Riepenhoff got the idea three years ago while studying cyanotypes, an old photo technique that involves placing objects on paper coated with iron and potassium ferrocyanide. When exposed to light, the paper turns a brilliant blue. She became obsessed with Anna Atkins, who made cyanotypes of seaweed in the 1840s. Tired of working the darkroom, Riepenhoff carried a few sheets of cyanotype paper to the beach near her Sausalito studio, curious to see the water’s effects. The results were stunning—conjuring the sand and waves on the paper.