Whilst I understand Ivo’s comment in reply #51 regarding my discussion comments about gorge de pigeon glass:
I will email you when I get back to my research notes. Until then, I think that ruby the colour is not to be confused with goldruby the process. It is not just dealers and curators who use the term loosely, it is also people who should know better like cmog. And let's not obfuscate the matter with other glass types which may or may not be related. This may be a multiple and complicated misunderstanding. Any testing method for gold content would be a destructive one.
A reply in #36 was presented in a very conclusive way regarding the references by the Hermitage to their ‘gorge de pigeon’ pieces being gold ruby glass:
Reply #36 Oldglassman said:
'Of course you are quite correct but again I would contest the use of the word "evidence", the items linked to above are clearly wrongly attributed by the Hermitage , and could be very old information , personally I would then question the validity of the other entries’and I actually feel it is an interesting discussion on whether or not ‘gorge de pigeon’ glass is wrongly identified as gold ruby glass by the Hermitage, since this is on a thread where it has been stated that gold ruby production ceased in the 1740s and then was not produced again until it’s rediscovery c.1835 by Pohl
(and since I have produced other references in reply #30, #38, #49, to gold ruby glass being produced before 1835)
I understand obviously, that all the authors in those references I have given could be wrong, if, as Ivo says, it is not possible to identify gold ruby glass without destructive testing methods. However, should we also consider that it may be that they (there are a number of references now, not just the Hermitage) have concrete evidences, which have enabled them to state that those pieces are gold ruby glass.
In addition to the two references I gave directly regarding ‘gorge de pigeon’ glass ( on reply#46 point 2) -
La Cristallerie de Clichy Roland Dufrenne, Jean Maës, Christian Capdet, Bernard Maës; and Musee des Arts Decoratif) and the third less specifically but still related reference on that same reply (Walter Spiegl), I have now obtained the book referenced by Bonhams to whom Oldglassman linked as evidence on the reply #36:
‘Baguiers et Verres A Boire du XIXeme siecle’ - Leon Darnis dated 2014
Under a paragraph on ‘gorge de pigeon’ glass it says the following (google translate has been used, please see the original text which I have added at the bottom of this post, for the French description in the book):
Quote –
‘Regarding the gold salts ,, they are used in the form of 'Purple of Cassius' (which we later called 'precipitate of Cassius'), so called in reference to the Dutch XVII century that invented this preparation. This is a mixture of stannous chloride with a solution of gold in aqua regia (nitric acid and hydrochloric acid). Tin was often used in excess and, when cooked, it led to the emergence of a purplish color called 'Pink Hydrangea' or more commonly 'pigeon throat'. This is the usually accepted on this coloration release. But one could believe that there is another possibility. The glassmakers were wont to use manganese as dioxide, called 'soap glassmakers' because it was like bleach vis-a-vis the impurities. However, the excess manganese gave a tint 'Cerulean roughly Dew', that is to say, purplish, with the colorless crystal. In the same way, the manganese in excess or not, could give a purplish hue in the presence of purple of Cassius. Taking advantage of these reflections, it seems that the opaline 'pigeon's breast' that have milky parts probably part of an associated excess tin perhaps to the presence of manganese. However, opaline 'pigeon throat' of a well purplish red color might stand out more from the presence of manganese.’I may be wrong, but it appears to me that they used gold in the form of pourpre de Cassius to make their Gorge de Pigeon glass. From what I have read, that appears to be the way the gold is used in the gold ruby glass?
Again I may be wrong, but it appears to me the difference between the 'appearance to the eye' of the colours of the glass (gold ruby (red) v gold ruby (gorge de pigeon)) is explained by the occasional excessive use of tin (
'Tin was often used in excess and, when cooked, it led to the emergence of a purplish color called 'Pink Hydrangea' or more commonly 'pigeon throat'.') in the production of the gorge de pigeon and the effect that had in the making when combined with the manganese, thereby producing the bright pinky-purply gorge de pigeon.
So it seems to me reading all the references, that both use the gold in the pourpre de Cassius.
I think this is a reasonable explanation as I said before, as to why the Hermitage have their gorge de pigeon coloured glass listed as gold ruby.
It might go some way to explaining why 'gorge de pigeon' ( French glass) and 'Lilac agatin glass' (Bohemian -Buquoy ) and the other 'Purply-pink-opaline-glass-that-looks-like-gorge-de-pigeon' glass (Russian (?) glass in the Hermitage museum that is not gorge-de pigeon incorrectly identified) is so rare.
M. Darnis has 6 pieces of the gorge de pigeon glass in the book dated at 1820-1830.
I have now provided many references (not just 'opinions') to say why I disagreed with this statement:
'‘
Reply #28
Once again from Corning , first phase came with Kunckel c 1684 and ended probably along with the death of his patron in 1688, the second phase began c 1719 and continued in a lesser scale till the 1740s , nothing then till rediscovery c 1835 by Pohl’ – Source given as ‘Glass of the Alchemists’'
If all those references (dating post-2008 when The Glass of Alchemists was dated) are correct then that time frame does not stand anymore.
If however every single one of those references is found to be wrong, then it's probably a good thing we are discussing it.
m
Original script for reference:
‘Concernant le sels d'or,, ils sont utilisés sous la forme du 'pourpre de Cassius' (que l'on appela plus tard 'precipite de Cassius'), ainsi dénommé en référence au hollandais que XVIIeme siecle, inventa cette préparation. Il s'agit d'un mélange de chlorure d'étain avec une solution d'or dans de l'eau regale (acide azotique et acide chlorhydrique). L'étain fut souvent utilisé en exces et, à la cuisson, cela entraina l'apparition d'une couleur violacée appelee 'rose hortensia' ou plus couramment 'gorge de pigeon'. C'est là la version habituellement admise concernant cette coloration. On peut cependant penser qu'il existe une autre possibilité. Le verriers avaient coutume d'utiliser du manganese sous forme de bioxyde, appelé 'savon des verriers' car il agissait comme décolorant vis-a-vis des impurités. Or, l'exces de manganese donnait une teinte 'azurée plus ou moins rosée', c'est-a-dire violacée, avec le cristal incolore. De la meme facon, le manganese, en excés ou non, a pu donner une teinte violacee en presence de pourpre de Cassius. A la faveur de ces réflexions, il semble que les opalines 'gorge de pigeon' que présentent des parties laiteuses participent surement d'un excés d'étain associé peut-etre à la présence de manganese. En revanche, les opalines 'gorge de pigeon' d'une coloration bien rouge violacé pourraient ressortir davantage de la présence de manganese.’