Catching the Afterglow - Taking Pictures of Phosphorescent Minerals
Many minerals exhibit an “afterglow” when the UV light is turned off. This glow can last for milliseconds or hours depending on the mineral. Some are very bright while others are barely perceptible. Examples of minerals that are well-known to often be phosphorescent include:
Franklin calcite – has a BIP (brief intense phosphorescence, lasting perhaps less than ½ second)
Terlingua calcite – very strong blue phosphorescence
Fluorite – many varieties, especially those from the Midwest states such as Ohio
Willemite – many pieces from Franklin, NJ, as well as from the Puttapa Zinc Mine in Australia
Tugtupite from Greenland
Sodalite from Afghanistan, and many, many more
Willemite and Calcite – Puttapa Zinc Mine, Australia, under Shortwave - Phosphorescent
At least three different phosphorescent colors are present in this specimen. Some are very brief and are really only revealed in a photo – your eye is often not quick enough to register these colors.
Taking a picture of phosphorescence requires a good camera, special camera settings, and lots of luck. I use a Nikon DSLR and have reasonable success. Most point and shoot cameras or smartphones will not be able to take acceptable phosphorescent photos because they do not have the low-light settings. But some may – just play around using the techniques shown here.
Phosphorescence is usually a relatively short, dim “glow”. Your camera must be set to capture this dim subject. The first requirement will be a completely dark shooting environment. Your camera will be set to capture any light in the room and a little bit of ambient light might ruin the photo.
The camera must be set to capture low light images (and of course on a tripod). This usually means setting the aperture to a wide open f-stop (I use f4.5) and shooting with a high iso (I usually shoot with iso500). But these both have drawbacks. Lower f-stops reduce the depth of field and high iso’s result in noisy (grainy) images. Find the best compromise between an acceptable shot and focus/noise.
I use a time exposure of around 2 seconds. Very few minerals exhibit significant phosphorescence longer than that so any longer setting just increases the chance of picking up ambient light.
These settings are guidelines and may differ with your camera. Non DSLR cameras may not even have settings for iso, f-stop, or even time exposure. The quality of your photo will then depend on how good that camera is with low-light situations.
Now comes the luck part. After you’ve got your settings optimized it’s time to take the photo. The trick here is to synchronize the opening of the shutter with the moment the UV light is turned off. I sometimes have to take 3 or 4 shots to get a decent capture. One trick I’ve learned is to turn on the exposure delay setting on the camera (if you have it). Many DSLRs allow you to delay the opening of the shutter for a second or two to allow the mirror to stop vibrating after it is flipped up. I also turn on the camera sound effects. With practice you can then use the noises coming from the camera as a sort of “1-2-3-go” and switch off the UV light at almost the exact moment the shutter opens.
Your results will vary. The shot I show above of a beautiful piece of Puttapa willemite calcite shows multiple phosphorescent colors (compare to the SW pic). In this shot I was really lucky in my timing and even captured the very brief phosphorescence of the calcite (lasts for less than ½ second). Puttapa pieces have exceptional phosphorescence – often with multiple colors, some very long lasting.
There surely are other techniques I can imagine to take a more precise and controlled image. Motors and shutters to alternately block the UV light and open the path to the camera lens for one. But setups like that would be very complex. This is a quick and dirty way to capture acceptable shots.