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Monday, 7 November 2011

Did Anglo-Saxons use crystal lenses?

Visby lens, 11th century
Anglo-Saxon jewelry such as seen in the Staffordshire Hoard and Sutton-Hoo burial is of astonishing intricacy. It has always been a mystery how such fine work - both gold filigree and garnet cloisonné - could have been achieved without modern aids.
For example;  each corrugated reflective gold foil underlying each tiny cut garnet is between 0.01 - 0.25 mm thick and the waffle-like corrugations on their surface are often 5½ to the millimeter. The garnets themselves are often very thin, between 0.5 - 0.75 mm and only about 2mm x 2mm across.
How could the Anglo-Saxons have been capable of crafting such minute detail, hundreds of years before the first glass lenses were invented?



Staffordshire Hoard hilt collar; tiny waffle-pattern gold backing is visible through the minute garnets


Today we would use a magnifying lens of some sort for such fine work but it has always been assumed that no such device was available in the 7th Century CE. It has been speculated that children or folk with myopia might have been utilised to do such fine work but the idea that the early medieval craftsman might have used a lens was not considered because it was accepted wisdom that such lenses dated only back as far as the latter Middle Ages when the glass workshops in Northern Italy started to produce optical glass and pioneers such as Francis Bacon began work on the science of optics.

Accepted wisdom was rocked when, in September 1999, Schmidt, Wilms and Lingelbach published a paper entitled "The Visby Lenses" detailing the optical qualities of a hoard of Viking-Age rock crystal objects found on the island of Gotland.
*Greek lens, as seen recently at Rhodes

In fact, biconvex rock crystal lenses are much more ancient even than this. Such were certainly made by and used by the Ancient Greeks. Large numbers are on show in museums* but have only recently been labelled as other than jewelry.
Such are mentioned by the Greek playwright Aristophanes in 420 BC, in ‘THE CLOUDS’.
STREPSIADES: “Have you ever seen a beautiful, transparent stone at the pharmacist's, with which you may kindle fire?”
SOCRATES: “You mean a crystal lens.”
STREPSIADES: “That's right. Well, now if I placed myself with this stone in the sun and a long way off from the clerk, while he was writing out the conviction, I could make all the wax, upon which the words were written, melt.”
A hoard of rock crystal lenses, some set in silver mountings, were discovered at Viking sites at Visby on the island of Gotland. The silver-work dates to the 11th Century CE but the lenses may be older. They would have been ground and polished on a turning lathe, either locally or somewhere in the Middle East. Quite possibly, they were imported via Byzantium. At this time, Gotland was a critical trading hub, linking Europe with the East.

Necklace of viking crystal lenses

The image quality produced by these crystal lenses is almost as good as modern aspherical lenses. The best measures 5cm in diameter.
Spherical crystal pendants are not uncommonly found in early Anglo-Saxon graves. One such case, from a woman's grave at Wigber Low near Kniverton in Derbyshire (approx. 30 miles from the site of the Hoard) is dated to the 7th Century, and provides clear evidence that polished rock crystal was available in Mercia during the time of manufacture of many of the Hoard's most intricate items. It is therefore not impossible that lens-crystals were also available and able to be used by certain favored craftsmen.

The Old English name for rock crystal was cristalla. More telling is another Old English word : ðurhscynestan - literally ‘through shine stone’.

Did the Anglo-Saxons use such lenses? - it is impossible to prove but is at least worth considering.

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