Micro-mineral images of 

crystals from Glass Furnaces

Collected and digitally imaged by Rod Martin

(Baseline of each image is ~2mm unless otherwise stated)

or emerald or em 2 wollast dend zirc
Tabular alumina/corundum crystal Var. Oriental emerald found in wall of green wine bottle Auck 2004 Tabular alumina/corundum crystals Var. Oriental emerald found in wall of amber beer bottle Guangzhou 2007 Tabular alumina/corundum crystals Var. Oriental emerald on wollastonite crystal found in wall of amber beer bottle Guangzhou 2007
Dendritic zirconia
Reaction product of silica on Alumina-Zirconia-Silica refractory at elevated temps
devit
Al. sulphate (+Fe?)
Furnace crown
~1500°C 
Devitrified glass
Devitrified glass
Dendritic zirconia
Reaction product of silica on Alumina-Zirconia-Silica refractory at elevated temps
Lanarkite
Vapour phase (?) growth associated with lead migration in high temp (~1000°C) thermocouple pocket
 Lanarkite
Vapour phase (?) growth associated with lead migration in high temp (~1000°C) thermocouple pocket
Lanarkite
Vapour phase (?) growth associated with lead migration in high temp (~1000°C) thermocouple pocket
Lead alloy showing "needle" growth
Lead alloy showing "pagoda" growth
Mix of crystals from Vapour phase (?) growth associated with lead migration in high temp (~1000°C) thermocouple pocket
Synthetic "ruby" (alumina) from burner ports
~1200°C
Silicon ball formed through reduction of silica in presence of aluminium metal at elevated temps
 "Blue sulphur" 1 "Blue sulphur" 2   Beta-wollastonite crystals  
Umbite/parumbite
Vapour phase (?) growth associated with lead migration in high temp (~1000°C) thermocouple pocket
 Synthetic ultramarine formed in portneck passages (~1300°C)*  Synthetic ultramarine formed in sightbox plug
(~1500°C)*
Beta-wollastonite crystals 100-200mm in length from inside a drained glass furnace

(photo courtesy of Mike)

*"Needless to say, there was a need for a synthetic substitute that would not bankrupt fine artists, or their patrons, or expose them unduly to the predations of 'old women'. At the time that the hunt was on for such a substitute, the first half of the 19th Century, colour chemistry was poorly understood by even its most expert practitioners and serendipity had to play a major part in the discovery of synthetic ultramarine. The first hint to how this substance might be produced was in 1787. Goethe described how glassy masses of a blue material found in limekilns near Palermo were used locally as an ornamental substitute for lapis. 40 years later, Jean Baptiste Guimet, after observing a similar residue at the mouth of glass furnaces, won an open competition in Paris by demonstrating a process where coal, sulphur, soda and china clay, all cheap, commonplace substances, were heated to give synthetic ultramarine.

The sulphur is trapped in the crystal lattice in a special form. Elemental sulphur, the stuff that goes into fireworks, is a primrose yellow crystalline solid. The sulphur in ultramarine is an altogether more exotic beast. In elemental sulphur, which is stable, eight sulphur atoms are joined together in a ring. In ultramarine, three sulphur atoms are joined in a chain and carry a surplus, fidgety and highly reactive electron. It is this itinerant electron that intensely absorbs yellow light, and makes ultramarine very susceptible to the influence of acids, which decolourise it rapidly. This fragile, reactive blue molecule is trapped inside a transparent octahedral cage of aluminium, silicon and oxygen atoms. Nothing can get at it and, being bulky, it cannot get out of its cage: the chemical equivalent of an insect in amber, trapped when the molten sodalite crystallised around it and preserved almost indefinitely from environmental depredation.

Today, ultramarine is still produced and used as a pigment. If selenium or tellurium is substituted for sulphur in its manufacture, intense red and purple pigments are produced. Ultramarine was used in laundry whitener (the 'Blue Bag' of old).
" http://www.bbc.co.uk/dna/h2g2/A656804

3D coin

Song Dynasty coin in 3D
 
 
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