Thorium is an element that can be found in small amounts in rocks and soils. It was first discovered in 1928 by Swedish chemist Jöns Jacob Berzelius, who named it after Thor, the Norse God of Thunder. Thorium dioxide is added to silica mixtures to create glass with high refraction and low wavelength dispersion, which is ideal for lenses used in optics as it eliminates chromatic aberrations in a single element, reducing the need for a second element to correct those aberrations.

Thorium is a radioactive material, which means that its atoms' unstable nuclei release energy by radiation. The length of time for an atom to decay is called the element's half-life, and thorium has a half-life estimated to be over 14 billion years, making it still radioactive, though low on the radioactive scale. Over time, thoriated lenses will develop a yellow-brown patina, compromising the image in both the color and light transmission.

Yes, prolonged exposure to UV light can reverse the yellowing of thoriated lenses. UV light detaches the bond of zinc oxide and returns it to its original state within the glass, removing the yellowing.

Thoriated lenses have been extensively researched, and while they are still radioactive, they are considered safe to use. However, it's understandable that some people may not feel comfortable using them, and there are plenty of non-radioactive lenses available.

The use of radioactive elements in lenses began in the 1940s and continued through the 1970s. By the late 1970s, however, concerns about the potential health risks associated with these lenses led to a reduction in their use. In the early 1980s, manufacturers largely stopped using radioactive elements in their lenses altogether.

No, not all vintage lenses are radioactive. The use of radioactive elements in lenses was primarily limited to a specific time period in the mid-20th century, and not all lenses from that time period were radioactive. Additionally, there were some lenses produced outside of this time period that were radioactive, so it is important to research specific lenses to determine if they contain any radioactive elements.

Although the radioactive properties of thorium lenses may sound concerning, research shows that they are safe to use. However, if it still makes you uncomfortable, there are plenty of non-radioactive lenses to enjoy. As with any technology, there are pros and cons to using thorium lenses. The high refractive index and simplified optical design of these lenses made them a game-changer in the past, but the color cast they produce over time may not be for everyone. Nevertheless, it is interesting to see how science and technology have evolved over time, and thorium lenses are a fascinating example of this.