Stereoscopic Microscopes and Coins

A Useful Tool or a Fun Toy

A recurring theme of the pages that make up this site is the desirability of looking closely at our coins. Usually this involves being aware of minor details of coin design, style or fabric. Collectors, as with all people, are greatly different one from another. A few become skilled in the hobby combining sharp eyesight with great practice in interpreting what they see. There is no substitute for practice; there is no shortcut that can replace 'experiencing' thousands of coins. Eyesight, however, can be aided. Many collectors carry a small pocket magnifier to correct the loss of near vision most of us experience with age. This page will discuss going a beyond these low power glasses and looking at coins in a way that we have not seen them before. Using a microscope we can examine small details that would escape the notice of the unaided eye. These enables even those of us with less than perfect eyesight to see details we might have missed otherwise. What is to be seen in this manner can be both educational and beautiful.

Common laboratory microscopes consist of two optical components that together determine the degree of magnification. The lens near the subject, the objective, projects its image up the tube of the microscope where it is further magnified by the eyepiece. A 5X (five power) objective and a 10X eyepiece combine to present a 50X image to the eye. For most uses in numismatics this is too much magnification. Even microscopes with three objective turrets tend to offer choices that are all too powerful for examining coins. My old (Leitz from the twenties? - a flea market find) scope shown here came equipped with 5X, 10X and 45X objectives. I replaced the 45X with a 2X from another old scope which is the choice for 95% of my needs. The scope was intended for use with light transmitted through the subject (slide) rather than with three dimensional objects by reflected light. It was necessary to cover the hole in the stage with a piece of felt that serves both as a background and as a means of adjusting the position of the coin by sliding across the stage. Light can be provided by a small, high intensity light ('Tensor') or simply by working in the sunlight. When using a camera for photos through the microscope, it is possible to omit the eyepiece and obtain a lower magnification.

What can you see through a microscope? This question is not all that simple. I wish I could tell you that there were obvious signs that would enable the user to separate the fakes from the genuine or some other matter of great interest but the truth is less spectacular. Often what you see are hints of how the coin was made and what has happened to it over the years. The difference between a naturally smooth surface and one that has been polished on a buffer can be the difference between scratches with random direction and grooves all following a pattern. Our example shows a "minor type" of Pegasus in the field of a drachm of Alexander the Great. The design is cut in a shallow recess below the plane of the rest of the field. There is a general graininess to the surface. Does any of this suggest the coin is real or fake? I do not know enough to answer this question but I have filed the appearance of this detail in my memory so I can recall it when I see something similar. This Pegasus is the work of the modern Bulgarian copyist Slavey. What you see here is a fake.

Our second example is a relatively infrequent example of a use of higher magnification (50X here). We see a tiny section of the flat field of a sestertius of Caracalla. The coin has no patina but has been polished (note fine scratches) long ago and is retoning. Details of the metal alloy are revealed. Combining two or more metals produces different mixtures according to the metals and proportions used. Some will combine in an even alloy; other metals clump with pockets of one being surrounded by others. Third century bronzes often contained a good amount of lead. Lead pockets are shown here as gray areas surrounded by the copper and other components. Had this coin been subjected to harsh chemical cleaning or very high heat, the (relatively delicate) lead would have been eaten away. I have seen coins heated with a blowtorch to the point that lead bubbled out of the coin. Since the heat of the torch was not enough to melt the rest of the coin, the result was a porous skeleton with ugly pits where the lead had been. Proper metallurgical examination of a coin would require destructive cleaning and polishing of a freshly cut surface. This photo is just an example what can be seen in some cases with no such preparation.

The preceding discussion considered the use of a standard laboratory microscope of the type that many of us have used and may have hiding in a closet. There is, however, an instrument 1000% more suitable for use by the coin collector: the stereoscopic microscope. A stereoscopic microscope is actually a pair of relatively low powered scopes that retains the three dimensional view of the world afforded to humans with two eyes. If you are blind in one eye, there will be no benefit in using a stereoscopic microscope; if you have normal binocular vision, a whole new world is awaiting your discovery. Most of us never see close things in 3D. When we look closely (using a lens or with the unaided eye) we close one eye and receive a flat image. The principles of stereoscopy were discovered at about the same time as the invention of photography (1839). Early photographers combined these two discoveries and recorded their world in three dimensional photographs. People of that era enjoyed looking through a stereoviewer that delivered the right image to the right eye and the left image to the left. Most people never consider that seeing the world in 3D is the result of two different images from eyes set very slightly apart. The effect was like magic. After nearly a century of popularity the fad wore off and people tired of having to use a viewer when looking at photographs. A new fad, the motion picture, took over and stereo views were left to a minority (myself included) who find them fascinating.

The following photos are two stereoscopic pairs. To view the images in 3D, it is necessary to cause the right eye to look only at the right image and the left eye only at the left. This can be done without a viewer by moving the eyes outward (wall-eyed) until you see three images of each coin. The center image (if all is level) will converge into a three dimensional photo. Some people can view these images easily with no viewer; others try and try but never quite succeed. Each person develops their own little trick to make it work. Looking 'through' the images at something far away and moving the images into view sometimes helps. I have been looking at stereo images by 'freeviewing' for so long that I am at a total loss for words that will enable you develop the technique. Just try it.

I have chosen to present these images in the format popular in the last century (left on left; right on right) but some people find them more easily viewed if they are reversed and the eyes are crossed to fuse the pair. I have never been able to succeed in viewing images in crosseye format but I know people who can only do it in this way. I believe it is mostly a matter of which way you learned first seeming natural. Crosseyed viewers among you may need to download the above images into your graphics program and reformat them or just take my word for it: 3D coins are neat! It is nice to be able to photograph in 3D but simple direct viewing is certainly enough and much less trouble. The micro-stereoscopic world is filled with the same magic that attracted the Victorians when photography was new.

Format considerations are a problem only in showing photographic images but not when using a stereoscopic microscope. Still there is a bit of preparation and practice needed to get full benefit from the device. Each user must adjust the scope for fit. This is accomplished by closing the right (usually) eye and focusing with the main mechanism using only the left. Then, closing the left, use the separate focus for the right eye. The space between the eyepieces must be adjusted until one circle of image is seen when looking through the scope with both eyes. This setting will be different for each user since the space between the eyes varies greatly from person to person. Failure to make these adjustments will prevent proper images being delivered and reconstructed in the brain as a single 3D image. My scope is a cheap (under $200 new on eBay) Chinese product. I have used Leitz scopes that cost many times more and admit the more expensive scopes are a little better. For the money, my scope is amazing. There are many low priced brands and variations available. I have looked through a few brands and can not say I see a great difference. Buy either a scope you have tried or one that has a return privilege just to be safe. If you have access to a scope at work or school, try looking at a coin. You might decide that you need a new toy.

Standard technique requires the coin be placed flat on the stage and viewed using the built in fluorescent light. Some uses may require adding more light from the high intensity lamp mentioned above. Working in sunlight can be good if you have a place with security and remember to use sunblock. ;) I find that covering the glass stage (the scope has transmitted light also - a feature I never use) with a black pad cuts down flare from light on the white stage and allows easy adjustment of coin position. My scope came with 1X and 3X objectives and 10X eyepieces providing a choice of 10X or 30X images. Other scopes are offered with 20X and 40X options. I advise that the lower power will be most used and 20X is too much for some coins. Don't buy the more powerful unit thinking bigger is better. Consider what you will be viewing and buy accordingly. Most scopes allow photography through a camera adapter accessory but taking 3D images will require these to be paired. Stereoscopic photography is a subject for a thick book, not my little amateur web page. The example in this paragraph shows two magnifications of detail from the reverse of a denarius of Septimius Severus. The coin has a dark tone and scratches consistent with handling more than abrasive cleaning. We see Salus holding a snake composed of a row of dots. The snake is being fed from a patera held just under its head. The detail on the head includes an eye, beak and topknot that strikes me more like Woody Woodpecker than any snake I ever met. Remembering that the snake head is less than one millimeter across, I think we can forgive the diecutter for taking liberties with the design. These two images show two different magnifications. Some details are more easily seen in the larger one but others are more clear at a lower power. The manufacturer of the scopes gives you a choice of powers exactly for this reason.

A modified technique for using a stereo microscope has been found useful to me. Using the lowest power (10X) hold the coin on edge and focus the scope on the top edge of the coin. Rotate the coin so you can examine all sections of the edge while maintaining clear focus by steadying the coin on the (padded) stage. You will be surprised what you may find on those edges. The obvious thing would be to look for seams or file marks that might bring question on the authenticity of the coin. (Please remember there are MANY reasons a coin can have a seam or file marks other than being fake!!!! We have even discussed one of them on this site's page on fabric). After completing the look at the edge, pick up the coin and hold it at a level of sharp focus. Move the coin around slowly tilting it several ways. Focus by moving the coin up and down rather than using the controls which you preset when looking at the edge. Let the light shine into different parts and see how the image changes with the angle of the light. Many coins will show nothing particularly of value over the standard flat examination but the ones that do can be quite interesting. The technique is particularly effective when looking at coins with cracks, test cuts or centration dimples that might be hiding information in the shadows. Still photography reveals much less data than a coin being wiggled under a stereo microscope.

What can we tell from what we see? You may see residues of cleaning materials or brush fibers stuck in cracks. Tiny broken bits of brass or yellow plastic may tell you how the coin was cleaned. Fine red fibers usually mean the coin spent some time in a flocked tray (many of my coin photos show this unless I remembered brush them off before shooting). I wish I knew all the things I am seeing here but I am just a beginner at this. Interpreting what you see is not the easiest subject you could tackle. Be careful to store away in you memory what you see and, in time, it may start to make sense. Future pages on this site will probably include more images as I learn to read the details revealed through the microscope. I certainly hope some of them will be more significant than identifying red lint but remember that everything you see needs to be considered carefully and not everything will be signs of serious problems. While looking at the red fibers in this photo, did you notice that the coin is fourree? Keeping open eyes and an open mind to what we see will prove to be a more important tool than the microscope itself.

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(c) 1999 Doug Smith