Sir Lawrence Alma-Tadema's Victorian-era portrait of a Roman "Picture Gallery" imagines what life was like for wealthy Roman collectors at the time of Augustus. Note the magnifying glass in the leaning woman's hand. The painting was completed a decade after the discovery of the "Loupe of Sargon," a rock crystal lentoid from the 8th century BC.  

Henry Jesionka discovered a cache of artifacts from an ancient Roman film projector on a beach in Nin, Croatia, in 2011. Absent from this find was any evidence of optical lenses.

There is much debate about the existence of ancient optical lenses. Some scholars claim that rock crystal or topaz was used to observe the stars as early as 2283 BC, in China. The eminent archaeologist Sir Arthur Evans discovered rock crystal lenses, plano-convex in shape, in the Middle Minoan IIIB Temple Repositories at Knossos, in 1921, along with a "royal Draught Board" with ivory and crystal inlays backed with silver foil. The lenses were dated to 1600 BC. Three years later, he unearthed three “bossed crystal discs,” from 1400 BC, in a nearby cemetery at Knossos.

“There are now 23 ancient lenses on display in the Archaeological Museum at Herakleion, and many more are in storage there,” write George Sines and Yannis A. Sakellarakis in "Lenses in Antiquity" (1987). “The use of lenses [in antiquity] was widespread throughout the Middle East and the Mediterranean basin over several millennia,” they conclude, “[and] the quality of some of these lenses was sufficient to permit their use as magnifying glasses.” (1)


One of the most famous lenses from antiquity is the “Loupe of Sargon” (above, 750-710 BC)--also known as the Layard Lens or the Nimrud Lens--a rock-crystal lentoid excavated by Austen Henry Layard at the Assyrian place of Nimrud (present-day Iraq) in the 1850s. On display in the British Museum, this lens is thought by some to be a burning-glass, used to focus the sun's rays to produce fire. Others claim it is a magnifying glass or part of an ancient Assyrian telescope. “Experts on Assyrian archaeology are unconvinced,” claims Wikipedia, “doubting that the optical quality of the lens is sufficient to be of much use.” (2)

Burning-glasses were known in the ancient world. Aristophanes refers to "the beautiful,
transparent stone with which they light fires" in his play The Clouds (424 BC). Pliny the Elder (23-79AD) describes how glass balls filled with water could set clothes on fire when placed in line with the sun. Both Pliny and Seneca the Younger (3 BC-65 AD) also describe the magnifying effect of a glass globe filled with water. However, the poor quality of lenses from antiquity has led some scholars to conclude that “Bronze Age and early Greek finds do not warrant an unequivocal interpretation as optical tools.”

“Some of the examples from Knossos still preserve their original backing foil,” writes Dimitris Plantzos, in “Crystals and Lenses in the Graeco-Roman World” (1997), “which suggests their use in inlay. ...Their excellence in material and workmanship enhances their decorative appeal. At the same time, their imperfect surfaces limited their potential use as optical aids since they would distort the magnified image. Even nominal magnification as high as 10x or 20x, as estimated for some examples (but considerably lower in real terms), would not, considering the serious distortion of the lens, be enough to aid in producing miniatures. The most famous among the objects identified as antique lenses is the so-called ‘Loupe of Sargon.’ The object is oval (40 x 35 mm) and of uneven thickness (max. thickness 22.5mm). Its focal length has been calculated at 112.5 mm. Its nominal magnification is about 2x but, owing to its imperfect surface, it would be useless as a tool.” (3)

Some 5^th-century-BC lenses, such as those discovered in a cave on Mount Ida in Crete, in 1983, can magnify with perfect clarity up to 7x, but Plantzos argues that crystal lenses were primarily used as burning-glasses, game pieces or decorative inlays. Their use in aiding vision, he cautions, was limited. “Philosophers and scientists accepted vision as the free movement of visual rays through a transparent medium like air or water, and attributed the empirically observed magnifying properties of lenses and crystals to their transparency rather than their refractive quality. This perspective explains why Seneca's observation that ‘lenses’ could improve vision did not find a practical application [until the 13th century].”


Is the magnifying glass in Sir Lawrence Alma-Tadema's painting pure fantasy? "The body of evidence for the production of lenses in antiquity is... meager and dubious," Plantzos concludes.

Notes

1. Sines, George and Sakellarakis, Yannis A. “Lenses in Antiquity.” American Journal of Archaeology, Vol. 91, No. 2, April 1987, pp. 191-196.

2.Wikipedia. “Nimrud Lens.” 2012. http://en.wikipedia.org/wiki/Nimrud_lens

3. Plantzos, Dimitris. Crystals and Lenses in the Graeco-Roman World. American Journal of Archaeology, Vol. 101, No. 3 (Jul., 1997), pp. 451-464. http://www.hist-arch.uoi.gr/prosopiko/plantzos/Crystals.pdf