Gemologists rely heavily on a very particular kind of microscope for their work in identifying and evaluating gemstones. There are a few specific features that allow a gemologist to observe inclusions, fractures, and striae that might otherwise go unnoticed. The microscope must possess not only sufficient magnification power to reveal flaws and inclusions within a stone but also offer different illumination options to help highlight internal features that would not be visible otherwise.
Below are some key qualities to consider when selecting a gemological microscope:
1. Magnification Power
In day-to-day gemology, and for basic details on a stone, a 10x magnification is generally adequate. To a working gemologist, this is provided by a standard jeweler’s loupe. Actually, this is also what defines the term “loupe clean” that is used when qualifying the clarity of a stone. However, the whole point of having a microscope is to see a bit more detail and most gemological microscopes will offer magnification of at least 40-45x to inspect the internal structures of a gemstone. The extra detail that would not be discernible with the naked eye or even a jeweler's loupe can help a gemologist figure out the identification and sometimes even the origin of a gemstone. Generally, a good gemological microscope will offer a higher magnification of 60x to 90x. Anything higher that 120x is unnecessary, so compared to some microscopes out there, the optical requirements are not too extreme. A larger microscope will typically allow a user to zoom in as opposed to the typical science-class microscope which will have three different objective lenses in a rotating turret. On a portable gemological microscope, there will not be a zoom facility. In this case, higher magnification can be achieved simply with a second set of eyepieces that offer a 2x increase on the basic 40-45x.
A defining feature of a gemological microscope is darkfield illumination, it is identifiable by a light that is set in the base under an adjustable iris. Interestingly, this was patented by Robert Shipley Jr. in 1939. He was the oldest son of the founder of the Gemological Institute of America and made a few contributions to the field of gemological instruments. Darkfield illumination is when oblique, reflected light illuminates a gem against a black backdrop. Inclusions and other imperfections scatter this light, making them appear as bright objects against the dark background, whereas in normal direct illumination they would not have been visible. Dust and scratches may also scatter light, causing them to become more noticeable.
A gemological microscope will also offer brightfield illumination, which is beneficial for examining specimens with different color zones or for concealing dust particles and scratches. For those capturing images of gemstones, having both options is crucial for presenting the subject in the best possible manner.
- Brightfield illumination involves shining light directly into the gemstone from below. This method is useful for examining color zones or growth zones, areas of different colors, and low relief inclusions. It's also effective when scratches or fine dust particles obstruct proper darkfield inspection.
If you intend to photograph your gems, having both types of illumination will allow you to accentuate a gem's best features while concealing its flaws selectively.
3. Top Illumination:
In addition to the adjustable lighting options provided from directly under the object, there will normally be at least one other option on a small ‘travel’ microscope, and usually two on a full-size microscope. This provides what is known as top illumination and this is overhead, side or oblique lighting. This is used for inspecting external features like polishing marks, pitting, and other surface blemishes. Correctly positioned to allow a view of the surface of an object, we can also see luster differences that would identify glass-filled gemstones or glass-topped doublets.
It also enhances coverage and visibility of the gem's surface during examination, offering a good representation of how a gem or piece of jewelry will appear under normal indoor lighting conditions.
On a travel microscope the top illumination is generally provided by a lamp sitting at the junction of the head and neck of the microscope. On a full-size microscope, there will usually be a tilt-adjustable lamp with daylight fluorescent tubes to provide a general illumination. Sometimes there is a built-in fiber-optic light with an adjustable gooseneck, but often a good microscope is better served with a stand-alone fiber-optic lamp.
4. Trinocular Head:
Gemological microscopes have binocular heads meaning there is an eyepiece for each eye and a viewer gets a ‘stereo’ view. While it is possible to find attachments that allow you to secure a camera to one of the two eyepieces, it is possible to get a trinocular head. A trinocular microscope head features a dedicated eyepiece for attaching a camera.
This is the ideal choice for serious photography enthusiasts in gemology. The art of taking pictures through a microscope is known as photomicrography and a student gemologist will be increasingly drawn to it as they learn and appreciate more about the internal and external structures in gems and minerals.
Proper accessories are essential for securely holding, manipulating, observing, and photographing gemstones. Depending on your specific requirements, you might also need accessories capable of accommodating stones of various sizes as well as jewelry, such as rings. A stand that tilts and rotates makes the viewing process more convenient by allowing the user to move the microscope to suit their seated position thereby reducing fatigue.
There have been few changes in the fundamentals of a gemological microscope in the last 90 years, but one noticeable development is the increased use of LED lighting. Adoption has been slow because LEDs do not yet perfectly mimic the relatively clean spectrum of an incandescent light bulb, but they are a lot closer now than they were ten years ago. For many gemologists who work for extended periods with a microscope, the heat that comes off a base burning incandescent bulbs is unpleasant. While a lot of older microscopes can be upgraded to LED lighting, this is costly and only certain models are compatible with the upgraded bases.
In your quest for the ideal microscope, dealers typically offer a range of gemological microscopes to cater to your specific needs and budget and the second-hand market is strong. Buy the best you can afford because a good microscope will last for most of your career and some of the incredible things you get to look at will pass through your hands, never to be seen and appreciated by you again. You want that memory to be of a pin-sharp image that is perfectly illuminated!