It all started back in the 1999 - 2000 time frame. My younger daughter was living in Indianapolis at the time. We (her dad and I) had gone down to visit, and made a day of shopping the sprawling antique shops in the area. We came upon a glass case with quite a few nice pieces displayed. There was a small green item, perhaps a candle holder, that my daughter bought for me.
But I could not take my eyes away from a small lavender vase. I never saw lavender like that. It had no sheen, no rainbows, or other enhancements you normally see in glass. No, this had a life of its own. It was lavender that hinted that it wanted to be pink and blue at the same time, like a living color inside of it. I was so taken by the color my daughter bought it for me.
My vase lived on a window shelf, so I could enjoy it in the light. It was always more pink in the sunlight. I didn't think much about it. Then one night I noticed it lost its color! All traces of lavender and pink were gone! It was just a dull, pale, lifeless blue. I was shocked and saddened. How could that be? How could color "leach" out of glass? It was not possible, but yet, here I was, holding my beloved lavender-pink vase that had gone dull blue. With a downcast heart I returned it to the shelf.
The next morning the pink was back!
So now I had a mystery. That evening I looked and again saw my vase had paled to blue. I took it off the shelf and held it under the kitchen light....ahhhhh, the kitchen light. I had recently changed bulbs to curly fluorescent! I still had some incandescent bulbs, so I took my vase over to one of those lights. The pink returned! I began searching the internet for answers. Oddly, none could be found, so I gave up.
I stumbled upon the answer a week ago. I was reading an article about dichroic glass, which changes color depending on how light sines through it. I took the "changing color" part as a clue, so I searched, and stumbled upon Alexandrite or Neodymium glass. FINALLY I had an answer!
Alexandrite is vintage but not antique. Neodymium was discovered in 1885 and first used as a glass dye in 1927. Several different companies produced it, each with their own slightly different chemical formula. You can Google it to read more if you are interested, but basically Neodymium absorbs certain lightwaves so it appears to change color under different lighting. Neodymium - Wiki
Here are some pictures that demonstrate the dynamics of this glass.
Incandescent (old-style light bulb)
As you can see, the vase on the left is aqua under fluorescent lighting. Different glass companies used different formulas, which gives the variety in color.