GLASS FACTS by Glass & Art

GLASS FACTS by Glass & Art

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The inventive Mesopotamians

The Mesopotamians were people living in ancient cities like Ur and Babylon, cities that lay between the two big rivers: the Tigris and the Euphrates. They were extremely inventive and came up with, amongst many other things, the wheel and chariot, agriculture, irrigation and agricultural devices like the plow, time, maps, geometry and maths, written language, astronomy and astrology.

Amongst all those innovations was also the invention of glass making, which took place about 5000 years ago. The Mesopotamians did not invent glassblowing, but they did develop techniques like core forming (see left film below), glass fusing (melting glass in a mold), casting (comparable with making bronze items),  grinding and polishing. Core forming, by far the most used technique, is a bit like flameworking or lampworking nowadays: a core made of sand, clay and often animal dung is covered with molten glass, and when cooled down, the core is removed  (today we use stainless steel dipped in a clay-like substance) . With these techniques at hand, they could make fake precious stones (especially lapis lazuli and turquoise were popular), beads, small vessels, small bowls and plates, pendants and the like (see right film below). Glasses for drinking and large objects are not known from that period.

No-one exactly knows how making glass was invented. Myths and theories differ from cooking accidents on the beach (as described by Pliny the Elder, and which is most probably not true) to experiments in ceramics and bronze kilns and experiences at volcanic eruptions.

Mesopotamian core-formed glass bottle, mid to late 15th century BC.
Sold via Christie's for
USD 146,500 (2010), 13.3 cm. high. Photo: Christie's
Egyptian jewelry, 7th - 3rd century BC. National Museum of
Antiquities, Leiden (Netherlands). Photo: Katinka Waelbers

Likewise, not much is known about the production of Mesopotamian glass, but a recipe is written in cuneiform on a clay tablet from the library of King Assurbanipal (668-627 BC), currently to be found in the British Museum (London). The ingredients are immanakku-stone (sand), naga-plant ashes (soda ash, which helps to lower the melting temperature of the sand), 'white plant’ (unknown ingredient) and copper (for the colour).

The Corning Museum of Glass (Corning NY, USA) has studied the translated text of the tablet (see below), and analysed some archaeological samples in 1970. The conclusion of their research is, there was not just one recipe, but a wide variety of glasses, differing according to the desired properties, the origin of the ingredients and the desired colours. They knew how to use metallic oxides to colour the glass, like cobalt oxide and copper oxide (both blue). The maximum size they could melt in one go was about 0,8 litres.

Like in modern days, there were factories that produced glass as raw material (shaped like ingots or chunks) , and there were glass workshops where artists made the actual products. Both the glass and these glass working techniques were exported to other ancient civilisations, such as Egypt, Greece and Rome.


Egyptian glass

Via Syrian workers, the core forming technique was introduced in Egypt  around 1400 BC. The small vessels were, amongst others, used as gifts in burial chambers, hence many examples have survived. Regularly genuine ancient Egyptian vessels that once contained oils, make-up or medicine, turn up for sale in auctions and renowned antiques fairs   Also in Egypt, opaque blue was a popular colour, though they mastered also other colours such as alabaster-like white, yellow, and green.

Egyptians also further developed casting techniques, and introduced lost wax techniques in glass forming, and perfected fusing techniques of small bowls with mosaic-like patterns, also called pressed mosaic bowls.  

Egyptian vessel in the shape of a fish, possibly owned by Queen Nefertiti.
1352 - 1336 BC. 14,5 cm. Currently part of the collection of the British Museum. Photo: Trustees of the British Museum
Bowl of pressed mosaic glass, Alexandria, Egypt, 1st century AD.
Victoria and Albert Museum, London. Photo: Encyclopaedia Britannica

Translation of the clay tablet (by Professor Oppenheim):

“When you set up the foundation of kiln to make glass, you first search in a favorable month for a propitious day, and only then you set up the foundation of the kiln. As soon as you have completely finished in the building of the kiln, and you go and place Kubu-images there, no outsider or stranger should enter the building thereafter; an unclean person must not even pass in front of the images. You regularly perform libation offerings before the Kubu-images. On the day when you plan to place the glass in the kiln, you make a sheep sacrifice before the Kubu-images, you place juniper incense on the censer, you pour out a libation of honey and liquid butter, and then only, you make a fire in the hearth of the kiln and place the glass in the kiln…

If you want to produce zagindurû-colored [greenish type of lapis lazuli] glass, you finely grind, separately, ten minas [about one pound] of immanakku-stone [sand], fifteen minas of naga-plant ashes, and 1 2/3 minas of 'white plant.' You mix these together. You put them into a cold kiln which has four fire openings, and arrange the mixture between the four openings… You keep a good and smokeless fire burning until the glass glows golden yellow. You pour it on a kiln-fired brick and this is called zukû-glass.

You place ten minas of “slow” copper-compound in a clean dabtu-pan. You put it into a hot chamber kiln… You crush and grind finely ten minas of zukû -glass. You open the door of the kiln and throw the ground glass upon the copper compound…When the glass assumes the color of ripe grapes, you keep it boiling for a time…After it has become yellow [hot], you observe some drops forming at the tip of the rake. If the glass is homogeneous, you pour it inside the kiln in a new dabtu-pan, and out of the cooled-off kiln emerges zagindurû-colored glass.”