Imagine, you are living in the early 1900s. You are very lucky today, because your husband has given you a beautiful new sugar bowl. He dropped the last one and it smashed, so you are pleased to have a new one. This one is a beautiful clear green glass, with delicate cut glass designs on it. This vaseline glass is so pretty and delicate, and you just love it. It does have a few odd qualities, like the occasional glow, but that isn't anything to worry about.
When I took these Uranium Glass (also known as vaseline glass) slag pieces and buttons to show the children they were at once fascinated and horrified. Children are always interested in the unexpected and when I showed them how this glass glows green under a certain type of light, they were impressed and intrigued. They were also impressed by how 'pretty' the glass was, even when it wasn't glowing. The children did wonder why the glass glowed though and when I explained to them that it contained tiny amounts of uranium (and so was ever so slightly radioactive) they were quite disturbed. They've heard a lot about radioactivity and its dangers after the Japanese Tsunami, so were well aware of why radioactive material is 'bad'. They trust me, and so were reassured when I told them it wouldn't hurt them, but the idea of adding radioactive material to glass was just "too bizzare" (uranium glass does give off radiation, but only very low levels, and is safe if used in a 'normal' way. If you have a piece, don't sand or grind it). They were particularly disturbed when they discovered that this type of glass was used to make dishes for food, and even jewellery.
We can't be completely certain when uranium started to be added to glass, though we are pretty certain it was in the 1830s. There is some speculation that the Romans knew about uranium glass, as a Roman mosaic from about 79AD was discovered in 1912 near Naples which appears to contain uranium glass. This may have just been an accident though. We do know though that in the 1830s people were specifically starting to add uranium to glass as a colouring agent. Josef Reidel may have been experimenting with uranium in his Bohemian Glassworks in the 1830s and we know that Whitefriars Glassworks were experimenting with uranium in 1835, giving a pair of uranium glass candlesticks to the Queen in 1836.
Uranium salts are a very vivid yellow, and so when added to glass colour it yellow. If green is also added, the colour becomes a vivid green (one of the most common colours). Other colours like blue and pink or even white can also be found in uranium glass, created by adding other colours to the mix. This colouring may have been why uranium was added to glass in the first place, but it isn't the main reason why people collect it today. People who collect uranium glass today usually collect it for its amazing bright green glow under black (UV) light. Why does it glow though? When UV light hits the glass, it excites the outer electrons of the uranium, emiting energy which we see as a green glow, or green light. This process is called florescence. If you would like to learn more about Uranium Glass, or see other examples of it, click here.
