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Author Topic: Yellow tints in clear glass  (Read 3244 times)

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Offline chloe

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Yellow tints in clear glass
« on: November 05, 2008, 02:29:34 PM »
Hi

I've had a read through some old posts on here about this topic and am now more confused than ever!

Why does some clear glass have a yellow tinge?  Is it a sign of a particular age/location?  Completely irrelevant?

Have included photos of two celery jars which seemed to be clear until I photographed when a yellow tint appeared.

Thanks


Offline Lustrousstone

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Re: Yellow tints in clear glass
« Reply #1 on: November 05, 2008, 03:46:58 PM »
It's just the recipe that was used for the glass. Time has moved on, recipes for clear glass have changed, the consumer expects their colourless glass to be completely colourless, Grey/purple, now that's a slightly different matter


Offline Ivo

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Re: Yellow tints in clear glass
« Reply #2 on: November 05, 2008, 04:42:55 PM »
Interesting point. I'm not sure if this has universal validity but a yellowish tinge to me indicates glass that was made in the 1920s. On a market stall of assorted table glass I can detect the items from that period by looking at the colour. Now most table glass encountered here is Leerdam or was made in Germany; and it seems in England and in Bohemia there is much more semi-crystal which has a neutral to bluish tinge. And anything recent has a distinct greenish windowpane colour while old glass is decidedly greyish.
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Offline Pinkspoons

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Re: Yellow tints in clear glass
« Reply #3 on: November 05, 2008, 04:59:59 PM »
Holmegaard tableware was fairly bright and clear from the 1900s until around the early 1940s (possibly slightly earlier), when it took on a decidedly yellowed hue. This was true until at least the mid/late 1950s. After this it went back to being very clear for a period, and in the mid 1970s it acquired a blue-tint in a lot -but not all - of their designs.

So for Holmegaard glass, it's a very useful dating tool, especially if it's a series that has been in production for several decades.


Offline deco.queen

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Re: Yellow tints in clear glass
« Reply #4 on: November 05, 2008, 05:04:26 PM »
Are you sure it isn't just from the lighting used?  When I take a picture I often have that tinge but it's just the light bulb. Just my 2ยข.
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Offline Lustrousstone

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Re: Yellow tints in clear glass
« Reply #5 on: November 05, 2008, 05:07:42 PM »
No the Chance celery at the bottom is definitely yellowish glass - I have one, but that's 50s/60s


Offline chloe

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Re: Yellow tints in clear glass
« Reply #6 on: November 05, 2008, 05:25:19 PM »
THanks for your input.  The pictures are taken with only a daylight lightbulb, so it's unlikely to be the lighting.  I think, if anything, looking at them mornally (with standard lightulbs) makes me more likely to discount any yellow tinge as lighting - and perhaps the contrast between the glass and the very 'white' light of natural daylight just emphasises what was there all along.

So basically (in far too much of a quick summary) - if you know roughly where the glass is from, geographically, then the tint can help with dating?


Offline krsilber

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Re: Yellow tints in clear glass
« Reply #7 on: November 05, 2008, 05:51:52 PM »
I've heard - and I don't know if this is true - that glasses with selenium used as a decolorant can turn slightly yellowish over time, and that this might have something to do with exposure to sun.  It would be interesting to compare yellowish vs. greyish glass from the same company to see how each fluoresces under UV.

As far as using glass tinge for dating, my feeling is that there is some limited use, but one has to be very careful and it might not go by geographic origins alone; it may be company-specific, too. 
Kristi


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Offline Adam

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Re: Yellow tints in clear glass
« Reply #8 on: November 05, 2008, 07:26:23 PM »
A lot of Sowerbys' "colourless" glass develops a distinct yellowish tint when exposed to sunlight, especially that made in the 1940s and 1950s.  Arsenic was used in the mixture both as an aid to decolourising with selenium and cobalt and as an aid to speed up melting and hence to increase production.  The latter effect needed many times more arsenic than the former.  It was only after some years that we noticed the horrible colour effect which was put down to using far too much arsenic.  To this day I cringe and feel guilty when I see this, mainly at boot sales.  For the record, just in case anyone has access to a suitable kiln, if the article is re-annealed, the effect disappears.  A sideline for someone, Adam A?

No doubt other manufacturers fell into the same trap.

Adam D.


Offline Lustrousstone

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Re: Yellow tints in clear glass
« Reply #9 on: November 05, 2008, 07:34:35 PM »
No, I don't think you can use a yellow tinge for definitive dating in general. I have a commemorative paperweight that was certainly engraved in 1995 from a blank that was probably made at the St Helen's Ravenhead glassworks (it was produced for the regeneration project in the Ravenhead area) that is definitely yellowish. You can probably say of decorative and tableware that if it's yellowish, it may older rather than newer. Then you have to apply other dating criteria such as style and wear.

 

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