Over the years since photography was invented in 1839, the generally accepted date of "practical photography, photographer have used any number of materials to fix an image from salt paper printing to modern day pixels. Many of these experiments have proven to be exceptionally challenging to preserve. Lachlan McLean, for example, dragged these 22"x18" mammoth glass plates around Georgetown and Idaho Springs to obtain immediate large-scale exposures.
During the digitization process, many have had to be puzzled back together after experiencing numerous cracks, breaks, and wear. The positive image is of the train on Georgetown Loop trestle near the turn of the century.