Topic: weird UV glow color and pattern on cased Harrach pitcher = Cadmium sulphide

[Glen]

Kristi - the article (updated link below) was about vaseline, and in it the question was posed; "what causes an orange glow?" I spoke to John Boyd (at Boyd Art Glass) and he gave me the following answer (which is also in the article).

"there are several metal oxides that fluoresce. The only one that comes to mind that will flouresce orange in glass is Cadmium Sulfide. It is the only colorant that will make glass yellow. Actually, cadmium is one of the colorants that "needs" a reducing flame. But to help it to the brown side (topaz) I think I would add a pinch of blue, black Copper Oxide." (thanks to John Boyd for the info).

http://www.carnivalglass.org/newbies/10.asp  for the updated link.

And to Anne.....thank you  (especially for pointing out my gender    )

Glen

[krsilber]

Thanks, Glen!  So looks like cadmium sulphide is the culprit.  I wonder if he meant it's the only fluorescent colorant that's used for yellow (but even that's not true, since there's uranium), since there are yellow glasses that don't contain it.

Still a bit of a mystery what created the pattern of glowing in mine.  Suggests that not all cadmium sulphide-containing glass will glow.  Boyd's comment that it needs a reducing flame just confuses things more because it suggests that for yellow it needs to be of a certain valency, and my hypothesis was that on the pitchers it's not all of the same valency.  Hmmm.

[Cathy B]

Kristi, what is the pattern of glowing on your pitcher? If it had cadmium sulphide of a different valence, what would have caused that? Different batch?

Speaking of glowing orange glass, has anyone looked at Davidson orange cloud under blacklight? The clouds glow the most magnificent orange. Does anyone know the composition? (Is it in Chris' book?)

[krsilber]

You can sort of see the pattern in the top photo in my first post.  The brightest orange is at the top, from the spout to about 2" (~5 cm) down the neck.  The bottom also glows brightly, but fades gradually above an inch or two from the bottom.  The second one is basically the same, but the orange areas are larger.  ...Just took a photo of the two together, so you can see.  Also another photo of the first, where you can sort of see the green tint that shows up between the orange parts.

My guess is that the change is heat-related.  I don't know, maybe it's not a valence thing, maybe it's that a new compound is formed.  Perhaps in those areas the layers not only fused, but mixed?  I wish I knew more chemistry.  But at any rate I can't figure out any mechanism besides heat that would cause the pattern they have.

How about this scenario?  Parison blown into mold, removed, reheated so that the punty can be applied, neck is reheated for shaping...you've got struck UV reactive colors.

The Davidson thing sounds cool!  You guys talk about these makers, Davidson and Sowerby and others, and I am absolutely clueless.  There's a lot of British glass that apparently never hit our shores...or I'm simply clueless.

[Cathy B]

I see what you mean - it is strange, isn't it. Can you see any corresponding colour difference under normal light? If that's the mechanism, presumably it was 'struck'* when the pitcher was reheated to form the lip at the top?  :huh:

More research into CdS needed! Fenton apparently used cadmium sulphide and selenium in their amberina (under Amberina here. I'm a complete dunce on chemistry, so someone else might have to help! I've just read the Wikipaedia entry on valencies and it pretty much went straight over my head.  :chky:

*(Just to define this for anyone reading in the future, as far as I understand it, when a glass vessel has sections reheated to force a chemical reaction which changes the colour, the colour is said to have been 'struck'. Clarification/correction welcomed as always )

[Glen]

I've written here a couple of times about amberina / red and the weird glow it has. Summit's Geraldine's Delight (opaque-ish orangey/yellow/red) is another colour that has that odd orange glow. Here's something I wrote a couple of years back.

'Vaseline' or Uranium - or what?
« Reply #5 on: August 17, 2005, 09:20:36 PM »

Some glass may have an orange glow under UV light. The main coloring agent that causes this is cadmium, usually in the form of cadmium sulphide. The fluorescence can vary from a citron yellow through to a dark red. Cadmium was often added to the batch along with selenium to create red glass. You may note how the amberina sections of amberina/red glass glow. Why? Red glass is re-heated to strike the color—until the moment of striking the selenium/cadmium red glass will react with UV light and glow. But as soon as the red color appears, the fluorescence vanishes.

Glen

[krsilber]

"Can you see any corresponding colour difference under normal light? If that's the mechanism, presumably it was 'struck'* when the pitcher was reheated to form the lip at the top?"

No, I can't discern any obvious difference under normal light.  The tone and depth of the yellow seems uniform. The bottom may be just slightly paler, but the difference doesn't conform to the pattern of UV reactivity.  And, yes, that was my hypothesis about it being struck (incidentally) at the top to form the upper neck and lip.

...But now, after reading Glen's post, that wouldn't seem to make sense, if in striking a piece for amberina the effect disappears.  But then again, things are complicated by the presence of selenium (and whatever else is in there!).  I was surprised to see that a modern company like Summit used cadmium, since it's known to be extrememly toxic.

Glass color chemistry "strikes" me as quite complex...and fascinating.  If it were simply a matter of a bunch of ingredients thrown together and interacting, it would be one thing, but everything is changed by the addition of heat, whether the atmosphere is reducing or oxidizing, the impurities in the materials, etc.

A year or two ago I was trying to figure out the concensus these days on whether glass is a liquid or solid (it's an amorphous solid, though even that is still debated).  I remember reading that even now the chemistry/structure of glass isn't very well understood.

[krsilber]

Stumbled across a possibly contradictory statement about the cadmium sulphide hypothesis.  According to this site (David E.'s?), cadmium sulphide fluoresces yellow and selenium fluoresces orange.  I'm not sure how it fits into the whole picture, but wanted to add it to the thread in the interest thoroughness.
http://www.glassyeye.com/glasstopics/dichroic.html


Also from the Glassyeye site:  "Selenium was originally used as a decolourant to remove the green tinge caused by the natural iron oxides found in glass."  This is very interesting to me.  I've noticed that a lot of Bohemian colorless glass has a dirty orangish cast under UV, and wondered what it was - maybe it's selenium!  I'm probably seeing the same thing Kevin sees in his cut Bohemian glass.