A version of this article was originally published in the CREG Journal #105 - a publication which focuses on the application of technology in cave exploration and study. To learn more, click here.
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| Photographing Fluorescent Minerals |
One of the largest deposits of fluorescent minerals can be found at the Sterling Hill Mine in Ogdensburg, New Jersey. William “Lord Stirling” Alexander, the owner of the mine, oversaw the first extraction which began sometime around the 1630s when he mistook the site for a large cuprite deposit - an ore of copper. However, the site actually contained red zincite, which was an unknown mineral at the time and is rarely found in nature in its crystal form. After Lord Stirling’s unsuccessful copper mining attempts, Sterling Hill found little use until the War of 1812 when zinc was extracted for brass, leading to the formation of the the New Jersey Zinc Company (known today as the Horsehead Holding Corporation). It was not until 1818 when local mineralogist Samuel Fowler acquired portions Sterling Hill that its geological and economical importance became evident. Fowler helped attract the eager attention of the scientific community. Sterling Hill would end up operating as a zinc and iron mine until 1986, when the New Jersey Zinc Co. decided to close its doors over unpaid back taxes. Over 35 miles of tunnels were abandoned, spiraling down around 2,000 feet below the surface of the Earth. Sterling Hill reopened as a museum in 1990, and only the top 100 feet remain unflooded and accessible to visitors.
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| Some of the original mining equipment |
The Zincite found by Lord Stirling in 1630 led me to Sterling Hill for the first time about a year ago, camera and tripod in tow. However, I didn’t go just for the zincite itself. I was instead seeking its common associations, calcite and willemite, which are known to fluoresce a vibrant orange-red and green under ultraviolet light. Admittedly, I did not know these species by name at the time, I just knew them by their hypnotic color. Both longwave and shortwave UV light will produce different hues in calcite and willemite, but in either case, the result is a magnificent bloom of color. The once unassuming rocks transform into a dazzling display of multicolored-light.
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| Fluorescent Minerals in White Light |
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| Fluorescent Minerals in Shortwave UV |
Many of the minerals found in the Franklin/Ogdensburg area feature another mesmerizing characteristic, phosphorescence, which is a type of photoluminescence related to fluorescence. A species is defined as phosphorescent when it does not immediately re-emit light that it is exposed to. Phosphorescent species may not be as bright as their fluorescent cousins, but they emit light on a slower time scale, so they can often be found illuminated long after the original light source was removed. Large calcite flowstones at Sterling Hill will phosphoresce a neon green under both longwave and shortwave UV.
What makes the Franklin area a hotbed for fluorescence? The answer lies in the geochemical complexity of the site and the 1.3 billion years of geological events that led to the formation of over 370 minerals. Many minerals require an “activator” that allow them to emit light. In the Sterling Hill orebody, manganese (Mn2+) is the activator that enable many of the species to fluoresce. There are some minerals, like powellite (CaMoO4), that can fluoresce on their own without the need for an activator. In the case of powellite, the MoO4 group causes the fluorescence and is fundamentally a part of the chemical composition.
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| Calcite Flowstone under White Light |
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| Calcite Flowstone demonstrating Phosphorescence |
Photographing fluorescent minerals is a lot like night photography. In both cases, there is little background light to work with. Additionally, both night photography and mineral photography share a common technique called light painting, where a light source is moved during a long exposure to “paint” certain areas of a scene with light. Because the camera is continuously capturing light while it’s exposing, the finished product is a photo where all the desired elements are lit. This is not only required because the light from the UV lamps tends to fall off rather quickly (see inverse-square law), but also because the lamps required to light the scenes can be very expensive. Longwave lights are considerably cheaper than shortwave and will produce wonderful color in certain species. However, the most intense colors are usually seen under shortwave lights, which are of a higher cost. One benefit of using longwave UV is that it is available as an LED torch, which travels a much greater distance than the classic shortwave bulbs, making them ideal for light painting.
Great care should be taken when using ultraviolet lights. Much of the light they emit cannot be seen with the human eye, but that does not mean they aren’t dangerous. Think of spending time under a UV like spending time in intense sunlight. You can receive burns and eye damage. Proper personal protective equipment such as safety glasses should be worn.
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| Using portable shortwave UV lights |
Here is the equipment I used:
- Large aperture, wide angle lenses (f/1.8 - 3.5 are acceptable)
- Canon EF 28mm f/1.8 USM
- Sigma EX Fisheye 15mm f/2.8 DG
- A solid tripod
- Manfrotto 550
- DSLR
- Canon 6D Full Frame
- A way to trigger the shutter without moving the camera
- Built in two second timer
- Ultraviolet lamps
- One (1) Convoy S2+ UV LED Torch (365nm Longwave)
- Two (2) Way Too Cool 9 Watt Dual (254nm Shortwave)
- Five (5) UV Systems TripleBright Permanent Fixtures (254nm Shortwave)
- A white light source
- 1000 Lumen Waklyte S116A LED Torch
- Photo Editing Software
- Adobe Lightroom
The steps for each shot are roughly the same. I first find my desired composition (subject placement, framing, and focal point), and then decide what specific sections of minerals I would like properly exposed. All the decisions up to this point are purely artistic. Then, my camera’s built in light meter is used to determine the brightest point in the image to ensure that it doesn’t overexpose. Shooting in RAW helps me recover any sections of the photo that might be slightly over/under exposed later on in post processing. I try to use a lower ISO to decrease the amount of grain, and I tend to use a larger aperture to compensate for the loss of brightness from the low ISO. Using the white light source, focus is set, and then either myself or an assistant will shine the UV lamp over the predetermined path as the exposure begins, painting the scene as planned. Because this exposure is generally seconds long (5 - 30 seconds), and because the minerals are so bright, the lamp-wielding assistant can travel in front of the camera while the photo is being taken as long as they move quickly. They should be invisible in the final image. Once the shutter has closed, the image is reviewed. If there was any error in focus, or lighting of the minerals, for example, the necessary adjustments are made and the shot is retaken.
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| A tunnel which has been captured using light painting |
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| Assistants waving UV lights moved rapidly down the tunnel during the exposure |
If the shot contains elements that do not fluoresce (such as a human subject), the procedure is almost identical, except the bright white light source is used at the beginning of the exposure to illuminate any non-fluorescent elements. If the shot contains a human subject, it can be difficult for someone to stay perfectly still for upwards of 30 seconds, but by using a bright light source as described above, the initial blast of white light acts as a flash which helps freeze the motion of the model.
The final step in the photography process is post production. Below, there are two chromaticity diagrams. The one on the left represents the full visible light spectrum, or what we can see with the human eye. The one on the right indicates what colors are displayable on a modern computer monitor using the RGB color model.
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| CIE 1931 Color Space Chromaticity Diagram (Source: Wikipedia) |
Herein lies the main issue with trying to accurately capture the true color of a fluorescent mineral: it is simply not possible with our current technology. The exact colors of many species can only be seen with our eyes. Therefore, in Lightroom, I generally increase the vibrance, but I don’t worry too much about obtaining a perfect representation. I mainly try to decrease the highlights and increase the shadows in the image to restore as much detail as possible. Additionally, because I did not shoot with a UV Filter, some of the excess UV light reflecting back towards the lens may have added a blue color cast to the image. Adjusting the white balance can help reduce this effect, or success may be found in split toning the highlights using a warm color.
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| Minerals displaying a wide array of colors |
I would like to thank Dr. Earl Verbeek for sharing his knowledge of the Franklin orebody with me, William and Denise Kroth for giving me photo access to the Sterling Hill mine, and Patrick Bigos for letting me use his UV lamps. I would also like to thank the team that helped me photograph the minerals (Theresa Kucinski, Anissa Bailis, Celina Bailis, and Ivan Gonzalez) and Jennifer Latchford for editing this article.