When you walk into a museum you're likely not thinking about chemistry. Yet you probably ought to be. Before the industrial revolution brought us manufactured pigment, painters had to be great chemists—tinkering with rare, expensive, and sometimes downright poisonous chemicals to make colors.

At London's National Gallery this summer, a show called Making Colour looks at this lost era of art and science, taking visitors through a succession of galleries devoted to specific colors and how they were made. The show is as much about discovering these ingredients as it is the paintings—for example, in one video, a conservator shows us how a tiny fleck of purple paint is cast in a resin block and then ground down to study under the microscope. What's revealed? A microscopic mixture of red and blue, of course:

We've looked at this topic before—last year, Hyperallergic did an awesome post about obsolete pigments that included colors like Indian Yellow, a paint made from the urine of cows forced to only eat mangoes. But Making Colour gives us a bit more context. Below, find several interesting ingredients mentioned in the exhibit—along with a few extras of our own.

Orange: Arsenic

Orange pigment was tricky—according to the National Museum, it was notoriously difficult to come by. One method included using realgar, a mineral that's also known as "ruby of arsenic." Extremely poisonous stuff, it was used as rat poison and weed killer throughout medieval Europe—it also serves as the base for this 1685 painting by Rachel Ruysch.

Image: The National Gallery, London.

Green: Copper Patina

The green background of Hans Memling's 1475 painting, The Virgin and Child with Saint John, was made by mixing oil with verdigris—another name for the poisonous pigment that's made from the patina on aging copper, the same stuff the Statue of Liberty is coated in.

Image: The National Gallery, London.

Red: Insect Bodies

In the museum's "red room," curators describe the various ways in which painters achieved deep ruby reds—like carmine, which is made by boiling down crushed bodies of insects that naturally produce carminic acid. The red gown in Albrecht Durer's The Virgin and Child, for example, was produced with variations on carmine red, according to Pigments Through the Ages. Carmine is still used commonly in consumer products—and food.

Image: The National Gallery, London.

Blue: Gemstones

From azure to lapis lazuli, the creation of pure blue was an expensive affair. This 1691 Pierre Mignard painting, The Marquise de Seignelay and Two of her Sons, has crushed up lapis lazuli to thank for its deep cobalt color.

Image: The National Gallery, London.

Black and Brown: Human Remains

Though black doesn't feature heavily in the exhibit, it's worth mentioning that for hundreds of years, painters used charred animal bones to create a dark matte black called Bone Black (in fact a company called Ebonex still makes it). Likewise, Mummy Brown was made from the ground-up skin of excavated Egyptian mummies (and sometimes mummified cats!). It became popular in the 19th century, when it was used to create deep, warm browns like those in this 1814 painting by Martin Drolling.

There are plenty of other now-forgotten hues out there, so drop them in the comments below. If you're in London, Making Colour closes on September 7.