More Info about Radioactive Glass

Issue 300 - April 1998

Webmaster's NOTE: This article consists of a letter sent to Lorraine Weinman, who was the Editor of the Crystal Ball at the time. It was a follow-up to Joseph Borque's article from the previous month. While normally we don't post letters to the Editor on the web site, the information in this letter is sufficiently important to warrant its inclusion. The last name of the writer was not given.

Dear Ms Weinman,

I do not often write letters to the editor but I thought Joe Bourque's article on radioactive glass in the February issue merited some comment.

There is an important misconception that Joe does not specifically deny. The misconception is that fluorescence and radioactivity are the same thing or at least related. The reason that this misconception has flourished is because uranium salts (usually oxide) have been the usual pigment for the yellow-green of "vaseline" glass and the fluorescence of dental porcelain. (I need to explain that a bit.) Uranium oxide is both radioactive and produces fluorescence. There are other radioactive elements which do NOT produce fluorescence, such as radium, thorium, plutonium, etc. There are elements which produce fluorescence but are NOT radioactive, such as zinc and most, if not all, of the rare earths.

I have been a member of NCC since Nov. 1981. I have been active in research in the materials used in dentistry since Jan. 1951. Among the products I have been involved with are plastic and porcelain replacement teeth. Both must be fluorescent because natural teeth are fluorescent. If you don't believe it, look in a mirror while you hold a UV light in front of your teeth: DON'T look at the light though, since some UV rays can damage your eyes.

The pigment to produce fluorescence in plastics has been, and still is, zinc oxide. Zinc oxide cannot be used in glass or ceramics because it loses its florescence at glass- or porcelain-making temperatures. Uranium oxide was used in porcelain teeth starting about a hundred years ago; before the dangers of radioactivity were known. In countries where International standards are effective, the use of uranium oxide was discontinued completely about 10 years ago, although some companies discontinued use of it about 35 years ago. The uranium oxide has been replaced with a rare earth oxide such as gadolinium.

In brief, if the color of a glass object is yellow to green and its fluorescence is what we call yellow-white, it is probably also radioactive because of uranium oxide. If the fluorescence is another color (natural teeth fluoresce blue-white), it is probably not radioactive.