Félix Nadar

These paper samples are examples of carbon tissue, the main material used in the process of carbon printing. Carbon tissue is a sheet of paper coated with a mixture of gelatin, pigment, and light-sensitive material. When this sheet is placed under a photographic negative and exposed to light, the gelatin mixture hardens and becomes insoluble wherever the light falls. The hardened gelatin is then transferred to a new sheet of paper and the remaining gelatin washed away, leaving behind the final image. 

The word carbon, in this case, refers to the pigment carbon black, but any color of pigment could be used.  For this reason, carbon prints became a popular way to reproduce drawings made using historical materials, such as red chalk or blue-toned paper.