Ancient Egypt was mass-producing its own glass objects more than 3,000 years ago, according to evidence from digs in the country's eastern Nile delta.
Red glass has turned green due to corrosion of the copper it contains (Image: Birgit Schoer)
The finding rejects a theory that the Egyptians simply got their glass from the Mesopotamians and reworked it.
A UK team identified the first known site from Egypt with direct evidence of "primary" glass production, meaning the Egyptians made the glass from scratch.
The University College London experts describe their discoveries in Science.
The earliest evidence of glass production comes from Mesopotamia in 1550 BC. It is generally accepted that the industry spread from here to Egypt, where it appeared by 1500 BC.
The new findings come from studies carried out by Edgar Pusch and Thilo Rehren, from UCL, of archaeological debris from a 13th Century BC glass factory at the site of Qantir-Piramesses.
"We have a small amount of textual evidence and other indications that Egypt was importing its glass from Mesopotamia but nothing else," co-author Thilo Rehren told the BBC News website.
"We had evidence of Egyptians making glass objects, but apparently with glass they got from abroad. We can now definitively demonstrate that Egypt did make her own glass in addition to importing it."
The artefacts at this large-scale factory indicate that the raw materials were first partially heated inside vessels that may have been recycled beer jars, then crushed and washed.
In the second part of the process, the glass was coloured and heated inside specialised crucibles, forming round ingots that were exported to other workshops.
Glass was colored and heated in ceramic vessels
Here, the glass was re-heated and made into decorative objects.
The containers would have been smashed to remove the glass inside. These glass objects, usually containers for perfumes or other liquids, were a highly prized commodity.
Of the 40 glass vessels from Qantir, 37 are red in colour. Red glass is relatively rare amongst known finds of glass objects from this period; most from Egypt are blue, while Mesopotamia specialised in white and yellow glass which required antimony from the Caucasus to produce.
A highly skilled process was necessary to produce red glass and the factory at Qantir probably specialised in making this colour. It required the metal copper to produce the red colour and needed the workers to regulate reduction and oxidation (redox) conditions in the process.
"My suggestion is that these two 'superpowers' (Egypt and Mesopotamia) were, on a friendly basis, exchanging as gifts glass ingots of different colours: 'You give me two reds, I'll give you two whites'," said Dr Rehren.
"My preferred metaphor in modern terms is nuclear power. If you need power, you can get electricity in various ways. But it is prestigious to have nuclear power - to show off with it and be part of the club of the few. You also need to know the right people to get it."
Dr Caroline Jackson, an archaeologist at the University of Sheffield, said the findings "put forward more evidence for Egypt being producers of elite materials".
But she added there was little evidence that red glass found its way outside Egypt through exchange.