Author Topic: What happened to yellow and red?  (Read 634 times)

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Offline Wuff

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What happened to yellow and red?
« on: November 19, 2011, 02:45:33 PM »
I was given this weight recently - nothing spectacular at first sight: I would say a Chinese weight using Murano canes.
Height 77 mm / diam. 54 mm / weight 302 g.
The (not quite circular) base is not polished, but much clearer than the usual Chinese weights - so one can nicely view the canes - blue - white - yellow - red. Viewed from above, however, only blue and white are there, yellow and red (apart from the sides) have turned dark grey.
What happened? Contamination of the set-up plate, a temperature problem .... or what?
Any suggestions would be welcome, and also, of course, any comments on my identification.
Best regards - Wolf
Wolf Seelentag, St.Gallen
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Offline tropdevin

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Re: What happened to yellow and red?
« Reply #1 on: November 19, 2011, 03:25:54 PM »
***

Hi Wuff.

If you get coloured glass too hot you can 'burn out' the colours. I suspect this was overheated in the glory hole after pick-up, so the top surface was damaged. Another (slight) possibility is that the colours are sensitive to reducing / oxidising atmospheres, and the colours have been oxidised.

On the ID front, I have never been convinced that there were many paperweights 'made in China with Murano canes'. There may have been some, but I suspect Murano canes were quickly copied. The canes in your weight do have a Murano air to them though. Could it be a Murano whose base was never polished because of the damage to the canes?

Alan
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Offline chopin-liszt

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Re: What happened to yellow and red?
« Reply #2 on: November 19, 2011, 03:29:45 PM »
 :spls:
hi Wolf,
The normal "dome" shape of the canes inside seems to have been dented - I assume when the final gather of glass was added to the organised cane base part during construction -

would this perhaps be corroboration for a notion that the final gather was too hot and perhaps "burned" the colours, heat-striking them to create the different colours on the top?

It does suggest lack of knowledge about constructing a weight.

(cross posting  :-[ - I agree with Tropdevin - it could well have been "burnt" in the glory-hole!)
Cheers, Sue (M)

“All things are subject to interpretation. Whichever interpretation prevails at a given time is a function of power and not truth.” Friedrich Nietzsche


Offline Wuff

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Re: What happened to yellow and red?
« Reply #3 on: November 19, 2011, 06:37:00 PM »
Hi Wuff.
If you get coloured glass too hot you can 'burn out' the colours. I suspect this was overheated in the glory hole after pick-up, so the top surface was damaged. Another (slight) possibility is that the colours are sensitive to reducing / oxidising atmospheres, and the colours have been oxidised.
Thank you for confirming one of my suggestions as likely cause: overheating - which obviously would be more critical for some colours than others.
Now - at which state?
1.step: canes are laid out on heated plate. What doesn't really show up in the images: the fact that canes are all of slightly different length shows up when viewing the weight through the base. So the cane ends sitting on the plate turned grey - unlikely at this stage, as the plate wouldn't be that hot.
2.step: canes are taken up with a first gather of glass - which doesn't have any effect on the colours at this end, and even less likely at the other cane ends.
3.step: what? I always assumed that a second gather of glass would be added to the other end - or would the canes and first gather go directly into the glory hole? If my assumption (second gather) is correct, I would be surprised that this would still be too hot, after being transferred from the glory hole to the (unfinished) weight. On the other hand - if a second gather is added outside, and then the entire piece is put into the glory hole again, I would assume to see the overheating effect not on one side only.

On the ID front, I have never been convinced that there were many paperweights 'made in China with Murano canes'. There may have been some, but I suspect Murano canes were quickly copied. The canes in your weight do have a Murano air to them though. Could it be a Murano whose base was never polished because of the damage to the canes?
I am sure Murano canes have been copied in China - but these would be exceptionally good copies: they all show up in the Effetre catalogue (not sure which year my copy is), and two I actually have amongst my sample canes.
If not made in China, I see two possibilities:
1. Made in Murano and not finished - but is polishing that time consuming that a "second" would be ground flat, but not polished?
2. Made somewhere else in the world - as we know Murano canes were also used e.g. in the USA, but I have never heard about US makers copying Murano canes. Would this be more likely?

Thank you, Alan and Sue, for your comments - Wolf
Wolf Seelentag, St.Gallen
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Offline tropdevin

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Re: What happened to yellow and red?
« Reply #4 on: November 19, 2011, 07:08:14 PM »
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Hi Wuff

My understanding - based on watching paperweights being made, and also the week I spent making paperweights with Willie Manson - is that it is standard practice to pick up the canes with a gather of glass, then re-heat in the glory hole, and compact the canes (you need to get the cushion shaped, and to squeeze out the air from between the canes) - this usually means re-heating the canes and working them several times. That gives plenty of opportunity for over-heating the exposed canes. Only when the canes are properly compacted and the cushion shaped would the encasing gather be added, which would protect the canes somewhat.

Alan
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Offline chopin-liszt

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Re: What happened to yellow and red?
« Reply #5 on: November 20, 2011, 10:26:26 AM »
Exactly, Alan.
I watched Mike Hunter making a compact cane weight at the Edinburgh Conference - the cushion of canes needs shaped and compacted and heated to a level it won't crack when the final gather is added to form the full weight.

Are there videos/pics of this from the Conference here somewhere?
Cheers, Sue (M)

“All things are subject to interpretation. Whichever interpretation prevails at a given time is a function of power and not truth.” Friedrich Nietzsche


Offline Frank

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Re: What happened to yellow and red?
« Reply #6 on: November 20, 2011, 10:33:52 PM »
On Scotlands glass... I think Sue
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Offline Sach

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Re: What happened to yellow and red?
« Reply #7 on: November 20, 2011, 11:36:51 PM »
but is polishing that time consuming that a "second" would be ground flat, but not polished?

Absolutely.  It takes considerable time and several steps to polish the base on any paperweight.

As for the color change, I've never heard any glassblower speak of burning out a color.  Repeated high heat will "burn out" fluxes from the glass and can alter the coefficient of expansion enough to render it incompatible, but that's not what we see here.  Lampworkers speak of "burning the glass" if they overheat it and boil out the fluxes.  This does result in black ugly glass but it's next to impossible to overheat a mass of glass in the gloryhole the way you can do a small bit in a torch where the flame is fed with oxygen.

Many colors are sensitive to heat in that they take time to develop after the glass is taken to a high temperature.  But failure to provide that time just results in a pale color, not a blackened one.  I do not know what happened in this weight.  I do know that both reds and yellows tend to be easily contaminated by either lead or silver and the result of such contamination is a dark discoloration.  My guess would be that this glass was worked with a contaminated block or paper which had picked up a bit of one of those metals while working a previous piece.  The only other explanation I can see would be that the glass was hit with a venturi type torch in a manner that left a lot of fuel on the glass.  You can do that if you hold the torch too close.


Offline Wuff

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Re: What happened to yellow and red?
« Reply #8 on: November 21, 2011, 08:18:38 PM »
Absolutely.  It takes considerable time and several steps to polish the base on any paperweight.

Thank you for your comments, Sach - so it makes sense to grind the weight flat, after the mishap was discovered, but not polish it - to be sold as a second. Consequently this could actually be a Murano weight, not just a weight with Murano canes?

Thank you all for your comments: I find it very interesting that a piece without any real value can still stipulate fascinating discussions :).
Wolf Seelentag, St.Gallen
Interested in any aspect of Scottish glass? Have a look at Scotland's Glass.


 

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