New protocol for old microscopes...

As he continues his journey into the lost world of the Leeuwenhoek microscope...Brian J Ford asks, just how many genuine examples are there?   

How many genuine Leeuwenhoek microscopes exist? The standard accounts say there are nine, though one extra example (which had laid for years in a cupboard in Leiden) brings the total to 10. But – and this is the crucial point – how do we know? How could we tell for sure? As with oil paintings by the great masters, we rely on the look of an object, its compatibility with reference examples of known provenance, and the opinion of experts in museums. None of this gives us certainty.

Recently I have been asked to appraise several Leeuwenhoek microscopes. Most are easily identifiable as fakes, but two seem to be genuine (Laboratory News, February 2015). One is made of silver and was brought into an auction house in London. Following my examination of the little microscope, it was privately purchased and I outlined my conclusions to its new owner when we met in Cambridge. My findings have since been substantiated by the Boerhaave Museum in Leiden, where many Leeuwenhoek microscopes are held.

The second example is a brass microscope that emerged from the canals of Delft, where Leeuwenhoek lived and worked, and was advertised through eBay. It was heavily discoloured after centuries of burial in mud. Everything about this one similarly suggests it to be genuine, indeed, there is a very similar microscope in the Leiden collections.

Yet still we were largely relying on opinion. The scientific evidence we had, including analyses of the metals used to make the microscopes and hall-marks impressed into the surface of the silver, were inconclusive. Valuable artefacts are often forged and hallmarks can be faked. Dr Gary Laughlin, Director of the McCrone Research Institute in Chicago and an expert on forgery, added: “If I wanted to take a shiny, brass and glass object and make it oxidise and darken without producing the usual copper patina of malachite/azurite, I might easily slosh it around in a cup of water with selenium oxide and instantly have anaerobic-looking dark copper patina.” Similar comments came from Sir Alan Fersh FRS, master of Gonville and Caius, my college at Cambridge and an authority on forgery in clock-making. He informs me: “The top restorers make brass screws by the 17th century method of using a screw plate, and forgers melt down brass candlesticks to obtain brass of the correct composition.”

[caption id="attachment_47162" align="alignleft" width="300"] A Leeuwenhoek design of 50mm-long microscope dredged from canal mud in Delft, Netherlands. It has all the appearance of a genuine microscope made around 1690.[/caption]

Analytical data alone are clearly insufficient. We need something more, and I decided to use a novel approach. It seemed to me that the fine details held the truth. Professor Richard Langford is head of the microscopy suite at the Cavendish Laboratory of the University of Cambridge and was kind enough to allow to use scanning electron microscopy for a close examination of the way the brass microscope was made. I was anxious to use low-power magnification, and the advice of my scientist colleague Jon Rickard at Cambridge was to use their Hitachi S-3400N variable-pressure instrument.

Thus we embarked on an extensive programme of something new – scanning electron macrography. For the first time we could step through the limits of conventional the close-up photograph and discern the finest details of construction. First I studied a replica microscope, which looks to the naked eye very like the original article, and then compared these images with studies of the microscopes dredged from the mud of Delft. The spherical positioning control of the replica microscope has cast marks that betray its origins; the Delft microscope is clearly hand-finished. The specimen pin in the replica shows it has been turned on a lathe, whereas the Delft microscope pin has a faceted structure showing it to be hand forged. The screw thread of the replica clearly shows die marks with many subsidiary scratches around the thread, while the brass microscope from Delft has thread with an unusually square profile.

[caption id="attachment_47163" align="alignright" width="300"] Replica Leeuwenhoek microscopes like this have been made for years at the Boerhaave Museum in Leiden. They are marked to prevent being considered genuine.[/caption]

Held in the hand, these two microscopes look remarkably similar yet the SEM reveals marked distinctions. This shows that the two microscopes were made in disparate ways and by different craftsmen. It does not substantiate genuineness. We now need to embark on a lengthy programme of microscopy. Several of the surviving Leeuwenhoek microscopes are documented from source, and there is no doubt about their authenticity. Do these too have forged specimen pins, and hand-worked positioning knobs? Is the hand-cut thread of a similar profile? These are the signs that alone can reveal a given microscope to be genuine or a forgery. Of those known to exist, several lack a paper trail and can be doubted – but the use of scanning electron macrography can give us the facts we need.

With the 10 Leeuwenhoek microscopes in collections, these two new examples could bring the total to 12. Only when this research is complete can we know for sure how many actual Leeuwenhoek microscopes exist. My guess is that, in the final analysis, the number of genuine examples will be fewer than we realise. It is the SEM that holds the answer.