a milky white colour towards the edges - similar to the colour of vaseline - and this is referred to as vaseline glass in some places. Some collectors are members of organisations, who have stated the distinction between vaseline glass and uranium glass as far as their organisation is concerned - Vaseline Glass Collectors Inc. use two simple rules to define vaseline glass - it must be yellow first, and glow green under a ultraviolet backlight second. Obviously, this definition is quite different to the definition of vaseline glass as far as many other collectors are concerned. With so much disagreement amongst collectors and organisations, I'm not going to attempt to provide a definitive distinction - I doubt one will ever exist. For the sake of simplicity, I'm using the term uranium glass in this writeup.
The bulk of the uranium glass in existence today was produced from the 1830's to the 1940's. As uranium was a component of the atomic bomb, wartime governments were eager to restrict access to it. There were also concerns regarding the health of glassworkers exposed to uranium during the glassmaking process. In the 1950's, these restrictions were relaxed, however there are few places producing uranium glass to this day. In addition to the cost of uranium, health and safety regulations measures to protect workers against harmful exposure to radiation have made the manufacturing process expensive. These days, most uranium glass is sold by collectors.
There are several web sites displaying pictures of uranium glass, in its normal form, and as it appears under ultraviolet light. The difference needs to be seen to be believed - these links will take you to some good examples (please inform me of dead links):