Hi-tech technique reveals hidden 'graffiti' on walls of Angkor Wat
Hi-tech photographic technique brings previously unnoticed paintings on walls of 900-year-old temple back to life 'like waving a magic wand'
Every year millions of tourists flock to Angkor, the magnificent temple complex which forms the spiritual heart of Cambodia.
Visitors marvel at the dizzying scale of the ruins and admire the intricately carved bas-relief friezes that adorn the walls - but there are numerous artistic creations that they fail to see.
Cutting-edge digital photographic techniques have recently revealed masses of paintings on the walls of the 900-year-old temple that are invisible to the naked eye. Despite extensive study by archaeologists over the years, many of them have never been noticed before.
Four years ago Noel Hidalgo Tan, a PhD candidate at the Australian National University and specialist in the rock art of Southeast Asia, made the startling discovery.
"In 2010 I'd just finished my master's degree and was spending three weeks working as a volunteer on excavations at Angkor Wat," Tan told the South China Morning Post.
"One day I was wandering around the temple during my lunch break when I noticed some smudges on a rock. I took photos of them because I thought there might be something there. When I looked at the images on my computer later, I was surprised to see some really quite elaborate paintings."
In 2012 Tan returned to Angkor Wat to conduct research for his doctorate. "I asked my Cambodian colleagues if they were aware of the paintings and they weren't. In some cases all you can see is a very faint trace of red colour, so it wasn't surprising.
"We surveyed all the walls, taking photos wherever there was a hint of pigment, and catalogued everything we found."
The results were published last month in a paper in the journal Antiquity.
Tan used a digital enhancement process called decorrelation stretch to examine the photographs. Originally developed for aerial and satellite mapping, the technique highlights differences in an image too subtle for the human eye to detect.
"It's like waving a magic wand" says Tan.
"The computer changes the colours on a pixel-by-pixel basis, so they move as far apart on the spectrum as possible. So if you had a light red and a dark red, it might turn one purple and one green. It allows us to view faint images with incredible clarity."
The team identified over 200 paintings dotted around the walls of the temple enclosures and were amazed at the variety and wealth of detail they found.
Boats are a common theme, with vessels ranging from small canoes to large flat-bottomed barges. Animals are also a popular subject, particularly elephants and horses, and there is one big cat, which might be a lion, and a curious reptilian beast with overlapping scales and multiple legs.
Other images portray deities and mythological figures, including apsaras - female spirits - and a simple line drawing of Hanuman the money god.
Illustrations of buildings include exterior views of Angkor Wat, and some pyramid-shaped structures which may represent Buddhist stupas.
Religious devotees have made pilgrimages to Angkor Wat throughout the ages and Tan believes some of these visitors felt inspired to express their piety by painting on the walls. "We think most of these paintings are instances of graffiti because they seem very random - they don't appear to have a system and many of them are quite crude in artistic terms."
However, one set of paintings is almost certainly not an act of vandalism. They embellish the walls of the Bakan, the sanctuary located in the uppermost tier of Angkor Wat and the most sacred space in the whole temple.
"All the other paintings are simple and were created independently of each other, but in the Bakan there are entire compositions" says Tan. "They're much more elaborate, they're painted with considerably more artistic skill, and they have a stylistic unity."
Bordered with pretty, diamond-shaped floral motifs, one scene depicts a Khmer pinpeat, a traditional musical ensemble.
Tan thinks the Bakan paintings could be relics of work undertaken to restore the temple.
"Angkor Wat was built in the 12th century, in what was then the capital of the Khmer Empire, and was originally a Hindu temple dedicated to the god Vishnu. Some time during the 14th or 15th century the capital was moved to Phnom Penh, the Angkor area was depopulated and the temple went into decline."
In the mid 16th century King Ang Chan moved the capital back to Angkor Wat and set about restoring it to its former glory.
"King Ang Chan converted the Bakan from a Hindu space to a Buddhist space. We think that the paintings belong to this period and were commissioned as part of the restoration work."
Tan hopes that other researchers will continue to investigate the paintings.
"There are other questions to answer, such as the meaning of the Bakan paintings and what they depict," he says. "And we don't yet know the age of the paintings. But if we can establish the composition of the pigments it might be possible to use carbon dating to find out."