Restoring Ancient Artifacts With Frickin’ Laser Beams

Few technologies evoke the future like lasers. For instance, who can forget the opening sequence of Star Wars?

The awesome yellow planet of Tatooine emerges from a total eclipse, her two moons glowing against the darkness. A tiny silver spacecraft, a Rebel Blockade Runner firing lasers from the back of the ship, races through space. It is pursed by a giant Imperial Stardestroyer. Hundreds of deadly laserbolts streak from the Imperial Stardestroyer, causing the main solar fin of the Rebel craft to disintegrate.
Star Wars Episode IV – A New Hope,  George Lucas 1976

Woohoo, lasers! Pew pew pew pew pew! Ahem.

While we don’t have deep space firefights just yet, we have figured out how to harness laser technology in a variety of interesting ways – such as restoring art by using lasers in carefully controlled bursts.

For those of you unfamiliar with how lasers work, here’s a basic rundown:

The visible light spectrum is made up of light in a certain range of wavelengths. Light whose wavelength falls outside this range (such as infrared and ultraviolet) is not visible to the human eye. Different wavelengths of light all carry different amounts of energy: the longer the wavelength, the lower the energy. High-energy light like ultraviolet can be very dangerous–it is what causes sunburns and skin cancer. Just as it is damaging to human skin, it is also damaging to artwork, so it makes sense that engineers do not want to expose art to high-energy light. This is where lasers come in.

A normal light source, like a light bulb, emits a spectrum of different wavelengths of light (including high-energy) in all directions. A laser, by comparison, emits only light of a single wavelength and does so in a tightly focused beam. Because engineers can choose what wavelength of light is emitted, the laser becomes a very powerful and precise tool, as it allows the choice of a single wavelength that will not damage the art.
– The Beauty of Science:  New Technologies in Art Restoration

Essentially, a specific wavelength of light is focused into a tight beam. Because there is only a single wavelength, this beam has very specific properties that allow it to be carefully controlled. Now the fun part. Lasers are being used instead of more traditional methods of surface restoration involving harsh chemicals like solvents that often lead to over-cleaning, damaging the original artwork, or interact with the chemical structure of the pigments, leading to discolouration or instability. With lasers, engineers can carefully calculate the depth of the soot, dirt, and old varnish they want to clean off and zap it into nothingness. This process is called laser ablation.

Engineers choose a low-energy (large) wavelength that will interact strongly with the dirt and varnish, but not as much with the surface of the art itself. This is usually a wavelength of about 1065 nanometers, which is in the infrared range of the light spectrum [2]. Using a laser, they then fire short pulses of this light at a point on the surface of the artwork. The majority of the light energy is transferred to the dirt or varnish, heating it to such a degree that it literally jumps off the surface. This expulsion of materials is called ablation.
– The Beauty of Science:  New Technologies in Art Restoration

“But wait”, you say, “How do they know exactly how deep to go?”

This is basically the reason laser ablation wasn’t used much in the past, for fear of damaging the artworks being restored. Engineers figured out a solution, though:

Laser Induced Breakdown Spectroscopy (LIBS) is a method of examining the composition of the material being ejected from the artwork. When particles are ejected from the surface of the artwork, they give off an energy pattern specific to the material of the particle. Varnish, for instance, gives off a different energy pattern than paint. When the LIBS detects a shift in the energy pattern signaling that paint is being ejected (meaning the light has penetrated too deeply), the laser shuts off to avoid further damage [3]. Because the process is automated and done in real-time, it can be used to control the laser pulses, totally eliminating the need for human guesswork and thus safeguarding the artwork.
– The Beauty of Science:  New Technologies in Art Restoration

With this awesome, futuristic-sounding technology, an incredible amount of restoration is now possible. Take, for example, the restoration of the Villa of Mysteries in Pompeii.

Conservators are using lasers to clean the delicate frescos in one of Pompeii’s most popular sites, the Villa of Mysteries. If successful, it could change the way future conservation projects are carried out there.

The Villa of Mysteries, first excavated in 1909, is named after a large and colourful cycle of frescoes showing young women undergoing an ancient Roman marriage initiation rite. Conservators are using laser technology to restore the colours to their former glory. Pompeii officials released a statement saying this is the first time the technique has been applied to such an important cycle of works a the site and that “it constitutes a viable alternative for preserving surfaces that might be too sensitive for [traditional] mechanical and chemical methods of conservation”. The laser is able to detect and remove the different protective layers that have been applied to the frescos by previous restorers.
– Great Pompeii Project Finally Underway

The results are pretty spectacular, to say the least – check out this before-and after of one of the frescoes:

Laser cleaning is being used on larger scale projects, too, like the restoration of Diocletian’s Palace in Croatia:

Conservators in Croatia have completed a ten-year project to remove more than 1,700 years of grime from the courtyard of the palace of the Roman Emperor Diocletian (AD244-311), in the coastal city of Split. Lasers were used as the primary method to clean the peristyle of the fourth-century imperial residence—an innovative technique that is normally reserved for cleaning individual sculptures or details of larger architectural elements, as opposed to whole structures. According to the architect Goran Niksic, who works for the city, this is the first time lasers have been used on this scale in Croatia to clean stone.

The peristyle was covered not only in soot, but also in cement dust from a nearby plant that was active in the late 19th and the first half of the 20th centuries. In some parts, the build-up of grime was up to a centimetre thick.
– Diocletian’s Palace Gets Laser Facelift

Yes, they are using frickin’ laser beams to restore an entire palace.

Diocletian’s Palace before restoration

Not too shabby, right? But check this out:

Diocletian’s Palace after restoration

It’s like a time machine. Powered by frickin’ lasers.