Several of Renoir's portrait paintings have a soft, pastel background with mottled colors. It's always reminded me of something you'd see as a backdrop in a senior class photo, circa 1979. But the paintings weren't always this way. Renoir, like many other Impressionists, loved the color crimson lake, or cochineal. In an age that pre-dated synthetic oils, this brilliant red color was achieved with extracts from the bodies of certain insects. Unfortunately, it also fades rather quickly.

Researchers in Chicago have produced a visualization of how they think a Renoir could have looked before its colors faded.

How much of the way we see art today is a product of time? In a similar vein, one of Rembrandt's most famous paintings, The Night Watch, is actually titled The Shooting Company of Frans Banning Cocq.It was not a night scene at all, but a group heading out in broad daylight. Rembrandt used a heavy varnish that yellowed and darkened with age, which eventually gave the (mis)impression that the painting was of a night scene, and which gave the painting a new name, as well.

When the Sistine Chapel was first revealed after a decades-long restoration, many people were outraged. Instead of the soft, muted, almost sepia-toned images they knew as Michelangelo's art, the ceiling was covered with stunningly bold, bright colors. That was, in fact, Michelangelo's style, there was just no one alive who knew it prior to the restoration. The softening and browning of the colors had been a gradual process, a slow, steady deposit of candle wax, incense smoke, pollution and body oils over hundreds of years. All the restorers had done was clean the surface of the ceiling, to reveal the unfiltered colors beneath.