Sun Print paper is activated by the sun's rays. Objects from nature or man made that are placed on the paper create positive and negative space. Objects that are put on top of the paper block the rays from passing through that area of the paper. These objects create a positive space. The areas left open on the paper are where the sun's rays activate the paper and become the negative space.
I begin by telling my students that Sun Print Paper is light sensitive and the sun's rays activate the paper. I show students samples of finished Sun Prints so they can be inspired by the variety of objects you can use and how they can be arranged on the paper. It also gives them an idea of the range of blues and whites that can be achieved. Before you give your students a piece of Sun Print paper make sure they have their objects and a design in mind. Students need to work quickly placing their objects on the paper once it is exposed to the sun. I find that the sun is so strong that exposing the paper to sunlight for a minute is usually sufficient. Or, you know its time to remove the paper from the sun when you watch it go from a medium blue to a pale blue. Once the paper has been exposed to the sunlight it needs to be put into a cool water bath for a minute. The water stops the activation process and reverses the colors (initially the positive space is dark blue and the negative space is pale blue). After a minute take the Sun Prints out of the water and hang them up to dry. I notice that after the water bath the colors continue to lighten and darken.
If your Sun Print looks washed out and there is no definition between your object and the paper it has probably been over exposed to the sun. Next time make sure you watch the paper and the time. Don't let the paper go past the pale blue stage.