The person who took these pictures was a spectacular photographer!
Mathieu Stern, a French photographer and filmmaker living in Paris, learned of a possible time capsule in his old family home. Upon finding a box dating from around 1900, he noticed glass plate negatives inside and decided to develop them using an old photographic printing process called cyanotype.
The cyanotype process produces a cyan-blue print and is commonly associated with engineers’ blueprints. It was popular in the early 20th century as a simple and inexpensive way to produce copies of drawings.
