Topic: Alexandrite Bird Bowl, Why green?

[Frank]

Wow, that device seems easy to make and could cause something of a revolution for glass collectors with the patience to analyse such things! It gives a cheap and easy, dependant of the object, to at least match glass mixes and add to the armoury of identification tools!

[Martin Brown]

The good news it that you don't need anything quite so sophisticated for a quick spectral ID. A humble aluminised scrap CD in sunlight will do to produce a low resolution reflection spectrum - you can get quite high resolution at glancing incidence as this website describes.

http://home.freeuk.com/m.gavin/solaspec.htm

Nd glass is somewhat unusual in showing so much structure in its visible light spectrum.

I had a quick try with a swatch of theatrical light filters and the only one that has a sharp enough edge to give a moderately sensitive test for Nd doped glass is LEE filters 779 "bastard pink" (sorry about the name I didn't choose it). The filter looks mostly orange, but Nd doped glass looks almost magenta through it. Yellow indicator LEDs on phones etc are also significantly dimmed by Nd glass. You can adapt a cheap $1 3v torch to use a yellow or amber led and a 100ohm resistor with ease - some work better than others. Hope this helps.

Best regards,
Martin