I had heard of platinum prints before, but I wasn’t really sure what made them unique. So I asked Heather Shannon, a photo archivist at the National Museum of the American Indian (NMAI), to explain their significance. Here’s what I learned:

Invented in the 1870s, platinum is a way of making photographic prints that have a few standout qualities—wide tonal range that creates deep blacks, creamy whites, and every shade of gray in between; a diffused look that comes from the way the image is embedded in the fibers of the actual paper; and most importantly, at least for the purposes of this post, platinum prints are lasting. They are, to use the word chosen for the title of an