Adventures in Ultraviolet Light photography

I’ve always known that many things react to ultraviolet (UV) light, including various natural organisms and minerals. However, it wasn’t until recently, after being inspired by my friend Ágnes Berentés, a Hungarian cave photographer and geologist, that I decided to explore the fascinating UV reactions I could find and photograph in some caves in the UK. Ágnes has produced incredible work photographing caves and mines all over the world using ultraviolet light, and it was her work that motivated me to see what I could discover myself.

Caves are particularly good places to find UV-reactive minerals. Calcite-based minerals, such as calcite itself and other carbonates like aragonite, often show fluorescence or phosphorescence under UV light. These reactions vary in colour depending on several factors, including the mineral's chemical composition, impurities, and structural characteristics. There are two main types of UV light reactions that you can observe in calcite-based minerals: fluorescence and phosphorescence.

Fluorescence occurs when a mineral absorbs UV light and re-emits it at a longer wavelength (visible light). This is a common reaction in calcite and other minerals. The fluorescence can produce a wide range of colours, from red to green to blue, depending on the presence of trace elements, radiation, or impurities.

Phosphorescence is a delayed emission of light that occurs after the UV light source has been removed. This is less common than fluorescence but can occur in some calcite-based minerals. When a mineral is exposed to UV light, electrons may become trapped in higher energy states and later return to their lower energy states, emitting light over time.

After my preliminary trip underground to Swildons Hole with my longwave and shortwave UV torches, I discovered that filtered longwave UV light generally produced a stronger reaction. I found that stalactites, stalagmites, and flowstone—typically made from calcium carbonate deposits—gave off fairly consistent reactions, fluorescing in shades ranging from bright white to pale blue. Many of these formations also phosphoresced in varying hues of green for about 1.5 seconds after switching off the UV torch. Unfortunately, it was quite late on a Friday evening, and as excited as I was to start photographing, I didn’t have the time or helpers necessary to do so.

Luckily, the following day, I had a Wessex Club trip booked to the Land of Hope and Glory in Wookey Hole, and I had high hopes for some fascinating UV reactions. Wookey Hole consists of a mixture of limestone and Triassic dolomitic conglomerate, with evidence of hydrothermal activity in the far reaches of the Land of Hope and Glory, where the large rift chamber was formed by hot, mineral-rich water. I had been told there were many interesting calcite formations, as well as some calcite crystals.

Land of hope and glory - Wookey hole - Somerset - UK

The final rift chamber, as hoped, didn’t disappoint. We found a range of different reactive calcite, but the star of the show was a stunning wall of dogtooth calcite, with hundreds of crystals, some as large as three inches in length! This particular wall fluoresced in a variety of colours but predominantly a beautiful ruby red.

Land of hope and glory - Wookey hole - Somerset - UK

Being mindful that I didn’t want to hijack the club trip and turn it into a full-blown photo shoot, I took just one photo to prove the concept and spent the rest of the trip scouting for other interesting minerals. The best method for capturing UV reactions turned out to be a mixture of single off-camera flash photography and light painting with the UV torch.

Buzzing with enthusiasm, I planned my next trip as soon as I could. All the images featured in this article were taken in the final rift chamber of the Land of Hope and Glory, where we were lucky enough to find fluorescent reactions in blue, white, yellow, red, and pink calcite.

Land of hope and glory - Wookey hole - Somerset - UK

The different coloured reactions under UV light in calcite-based minerals are caused by a combination of impurities, crystal structures, and defects that affect how the mineral absorbs and re-emits light. Factors such as trace elements and mineral inclusions also play a role in these colour variations. From my post-photoshoot research, I found that the colours are likely the result of specific minerals combining with calcite. For example:

• Red fluorescence could be due to manganese (Mn²⁺) ions, common in certain types of calcite or aragonite.

• Blue fluorescence may be caused by traces of copper or other transition metal elements.

• Yellow and orange suggest the presence of organic inclusions or certain trace elements.

• White calcite minerals may emit a white fluorescence due to the presence of other elements, such as calcium or trace impurities.

  
  

Considering the fascinating and diverse reactions we found in just one small section of a single cave, I can’t help but think the possibilities for UV light cave photography are endless, especially given the vast number of caves across the British Isles and their incredible geological diversity.

I’m currently working on "Adventures in Ultraviolet Light photography Pt 2," where I hope to share more of my findings from beneath the British Isles, including some fascinating phosphorescent reactions and even more amazing fluorescence from a variety of caves and mines.

A huge thanks to Duncan Price, Aga, Andy Rice, and Carl Barnes for their help with the photos and information about the cave.