One of the many things you should have as a gemologist (or even a jeweller) is access to higher magnification. While a loupe is sufficient for a lot of things like clarity grading or quick referencing, sometimes you may need more in order to observe smaller inclusions or subtle growth marks in a gemstone.
The reason why gemologists need to use magnification to view such tiny or mild interior characteristics is because much of the evidence used in gem identification is not be readily seen by the loupe or the human eye. These could be gas bubbles, curved striae, flux inclusions or a number of many other things that dictate the true identity of a natural, synthetic or treated gemstone.
Most laboratories have at least one gemological microscope, either a standard binocular one or a trinocular one (with a tube for the camera) that can zoom to about 40x or 64x. This is essential for better capabilities in inclusion observation for all gemstones.
Now, the microscope is made up of different parts. We have the head, which is usually where the optics system is held. This would be a series of mirrors and lenses that link the objective lens to the oculars so that you can view a larger image of your item. Many people would probably say that the head is the most costly section of the microscope to replace.
Most Gemologists' Favorite Instrument is the Binocular Gem Microscope, as It Allows Them to Immerse Themselves into a Miniature World of Crystal Inclusions, Vibrant Reflections and Opportunities for Deductive Identification.
The objective lens is the lens that is closest to your item, while the oculars or eyepiece lenses are those that are closest to your eyes. Aside from these, the microscope head also usually hosts a know or two. One knob is called the focus knob, which allows you to sharpen the visual field you see, while the other knob would be for zoom magnification.
Most gem microscopes use a rolling zoom capability where turning the knob creates a gradual zoom. This is unlike other microscopes from industries such as microbiology where multiple ocular lenses are used for different magnification powers.
The placement platform is beneath the microscope head, and this is where the gemstone clip holders are usually set. Someone using a pair of tweezers to grasp a gem would also want to rest them on this surface for steadier viewing.
The microscope's iris diaphragm is situated below where your gem would be positioned. This part allows you to manually limit the amount of light you need for illumination. Another similar part is the baffle, which is a small cover that can be used to switch your set up from brightfield to darkfield lightings.
The electronics of a microscope are usually housed in its base. This area also houses the light well or light source, where the main bulb is positioned.
The microscopes used in gemological laboratories also employ 5 different types of lighting modes. Each one used for specific purposes in the deduction of gemstone identity.
1. Darkfield illumination - The microscope's "baffle" (cover beneath the gemstone placement area) is closed, allowing light beams to enter the gem from its sides instead of directly from the bottom. This method of illumination allows us to see a gem's interior characteristics much better. Most inclusions will be lit well for observation, even smaller ones that might have been missed if viewed in normal lighting.
2. Brightfield illumination - The microscope's "baffle" is open, allowing light to pass freely through the gem and into your eyes. Many use this mode in conjunction with a partially open iris diaphragm (circular opener above the baffle that looks like a camera shutter). This is to limit the amount of light that is let out from the light well.
3. Reflected light - This makes use of an external overhead lamp that usually emits daylight-equivalent or fluorescent light. It's often used for viewing the surface condition of gemstones or for evaluating the nature of any fractures and blemishes present.
4. Fiber optic illumination - This type makes use of a fiber-optic tube attachment or an external fiber-optic lighting machine. It allows you to direct a focused beam of light (sometimes cold light) at any flexible angle, in order to view specific parts of your gemstone's interior.
5. Diffused illumination - Here, you would normally use either a diffusal plate, translucent white plastic or even a sheet of paper to manually diffuse the light coming out from your microscope's light well in brightfield mode. This particular setup is good for viewing subtle zones of color, such as those often seen in synthetic blue sapphires or lattice diffused corundum.
A microscope is very useful for many various reasons, and a good gemologist knows how to use one to its full advantage. Such a tool is ever-present amidst the scientific suite of instruments you will find at a gemological laboratory.
