If you’re thinking Keats needed to employ some pretty high-tech camera gear to pull this off, you’d be wrong. It actually is designed like the very first kind of camera invented, a pinhole camera, first created about 1,000 years ago. It consists of a thin sheet of 24-karat gold with a tiny hole punched in it at one end of a copper cylinder. At the back of the cylinder is a light-sensitive surface coated in thin layers of rose madder, an oil paint pigment.
The theory is that the small light exposure will slowly fade the pigment to different degrees based on the brightness of the objects in the image (mountains will fade slower than the sky, etc.). More permanent objects, like the landscape itself, will be clearer/sharper in the final image than things that moved or changed.
“Let's take a really dramatic case where all the housing is removed 500 years in the future,” Keats explained. “What will happen then is the mountains will be clear and sharp and opaque, and the housing will be ghostly. All change will be superimposed on one image that can be reconstructed layer by layer in terms of interpretation of the final image.” Assuming the camera, and someone to look at the image, survive that long.
