Sunprinting, also called cyanotype or “blueprinting,” is the oldest non-silver photographic printing process. The paper is coated with light-sensitive chemicals, which react to light waves and particles when exposed to sunlight. When you place objects on the paper, they block the light (paper remains white), while the areas on the paper around them turn a beautiful Prussian blue (ferric ferrocyanide). Water stops the process and fixes your images on the paper.