Dawnsilver

The majority of lodes and veins throughout Cervus mountain are mundane silver of a pure quality, but they are speckled in places with small quantities of the Dawnsilver, an exceptionally lightweight and precious material.
  When polished to a mirror finish, Dawnsilver "catches" images; the reflections stain the mirror with their image, leaving an imprint of everthing that has ever been reflected in it. This property is exploited to create rudimentary visual records; two playing-card sized pieced of Dawnsilver are affixed together inwards, connected with a spring hinge and held shut with a latch. When the latch is triggered the mirror snaps open and captures the image in front of it. It is closed and relatched to prevent the image from being unintellegible, as each time the camera is opened to view the image it becomes muddled with more noise as the mirror picks up the images of wherever its being viewed. This makes permanent records unviable with Dawnsilver and limits its use as evidence in court cases. The items are typically only one-time use, and as they have to be made entirely in a dark room to prevent contamination of images during manufacture, they are pricey as well, further limiting their application. Many people view the technology as a novelty due to its limitations.