Capillary Action Sun Prints

Until digital cameras came along, most people took photographs on film and printed them out on paper. But one of the first types of photograph, known as sun prints, lets you make an image directly on paper—no film or camera needed! Early photographers like the British scientist Anna Atkins made sun prints to record plant specimens. Atkins took ferns, leaves, and flowers, lay them on the paper, and put them out in the sun. Special chemicals in the paper turned dark wherever the energy of the sun hit them. Areas that were covered stayed light. Artists still make sun prints—or to use the fancy name, heliographic art—to create special effects on paper or fabric. 

A sun print is a type of negative image because the light and dark areas are reversed. Film cameras also produce negatives. When you press the button, the shutter opens and lets light in. Wherever the light hits the film, the film turns dark. To make a print, you have to reverse the process by shining light through the negative onto light-sensitive paper. In the final product, the light and dark areas are back to normal. 

A true sun print is sometimes called a cyanotype, because the special ink used turns the paper or fabric cyan, a type of blue. But you can get the look of a sun print by covering a piece of fabric with ordinary acrylic paint—and make it any color you like! In this version, the paint doesn’t go through a chemical change. Instead, the wet paint is wicked away from areas that are wetter to areas that are drier. The sun dries the parts of the fabric that are uncovered faster than the parts that are covered. This leaves a lighter “shadow” behind that is shaped like the object you placed on the fabric, just like in a real sun print. 

The wet paint moves because of capillary action, the ability of water to move inside materials containing a network of small openings. (A capillary is a very narrow tube.) It’s the same thing that happens when you use a towel to wipe up a puddle of water on the kitchen counter. All substances, including water, are made up of tiny molecules. Molecules are the smallest part of a substance that still acts like that substance. Water molecules tend to stick together, which is why water forms drops and puddles with smooth rounded edges. Water molecules are also attracted to some other materials, like cotton cloth. When you blot a puddle with a cloth, the pull of the cotton is stronger than the force holding the water molecules together. The water gets pulled into the spaces between the threads in the cloth. These openings act like little straws that suck the water in. If the cloth is damp, it can pick up water even faster, because the water in the cloth also pulls on the water in the puddle. 

Try making a Capillary Action Sun Print and see what kind of effects you can create!