Sun printing paper PhänoMINT

Printing on paper using only the sun? With the special sun printing paper, the most amazing prints can be created. Simply place various objects like leaves, flowers, or puzzle pieces on the paper. It is then placed in the sun for a while and afterwards put in a water bath. It immediately changes color and the print becomes visible. But how is it possible to print using only sunlight? The paper is coated on the darker side with iron-containing powder. The sunlight reacts with it to form a blue dye.