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Artists create all sorts of paintings, sculptures, and architecture that help make our world beautiful and capture moments in history. But without scientists, we would’ve lost most of this art by now.

Art gets dirty and damaged over time. And if you try to clean it without paying attention to chemistry, you could do more harm than good. Thankfully, scientists have been learning how to restore artwork in some pretty cool ways that are effective and safe.

And a little weird, to be honest. One way of cleaning 3-D artwork — like, sculptures or architecture — is by blasting it with a laser. Which sounds counterintuitive... but awesome.

This method is called laser ablation, and it was first developed in the 1970s to get something called black crust off marble. This crust is a combination of pollution from the environment and the mineral gypsum — which can form if marble is exposed to acid rain. And it can be hard to get off.

Using chemicals or scraping it isn’t always precise and can damage the art underneath. Laser ablation gets around those problems by using short pulses from a handheld laser to dislodge grime. To make sure conservators don’t accidentally melt any statues, the length of the pulse is carefully controlled by a computer, and it usually only lasts a few millionths or even billionths of a second.

The lasers also use infrared light, since that has a longer wavelengths and carries less potentially-damaging energy than visible light. Once the laser is turned on, the light heats up and expands the black crust. That expansion creates waves of pressure that ultimately detach the grime — all without affecting the marble underneath.

It’s actually a little like how tattoo removal works — except those lasers are breaking up the ink in your cells into smaller pieces, not blasting it off your body. Lasers might seem like the gold standard for cool science. But to repair some paintings, scientists got even more creative:.

They trained dirt-eating bacteria. A few years ago, art conservators in Italy were working to repair a series of 400-year-old frescoes — a kind of painting done on wet plaster. After decades of pigeon poop and harmful restoration attempts, the frescoes were in pretty bad shape.

They were covered in waste, salt, and glues from those older, botched restorations. And to make things even worse, the chemicals that conservators were using to try and clean them were actually damaging the paint. That’s where bacteria came in.

By working with microbiologists, the conservators identified a strain of bacteria that could actually eat the salts and glues right off the paintings. In only a few hours, it removed 80% of the damage without touching the pigments underneath. It’s called Pseudomonas stutzeri, and it’s pretty common in dirt and water.

These bacteria can get energy from all kinds of compounds, and they’ll actually produce different proteins depending on the food source they’re given. So by growing them in specific mixtures of old glues and salts, biologists can actually “train” the bacteria to make proteins that eat away the grime on frescoes. As long as they don’t include pigments in the training mix, the bacteria won’t touch the original artwork, either.

After a few hours with these organisms, the paintings looked practically as good as new. Or at least, way better than they did. Bacteria has since been used to clean more paintings, some up to 700 years old.

And besides helping us, they’re getting a free meal out of it — so it’s a win-win. Now, possibly the most satisfying method of art restoration is cleaning off yellowed varnish with some careful chemistry. For real, you can watch all kinds of videos of this online.

Varnish is applied to oil or acrylic paintings for a few reasons, including to protect the art from dirt. Formulas can vary, but it’s generally made of a drying oil, a resin, and some sort of thinner. The resin is a sticky substance — like pine resin — and it forms a hard coating on the painting after everything dries.

The problem is, resins often change color over time. After years of exposure to light or oxygen, compounds in them break down and turn yellow or even brown. And it’s not pretty.

Taking off the old varnish is a challenge, because the chemicals used to do it can just as easily erode the paint underneath. So art conservators have to become chemists. First, they’ll slowly wipe away the old varnish using a chemical like acetone, a carbon-based molecule that’s great at dissolving resin.

Then, they also have to remove the acetone residue, so it doesn’t keep dissolving the original paint. To do that, they’ll use a neutralizer. These are often mixes of chemicals — like oils — that stop a varnish remover from reacting, or from being so acidic or basic.

The exact chemical they’ll use will depend on the remover itself. For example, with acetone, they can use a mix of petroleum and wintergreen oil. Then, once everything is clean, the painting is ready to be re-varnished or put back on display.

Without science, conservators could accidentally turn a work of art into, well, kind of a mess. But thanks to techniques like these, they can keep preserving beautiful pieces of art — and history — so we can enjoy them for decades to come. Thanks for watching this episode of SciShow!

Besides restoring art, scientists are also pretty talented at busting art forgeries. If you’d like to learn how, you can watch our episode all about it. [♪OUTRO].