La Brea

“To create images of the fossilized remains of the animals trapped in the Los Angeles tar pits, Brandt used a photographic process known as heliography. First, he created negatives from fossils housed at the tar pit's museum. Next, Brandt collected actual tar from the site, spread it across an aluminum plate, placed the negative on top, and left it to bake in the sun. The tar that was exposed to the light solidified to the aluminum so that after he washed it, the fossil "print" revealed itself.”

—The Week, The surprising beauty of tar and dust, by Loren Tablot

https://theweek.com/captured/447989/surprising-beauty-tar-dust

“Brandt has revived the oldest photographic technique, the heliography process devised by Niépce in 1826 to make that view from the farmhouse window regarded as the oldest surviving photograph. This technique was not silver-based but used tar, bitumen of Judea, as the light-sensitive medium.

The La Brea tar pits in Los Angeles is a natural formation of underground tar welling up to form a small lake, it’s black and bubbles with gas as you watch it. Prehistoric bones were found preserved in it and are mounted in a nearby museum. Brandt photographed these displays of sabre-tooth tigers and the like, and made large transparencies – very large. Then he collected tar from the tar pits, coated large sheets of aluminium, laid the transparencies over them and left them in the L.A. sun. It’s not stated how long Brandt left them to bake, but Niépce took eight hours. After washing them to remove the soft tar, only the sun-hardened parts remain, “leaving an image of the fossil created from its ancient remains”.”

—Matthew Brandt’s Tar by Greg Neville

https://greg-neville.com/2014/05/21/matthew-brandts-tar/