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17 Dec 2018

Photographing the unseen

Written by Christophe Brogliolo
The dining room at Kellie Castle
The Dining Room, Kellie Castle
Before getting started with Project Reveal in the Dining Room, we were told about some of the panels around the right window on the south wall. When we looked at them closely, we saw traces of original drawings that would have existed before the panels were repainted for renovation.
The right window on the south wall of the Dining Room, Kellie Castle
The right window on the south wall of the Dining Room, Kellie Castle

In the middle of the panels we could faintly see a lion on top of a crown, and a floral decoration in each corner. As we wanted to see these drawings more clearly, we tried using a specific photography technique that allowed us to see what’s behind the paint: infrared photography.

The panel on the middle of the left side of the window, showing a detail of the lion and a detail of the floral decoration.
The panel on the middle of the left side of the window, showing a detail of the lion and a detail of the floral decoration.

A digital camera is designed to record a little bit more than what our eyes can see. But when we’re talking about light, human vision is able to perceive just a small part of the whole electromagnetic spectrum. Human vision can see between 400 nm and 800 nm; digital cameras can catch anything between 350 nm and 1,000 nm.

The Light Spectrum (wavelength in nanometres [nm])
The Light Spectrum (wavelength in nanometres [nm])

At each end of the visible spectrum we have the ‘invisible’ spectrum of ultraviolet light and infrared light, which can be recorded using specific photography techniques. Ultraviolet light was mentioned by our colleagues from Project Reveal Team West in their article about Vaseline glassware.

This article concentrates on the infrared spectrum. Infrared photography is commonly used by conservators to study underlying drawings in paintings. When we see colours, the brain analyses the way that surrounding light is being reflected on the surface of an object. The object’s composition affects how it reflects light, creating what the human brain deciphers as colours.

A picture showing how the human eye sees colour in an object
By Flappiefh - Own work from this picture. The photograph is based on this work: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19885695

As infrared has a longer wavelength than visible light, it can reach different levels in various materials. Some materials that are opaque in visible light, such as paints and oils, become transparent under infrared light. Carbon black, graphite and coal drawings react particularly well to infrared photography as they absorb infrared radiation.

A drawing showing how an infrared camera sees colour in an object
By Flappiefh - Own work from this picture. The picture is based on this work: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19885695

A closer look at the other panels in the room revealed that two more have the same decorative traces. They’re located above the door to the Vigne Room. Having photographed each panel, we compared the results and noticed that each lion and crown is different. The curators intend to research why this is the case – maybe they were deliberately designed to be different, or maybe they were drawn by different artists. 

An image of four of the lions and crowns. The left picture is a standard photograph; the right picture is taken with an infrared camera.
An image of four of the lions and crowns. The left picture is a standard photograph; the right picture is taken with an infrared camera.

Below is an image from the very top panel to the right of the window, which shows some intriguing patterns at the top. We’re not sure of their significance or why they’re there. The infrared camera revealed that the pattern in fact covers the whole panel.

image_07_Montage03.gif?mtime=20181212133914#asset:159029

This specific photography technique is another example of how photographers can assist conservators, researchers and curators in their work to trace, document and show our collections’ wonderful history.


Project Reveal is a Trust-wide collections digitisation project. It will result in an updated database with high-quality images and unique object numbers for every item in the National Trust for Scotland material culture collections. Six regionally based project teams, supported by experienced project managers, will work across all our properties with collections to complete the inventory in 24 months from July 2017 until July 2019.

Project Reveal

Find out more about this Trust-wide collections digitisation project.

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