There are several elements that will cause common glasses to fluoresce under ultra violet light. The fluorescent response depends on several factors: primarily the elements present, sometimes matrix, the concentrations, the wavelength of the exciting radiation, the intensity of the exciting radiation, colorants, etc.

The type of Ultraviolet light and the color of visible light is determined by its wavelength. The unit of measurement for light wavelengths is the nanometer (nm). Ultraviolet light is generally considered to be from 200 nm to 400 nm.

Click Here to learn about 395nm vs. 365nm Lights

Uranium (395nm & 365nm)

Uranium glass is as a blanket term used for any glass containing uranium. It is characterized by the presence of uranium (oxide) and, in some cases, iron oxide.

Unlike the commonly known (green) uranium glass, vaseline glass is a type of uranium glass — referring specifically to the bright lime-yellow (canary) color. Uranium can also be found in some custard glass, Burmese glass, milk glass, jadeite, and opaline glass. It is also (scarcely) seen in blue glass, pink glass or other obscure colors.

Uranium Ghost Glowers: For every rule there is an exception. While nearly all uranium glass will glow brightly under 395nm UV light every once in a while you may come across a piece that really only seems to react under 365nm. Macbeth Evans was one of the most notable glass makers to produce these “ghostly glowers”. But, this is where is gets tricky! Because manganese also fluoresces under a 365nm light, the only way to positively confirm if something is Uranium Milk Glass is to test is with a geiger counter.

Uranium glass can register above background radiation on a sufficiently sensitive Geiger counter, although most pieces of uranium glass are considered to be harmless and only negligibly radioactive. Most uranium glass contains less than a 2% uranium content, however some pieces from the early 1900s can contain up to 25%.

After World War II, using depleted uranium (DU) became more common than using natural uranium ore. DU comes with the benefit of mostly releasing alpha radiation, which can’t penetrate the skin, so it is not considered a serious hazard outside of the body. Collecting Uranium Glass accounts for approximately 1 to 2% of the average American’s annual radiation exposure. In fact, a report published by the US Nuclear Regulatory Commission in 2001 stated that uranium glass is considered to be safer than household electronics.

While it is completely safe to have and display uranium glass in your home, some people recommend not eating or drinking from it as you can accidentally ingest small fragments of radioactive glass.

These specific items should be notably avoided for their original intended use:
Uranium glass citrus juicers, as the acid can etch into the glass and leach out potentially harmful radiation.
Uranium glass knives, as they’re prone to chipping off glass into food while cutting.

Less Common Colors of Uranium Glass:

Uranium Glazed Ceramics (365nm / 254nm)

Uranium glass is characterized by the presence of uranium (oxide) and, in some cases, iron oxide. Uranium glazed ceramics can register above background radiation on a sufficiently sensitive Geiger counter. “Radioactive Red” Ceramics are known to be especially “spicy” with high readings on a Geiger counter.

The use of uranium in ceramic glazes ceased during World War II when all uranium was diverted to the Manhattan project and didn't resume until 1959. In 1987, NCRP Report 95 indicated that no manufacturers were using uranium-glaze in dinnerware.

Before the 1970s, many companies used radionuclides to color glazes. The most commonly used radionuclides were uranium, thorium, and potassium. These elements emit alpha, beta and/or gamma radiation – These glazes can be found on floor and wall tiles, pottery, and other ceramics. Uranium was used in the glazes on Cloisonné jewelry to make orange, yellow and green colors. Some Fiestaware produced before 1973 used depleted uranium to create the color of the glaze.

* The U.S. Environmental Protection Agency warns consumers not to use radioactive glazed ceramics for food or drink use, the glaze can leach Uranium and heavy metal into your food (Especially if acidic)

Cadmium & Selenium Glass (395nm & 365nm)

Cadmium Sulphides are associated with making yellow glass and this causes it to glow yellow under UV light. When used in conjunction with Selenium or Sulphur it yields shades of yellow, red and orange glass — resulting in it fluorescing yellow, orange, pink or red under UV light.

*Cadmium is toxic and items containing cadmium should only be used for display, do not eat or drink from cadmium glass.

Selenium Glass (395nm & 365nm)

Selenium was responsible for making glass pink and red and when used together with Cadmium Sulphide an even more brilliant red was created known as Selenium Ruby. Selenium can be found in pink, red and ruby colored glass and fluoresces – some, but not all, glow an intense pink under UV light.

Neodymium Glass (365nm / 395nm)

Neodymium glass (sometimes referred to as Alexandrite glass), changes color according to different lighting conditions. The glass appears lilac (or sometimes pink) in natural sunlight or yellow incandescent light, and smoky blue in fluorescent/white light. This is due to the presence of Neodymium oxide within the glass.

On its own, Neodymium is not UV Reactive. Some manufacturers added Selenium into their glass matrix which resulted in the bright pink fluorescent glow under UV light, seen more commonly in Neodymium Glass. Neodymium glass has also been noted to fluoresce a vibrant to dull pink, pale green, or a peachy-orange color depending on the matrix of chemical additives and concentration of those chemical additives — Some pieces require 365nm while others fluoresce beautifully under a 395nm light.

The first commercial use of purified neodymium was in glass coloration, starting with experiments by Leo Moser in November 1927. The resulting "Alexandrite" glass remains a signature color of the Moser glassworks to this day. Neodymium glass was widely emulated in the early 1930s by American glasshouses, most notably Heisey, Fostoria (Wisteria), Cambridge (Heatherbloom), and Steuben (Wisteria), and elsewhere (e.g. Lalique, in France, or Murano). Tiffin's ‘Twilight’ remained in production from about 1950 to 1980. Current sources of production include glassmakers in the Czech Republic, the United States, and China.

Manganese Glass (365nm)

Manganese is one of the oldest glass additives and was used in small quantities to de-colorize (remove the green tint from glass to make clear) and in higher contents to colorize glass. Manganese can be found in nearly all colors of glass, especially amethyst and turquoise blue glass. Manganese fluoresces green under 365nm UV light, often being confused with Uranium.

High Content Manganese Glass: For every rule there is an exception. While most glass that contains manganese will not fluoresce under a 395nm UV light, some pieces contain a particularly high manganese content which will react under 395nm. Do not be fooled into mistaking this for Uranium Glass, it is not, and can be distinguished by the lack of radioactivity (when tested with a geiger counter) and the subtle differences in color.

Lead Glass (365nm)

High-lead glasses are usually colorless. Under a 365nm light the fluorescence becomes noticeable at a level of about +24%. However lower lead content also fluoresces with a short-wave (254nm) light. (Don't mistake the reflection of visible purple light from the UV light for Lead fluorescence.

*Though occasionally drinking out of lead glasses may not be the end of the world, the FDA warns that having lead-contaminated glasses within children’s reach at home can result in dangerous exposures. This glassware also poses greater danger to pregnant women, the FDA says.

Boron Nitride (395nm & 365nm)

Boron Nitride is a mold release agent that sometimes reacts with chemicals in (Ruby / Red) glass which makes them UV Reactive. This is sometimes confused with cadmium glass because it fluoresces a similar yellow-green color.

Cadmium Glass vs. Boron Nitride: Be sure not to confuse the fluorescence of cadmium glass with that of boron nitride. The easiest way to tell is by the color difference. Boron Nitride will fluoresce yellow-green under UV light, while Cadmium fluoresces yellow-orange.

Radium Paint (395nm & 365nm)

The first material applied to watch dials for nighttime luminescence was radium paint, which, thanks to radium’s half-life of 1,600 years, offered a long-lasting glow during that period before dimming — the catch being that, as its name implies, radium (specifically Radium-226) is radioactive. In the 1920s, the mostly female factory workers that painted the watch dials with radium compounds started falling ill and dying at alarming rates, leading to lawsuits against the companies that produced the material and eventually, safer working conditions and an abandonment of radium as a luminous substance in watchmaking by the 1960s.

Replacing radium for a short time as the luminous substance on watch dials was a compound called Promethium (Pm-147), which was less radioactive but had a half-life of only two-and-a-half years and thus a much shorter period of luminescence. Next up was Tritium H-3

Tritium Paint (395nm & 365nm)

Tritium H-3 is a radioactive isotope of hydrogen with a respectable half-life of 12.3 years and, as a low-energy beta emitter, far less hazardous to work with than radium. Tritium was not entirely without risk, however. Used on surfaces like dials, tritium had a tendency to diffuse, seeping through the case and into the skin of a wearer. Tritium-based paints on dials, which were used by numerous watch brands, including Rolex, were banned in 1998.

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