Many of the most famous oil paintings ever committed to canvas, like Leonardo da Vinci’s Mona Lisa and Rembrandt van Rijn's The Night Watch, aren't just made of paint, but include a top layer of protective varnish, too. This clear coating preserves the paint beneath it for centuries, but it also decays and darkens over time, causing scenes to look vastly different than what the artist intended. To demonstrate how much aged varnish can affect a painting, art dealer Philip Mould (co-creator of the BBC One show Fake Or Fortune?) recently gave his Twitter followers a step-by-step look at the restoration process.

As Mashable reports, the varnish on the 17th-century painting in the clips and photos below is 200 years old. Painted in 1618, the image depicts an anonymous Jacobean-era woman who posed for the portrait when she was 36.

As the varnish is stripped away from the piece with a paintbrush and solvent, you can see the soft, rosy colors the artist originally chose start to come through. The process reveals colors and details that would have been lost as long as the yellowed protective layer remained.

For a closer look at how professionals can salvage paintings from the destructive forces of time, check out these behind-the-scenes secrets of art restorers.

[h/t Mashable]