More info on Neodymium Glass
http://en.wikipedia.org/wiki/NeodymiumNeodymium glass (Nd:glass) is produced by the inclusion of neodymium oxide (Nd2O3) in the glass melt.
Usually in daylight or incandescent light neodymium glass appears lavender, but it appears pale blue under fluorescent lighting. Neodymium may be used to color glass in delicate shades ranging from pure violet through wine-red and warm gray.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.[13] Current sources include glassmakers in the Czech Republic, the United States, and China.
The sharp absorption bands of neodymium cause the glass color to change under different lighting conditions,
being reddish-purple under daylight or yellow incandescent light, but blue under white fluorescent lighting, or greenish under trichromatic lighting. This color-change phenomenon is highly prized by collectors.
In combination with gold or selenium, beautiful red colors result. Since neodymium coloration depends upon "forbidden" f-f transitions deep within the atom, there is relatively little influence on the color from the chemical environment, so the color is impervious to the thermal history of the glass. However, for the best color, iron-containing impurities need to be minimized in the silica used to make the glass. The same forbidden nature of the f-f transitions makes rare-earth colorants less intense than those provided by most d-transition elements, so more has to be used in a glass to achieve the desired color intensity. The original Moser recipe used about 5% of neodymium oxide in the glass melt, a sufficient quantity such that Moser referred to these as being "rare earth doped" glasses. Being a strong base, that level of neodymium would have affected the melting properties of the glass, and the lime content of the glass might have had to be adjusted accordingly.[14]
Neodymium compounds were first commercially used as a glass dye in 1927 and they remain a popular additive in glass. The color, due to the Nd(III) ion, is often a reddish-purple but changes with the type of lighting,
due to fluorescent effects.
The evolving technology, and improved purity of commercially available neodymium oxide, was reflected in the appearance of neodymium glass that resides in collections today. Early neodymium glasses made in the 1930s have a more reddish or orange tinge than modern versions which are more cleanly purple, due to the difficulties in removing the last traces of praseodymium in the era when fractional crystallization technology had to be relied on.
[13] "Chameleon Glass Changes Color".
http://coloradosprings.yourhub.com/CrippleCreekTellerCounty/Stories/Arts/Story~443258.aspx. Retrieved 2009-06-06. [dead link]
[14] Charles Bray (2001). Dictionary of glass: materials and techniques. University of Pennsylvania Press. p. 102. ISBN 081223619X.
http://books.google.com/?id=KbZkxDyeG18C&pg=PA102.
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