Micromineral images

Micro-mineral images of

crystals from Glass Furnaces

Collected and digitally imaged by Rod Martin

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


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

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

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

Song Dynasty coin in 3D

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