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Author Topic: ID help with classical style vase please  (Read 9516 times)

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Offline Paul S.

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Re: ID help with classical style vase please
« Reply #80 on: January 24, 2013, 10:33:26 PM »
o.k................... so we shoot the translator!                   As I believe we've mentioned earlier, it would seem that the original French word was 'opalin' - as stated by Newman and possibly others - to have been used by Baccarat c. 1823.

If there is a sunset glow, then I'd be tempted to always go with 'opalescent' - no matter what colour - provided there is some translucency (and a lot in those pieces such as Salviati for example).
Alabaster will not fit this description, but is fairly distinctive, so shouldn't be a problem.............other material also lacking a natural glow and opaque in nature is probably best described as opaque glass, whatever the colour.
Certain C19 materials that react to u.v. should be given their correct trade name.

Will someone please confirm if the French 'pigeons neck' and 'soap bubble' colours are the result of a sunset glow?

But Christine, you didn't answer the question..............is opalescent the result of re-heating, or not please??

Feel free to condemn or otherwise the above.  :)




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Offline flying free

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Re: ID help with classical style vase please
« Reply #81 on: January 25, 2013, 12:09:44 AM »
 Paul, I do apologise.

What I was trying to identify was whether Mel's vase was opaline glass.  And in my researching info on opaline glass I found a number of discrepancies as we have discussed, so I wondered
a) what the actual description of opaline glass is
and
b) has the description name changed over the years or
 has the product changed immensely from when it was first made.

Christine, I don't know - I was just showing references that a museum show of opaline glass from 1840 and it's not opalescent - I thought they might be a solid reference for the term.


I have a question though -

In the exhibition catalogue of 1851(reproduced in CH British Glass) a vase that doesn't look what I would call opalescent although admittedly hard to tell, is described as opalescent (the apparently MW & Co one as discussed earlier but subsequently thought to be Richardsons), and
Roger Dodsworth has referred to that vase as probably being Richardsons on the basis it was '..opalescent glass'.  Did Richardsons make opalescent(as we know it) glass in the 1850's?  I can't find any other Richardsons glass in the books i have ( not many) that are opalescent.  Do you know of any please?

and of course that brings us back to the Art-union magazine of 1847 where it discusses the vases in what I believe are the same range as Mel's and titles the document 'Opalescent glass'.

I do wonder whether the Count's translator used the word 'opaline' as in the French word that the Count had used, but that the English translation at that time was actually opal'escent' as in the English version of opal' ine' i.e opal'like' but it did not necessarily have to have fiery opalescence as we know it to be described as opal'escent'.  It merely meant opal -like and could be describing fiery opaline as in bulle de savon or not as in other 'flat' opaline glass, and was an English translation of opal 'ine' i.e in French that might have also meant opal-like.

And over time that word got appropriated for use on pieces that had been reheated and showed a fiery opalescence (as we know the term), and then the French word 'opaline' became general use for a semi transparent glass that has been made using an opacifier. 

m






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Offline Lustrousstone

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Re: ID help with classical style vase please
« Reply #82 on: January 25, 2013, 07:14:58 AM »
Quote
is opalescent the result of re-heating, or not please??
Yes but I don't know whether it is true in all cases, but I suspect so.

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Offline flying free

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Re: ID help with classical style vase please
« Reply #83 on: January 25, 2013, 10:35:52 AM »
I have quoted below from a Treatise from 1832. (link to Treatise given at the bottom)
It seems to me that what is being described is glass replicating the opal stone, but not using reheating and not producing what we call today as opalescent glass.  It seems to me the mix of glass in the batch once cooled and hardened as a vase, gives off the play on colours as a result of the constituents of the batch and is not reheated to produce an opalescent (as we know the word) effect.  I'm open to correction here.
Also, the description is given under the heading 'Opaque white glass'.  I think opaque is being used as a word to describe any glass that is not transparent.  i.e. it is not opaque v translucent v transparent, but merely describes the difference between glass which is transparent and glass which is not.  There is no in between (i.e. translucent or semi-opaque) just it is transparent, or it's not.  If it's not then call they call it opaque.

This is a 'treatise'  from 1832
Source:  The treatise on the progressive improvement and present state of the manufacture of porcelain and glass - 1832 (I think it was written by George Richardson Porter , produced for Longman, Rees, Orme, Brown & Green )

Page 281 
It comes under the header Chap XIII White Opaque Glass.  Prior to writing the description I give below, the author gives two formulas for producing white opaque glass from two makers and then goes on to say:

'Fontanieu has given directions for imitating the peculiar lustre of the semi-transparent opal, by mixing 576parts of hi sglass no 8 (Chap VII) with 10 parts of muriate silver, 2 parts of magnetic iron ore, and 26 parts bone ash.  The beautiful play of colours exhibited by the "precious opal" is deservedly an object of much admiration, and it has always been a subject of interest to imitate successfully so pleasing an effect.
Ornamental pieces of opal glass have usually been obtained from France, but in their production, of a quality fully equal to these importations, may now be witnessed in the London Glass-works.
The peculiar delicacy and beauty of this glass does not appear while it remains in a state of fusion or at a red heat; and are not fully developed until it is sufficiently cooled to acquire its quality of brittleness.

Other coloured glasses which are opaque, are made by the same processes as are followed by the transparent glasses of the like colours, substituting for the common vitreous base, one of the above described, opaque-white glasses.'

http://books.google.co.uk/books?id=yr8UAAAAQAAJ&pg=PA282&dq=richardson+opal+glass&hl=en&sa=X&ei=XEwCUYO9NKuk0AXq_oGwDw&ved=0CC4Q6AEwAA#v=onepage&q=opalescent&f=false

m

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Offline Lustrousstone

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Re: ID help with classical style vase please
« Reply #84 on: January 25, 2013, 12:11:29 PM »
This may help with the opalescence issue, but not with opaline
http://www.patternglass.com/KindOpal/kindOpalHearn.htm
and this
http://www.glass.co.nz/opalesc.htm

The early chappies will be describing the cooling effect version

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Offline Paul S.

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Re: ID help with classical style vase please
« Reply #85 on: January 25, 2013, 11:28:12 PM »
No problem m :)

quote..............."Yes but I don't know whether it is true in all cases, but I suspect so"   -   this, as we can now see from Angela Bowey's article, appears not always to be true.
However, the following from m does appear to be correct..................quote..............."It seems to me the mix of glass in the batch once cooled and hardened as a vase, gives off the play on colours as a result of the constituents of the batch and is not reheated to produce an opalescent (as we know the word) effect."  -  but it seems to be true only when speaking of pressed glass.
Those thicker parts of the piece which cool at a slower rate are the areas that produce the sunsect effect  -  as in Lalique, Sabino, Jobling, and other similarly produced material - and importantly only where the item is made by pressing.

In material such as Davidson's Pearline in Primrose, Blue and Moonshine, where re-striking is necessary to produce the dense opaque creamy rims, the opalescence is seen only in or very close to those opaque extremities  -  and we are told is produced only by re-heating (so doesn't  occur due to cooling process as in the Lalique etc.)

In respect of the many articles on 'opaline' there doesn't seem to be any mention of reheating - or did I miss that?

Is the Salviati re-heated to acquire opalescence, or does that occur simply due to cooling?

I get the impression that 'opalescence has been arrived at via several different processes, although arsenic and phosphates seem to be common denominators.

Trying to cut to the chase on all of this, I think that the nub of the matter is that m was trying to discover if in fact there were two kinds of 'opaline'  -  one that had a sunset glow, and another that didn't.
In my opinion I suspect not, and that all opaline has a sunset glow, to some degree.                  Just as a matter of interest, I'll post a pic tomorrow some time of a milky-coloured strongly opalescent stemmed and footed sweetmeat/desert dish, with a folded foot, which might be late C18.

thanks to Lustrousstone for the links.





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Offline flying free

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Re: ID help with classical style vase please
« Reply #86 on: January 25, 2013, 11:39:16 PM »
thank you :)

Paul, I'm not sure on your conclusion here
'However, the following from m does appear to be correct..................quote..............."It seems to me the mix of glass in the batch once cooled and hardened as a vase, gives off the play on colours as a result of the constituents of the batch and is not reheated to produce an opalescent (as we know the word) effect."  -  but it seems to be true only when speaking of pressed glass.'

...I think the two vases I showed from Christy's auction give off an opalescent effect  as a result of cooling and of being glass made possibly in the way described in the recipe I linked to.
  Also the recipe link quote I gave from the Treatise written in 1832 I think is a recipe for producing that effect via cooling rather than reheating and I suspect that was to do with blown glass not pressed glass.  I think  :-\ 
m

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Offline Lustrousstone

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Re: ID help with classical style vase please
« Reply #87 on: January 26, 2013, 12:30:34 PM »
It wouldn't matter how the glass was made for cooling opalescence to be achieved; it would depend on the formula

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Offline flying free

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Re: ID help with classical style vase please
« Reply #88 on: January 26, 2013, 02:01:08 PM »
So would I be right in saying-
1)  glass mixed in the batch with a particular type of  opacifier will cool to become semi translucent  (at varying degrees of translucency)
2)  If it does not have the opacifier it will be transparent?

I state the phrase 'a particular type of opacifier' because I wonder if tin oxide used in milchglas and lattimo is what makes it cool to opaque rather than semi-translucent and whether bone ash is the ingredient that gives semi translucent glass it's translucency?
 

If there is semi translucent glass that is both flat (i.e. no opalescent effect) and another semi translucent glass that displays opalescent effect on appearance, what  was mixed in the batch to produce an opalescent effect upon cooling? It must have been something added as otherwise it would have appeared as 'flat' semi translucent glass when it cooled.


I'm still trying to get my head around what appears to me to be transparent glass (say the example of Davidson pearline)with opalescent edges and how that is done.
Is it that something that is in the batch that only when reheated  gives the opalescent effect,i.e  on the edges?
I'm thinking it must be different to the recipe used to make opalescent semi-translucent glass which appears opalescent when cooled, because otherwise the whole thing would just appear opalescent when cooled.   If you see what I mean?

I'm just pondering Paul's Salviati question here where my whole jug just has a faint opaline appearance (very translucent) and opalescent appearance, but in parts is very opaline and opalescent so wondering if in that case the extra ingredient added to make it cool to semi translucent and opalescent also meant that in parts it could be reheated and appear even more opaline and opalescent.

But on Davidson pearline, some of the pieces I've had appear transparent but only opaline and opalescent on the edges by comparison.

I don't know if I've asked those questions very well  :-\
m


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Offline Lustrousstone

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Re: ID help with classical style vase please
« Reply #89 on: January 26, 2013, 03:27:22 PM »
A straight opacifier such as tin oxide does what is says on the tin, makes it opaque, but how opaque will depend on the concentration. Think semi-skimmed milk, i.e., translucent and double cream, opaque. The less opacifier, the more translucent. It's effectively a stable suspension, as a glass melt containing an opacifier will be. That property has nothing to do cooling and will show no light effects because what you have is a powder suspended in a supercooled liquid. There is no chemistry involved.

The cooling type opalescence results from a particular compound (bone ash or/and arsenic I think) crystallising out in the glass when it is cooled very slowly, slower than normal. The tiny crystals reflect the light to reduce the transparency and produce the cloudiness, i.e., translucency, and the opalescent (light reflection, refraction and transmission effects). The thicker the glass, the less transparent it is. This is a physicochemical thing.

The pearline effect is more related to the latter; it is either a reaction that produces a white opaque compound on reheating or, more likely, the reheating causes "something" to crystallise out. The more heat applied the greater the concentration of crystals and the more opaque the glass. The crystals would also explain the opalescence seen at the edge of pearline.

I might not be quite accurate, but that's how it all makes sense to me as a chemist.

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