We tend to imagine old paintings as having a muted, yellow-brown cast, and not without reason. Many of the examples we’ve seen in life really do look that way, though usually not because the artist intended it. As Julian Baumgartner of Chicago’s Baumgartner Fine Art Restoration explains in the video above, these paintings’ colors have changed over the decades, or in any case appeared to change, because of the layer of resin on top of them. When that kind of coating is first applied, it actually makes the hues underneath look richer. As time passes, alas, chemical changes and the accumulation of dirt and grime can result in a dull, even sickly appearance.“A lot of people say that the varnish should never be removed, “that that’s a patina that is on the surface of the painting and that it adds to the painting’s quality: it makes the painting look better, it makes it look more serious,” says Baumgartner.“Those are all interesting opinions, but they’re all inaccurate. If the artist wanted to apply a patina to their painting, they could apply a patina and tone down the colors. But most artists, when they apply a varnish, do not envision that that varnish will ever become yellow or brown, or will crack or become cloudy.” The idea is to get the colors back to how the artist would have seen them when the work first attained its finished state.Therein lies the difference between a painting and, say, a cast-iron skillet. But on some level, the actual labor of cleaning a work of art — as Baumgartner demonstrates, sped-up, in the video — differs less than one might imagine from that of cleaning a kitchen implement. The result, however, can certainly be more striking, especially with a canvas like this one, whose twin-sister subjects provide an ideal means of showing the contrast between colors long covered by varnish and those same colors newly exhumed. Though there now exist formulas that don’t turn yellow in quite the same way, more than a few artists stick to the classic damar varnish, which does have advantages of its own — not least keeping a few more generations of conservators in business.Related content:How an Art Conservator Completely Restores a Damaged Painting: A Short, Meditative DocumentaryA Determined Art Conservator Restores a Painting of the Doomed Party Girl Isabella de’ Medici: See the Before and AfterWatch an Art Conservator Bring Classic Paintings Back to Life in Intriguingly Narrated VideosThe Art of Restoring a 400-Year-Old Painting: A Five-Minute PrimerWatch the Tate Modern Restore Mark Rothko’s Vandalized Painting, Black on Maroon: 18 Months of Work Condensed Into 17 MinutesThe Joy of Watching Old, Damaged Things Get Restored: Why the World is Captivated by Restoration VideosBased in Seoul, Colin Marshall writes and broadcasts on cities, language, and culture. His projects include the Substack newsletter Books on Cities and the book The Stateless City: a Walk through 21st-Century Los Angeles. Follow him on the social network formerly known as Twitter at @colinmarshall.