Learning Library

Dark Field Loupe

A handy tool for indentifying coloured gemstones.


Firstly, despite its appearance the dark field loupe lights a gemstone from the sides and not from underneath. This might first appear strange, as the torch supplied with your dark field loupe fits into the bottom of the device and appears to be pointing light underneath the gemstone. Once assembled and the torch has been turned on (make sure your batteries are fully charged because you want as strong a light as possible), you look through the 10x magnification eye piece to study the gem.

The main difference between a standard loupe and a dark field loupe, is that with the latter you are viewing the gemstone with a controlled light entering just from the sides of the gem and the background colour is black – the ‘dark field’ of a dark field loupe. This lateral illumination will make it easier to study a gem’s inclusions than a standard loupe. A nice analogy I heard was if you are lying in bed and there is a crack in your curtains on a sunny morning, you will be able to spot dust particles in the beam of light (dark field), but you would not spot them if you faced the light head on (bright field).

As always, be sure to fall in love with your gemstone before using the loupe, as once you study any gem under magnification, it will only diminish your love affair. It’s crucial that Gem Collectors are appreciative of the immense traumas gems have to endure during their millions of years in creation in order to maximise the pleasure of the hobby! However, being able to spot inclusions easier is important for being able to identify and distinguish one coloured gemstone from another.

To use the loupe, hold your gemstone or piece of jewellery with tweezers and slowly rock your gemstone backwards and forwards. If the gem looks out of focus, as you would with a normal loupe move it towards or away from the eye piece. The first time I used a dark field loupe I thought the gem had to sit in the well so that the light was delivered into the gem perfectly from the side, but if you do this you will never get it in focus.  

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Steve using a Dark Field Loupe.