Author Topic: Webb's Alexandrite  (Read 3749 times)

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Offline Jim Sapp

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Re: Webb's Alexandrite
« Reply #30 on: February 20, 2007, 01:21:07 PM »
Thanks for the clarification.

Not to change the subject too much.....has anyone seen any examples of "pressed" Alexandrite by Webb.  I am assuming all the Webb examples are either free blown or mold blown. 



Offline Jim Sapp

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Re: Webb's Alexandrite
« Reply #31 on: April 14, 2007, 10:38:37 PM »
Jim
Did you do the blacklight test?  I would be interested to hear the results.
Dave
aka: Mr. Vaseline Glass

Hi,

It has been some time since we discussed this piece of Alexandrite.  However, I have found someone with both a long and short wave blacklight.  The Alexandrite does indeed fluoresce a green/yellow under long wave blacklight.  It also fluoresces under short wave but not as brightly.  The geologist that help me suspected uranium oxide produced the green/yellow florescence.  He suspected either cobalt or iron oxide produced the blue color.  But, his specialty is "rocks" not glass.

An added note, seeing my Burmese under a professional blacklite was a real treat.  Glows like you wouldn't believe.

Jim.



Jim.


Offline mrvaselineglass

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Re: Webb's Alexandrite
« Reply #32 on: April 15, 2007, 01:25:29 PM »
Jim
I suspected it would glow.  If nothing else, that confirms that you do indeed have a piece of alexandrite, and not something else.  Webb used uranium dioxide in their 'alexandrite' color, as opposed to Stevens & Williams, who did not. 

Thanks for the info!

Regards
Mr. Vaseline Glass


Offline Moultermike

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Re: Webb's Alexandrite
« Reply #33 on: November 01, 2010, 02:08:49 PM »
I don't have a piece of Webb's Alexandrite, but I purchased a couple of vases recently which shade to violet at the top in the same way that Webb's Alexandrite does. I always examine "Alexandrite" glass with a spectroscope, which easily picks out the neodymium which is used in normal dichroic Alexandrite. My new bits don't contain neodymium, so the colour comes from some other source.

The general form of the colouring in Webb's Alexandrite is consistent with the glass containing a colloidal metal which becomes visible when the glass is re-heated at the glory hole. (This is done with colloidal gold in Amberina glass). I haven't been able to discover what that metal is, but I will keep searching for information.

I have tried a Geiger counter on a piece of probable Webb's Alexandrite. It was radioactive, which is consistent with uranium glass.

I notice that Locke's July 24th 1883 patent for Amberina glass apparently mentions other colours. I don't have a copy of that patent but it is probably worth getting one.


Offline Jim Sapp

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Re: Webb's Alexandrite
« Reply #34 on: November 01, 2010, 03:17:53 PM »
I notice that Locke's July 24th 1883 patent for Amberina glass apparently mentions other colours. I don't have a copy of that patent but it is probably worth getting one.

Thanks for information.  I have put a copy of Locke's 1883 patent for Amberina on-line for your reference.  It does indeed refer to other colors.  The Patent is at:

Jim.
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Offline Moultermike

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Re: Webb's Alexandrite
« Reply #35 on: November 02, 2010, 08:36:45 AM »
Thanks, Jim. I note speculation about the metal used to make the blue/violetcolour. It isn't cobalt blue or manganese amethyst. I have never come across iron making a blue colour; it usually gives green (+2 oxidation state) or brown (+3 oxidation state). I have come across references to tellurium being used for blue glass. The chemically related selenium is used for red, which it probably produces in the colloidal state. The best way to discover the metal responsible would be for someone with a piece of Webb's Alexandrite to chat up a friendly contact with access to the analytical technique of X-ray fluorescence. That can pick up all the chemical elements present in a sample, except for the lighter ones, which can be ignored in this case. It is a non-destructive technique.

Moultermike


Offline Bernard C

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Re: Webb's Alexandrite
« Reply #36 on: November 02, 2010, 09:17:08 AM »
...   It is a non-destructive technique.   ...

Over here word already went round a year or two ago to look for and keep any broken example of Alexandrite (or any other heat sensitive glass) for analysis.   It's worth reminding everyone.

That was good of you, Jim, to put this interesting Patent online.

Some caution should be used when reading Locke's patent as patents and design registrations are often more widely embracing than the patentee's actual state of development.   Some over here go even further and are deliberately misleading — for processes that are known not to work, for example — as patents and design registrations are very public documents and are often reproduced in full in the trade press.   Anything to gain an advantage over your competitors, both in the home and international marketplace.

Bernard C.  8)
Text and Images Copyright 200414 Bernard Cavalot


Offline Moultermike

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Re: Webb's Alexandrite
« Reply #37 on: January 21, 2011, 03:05:16 PM »
This morning I and a student at the university of Kent at Canterbury did some spectroscopy on a Webb's Alexandrite wine glass. I had established previously that the body of the glass was radioactive, so the yellow is caused by uranium. W.W. Weyl in his book "Coloured Glasses" (ISBN 0-900682-06-X), gives three possible ingredients for purple glass; manganese, nickel and titanium. The maximum spectral absorption of the purple in the wine glass was near 575nm, which is consistent with titanium, but not with manganese or nickel. He stresses the difficulty of reducing titanium to the purple (+3) form. However, I suspect that re-heating in a chemically reducing atmosphere, or even covering the edge of the glass with oil and re- heating it, would form purple Ti3+.

I suspect, therefore, that Webb's Alexandrite is based on uranium and titanium, though X-ray fluorescence would be needed to confirm this.


 

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