On a camping trip with our new Cub Scout troop and their families, one of the projects that was done while we were there was to meet Elective 12a, making solar prints as part of the Nature Crafts Elective that we were trying to fulfill while on this camping trip.
The Cub Scouts all picked out their respective leaves, placed them on the black construction paper provided and placed one or two rocks on the leaf, before leaving it in a sunny spot to make the print.
My son's leaf solar print did not show up, (as shown in the last photo) and this was not acceptable to me - the crazy-Engineering-craft-loving mom who likes to see things through and to see them work.
We were given additional sheets of black construction paper to perform the experiment/craft at home, and one weekend of sunlight, we did just that.
I titled this Instructable "DIY Construction Paper Solar Prints" because I looked for online tutorials about performing solar prints, only to be disappointed in finding people purchased a special kind of solar paper to do their prints. Although those prints come out really cool with the color changing paper, we used the materials we had on hand (hence the less expensive route) and I was happy that all three of my children (ages 3, 4 and 8) were interested in the project and were able to do it.
As stated in the intro, my children and I did this project to meet a Cub Scout Requirement, specifically, Bear Elective 12, Nature Crafts. As part of that requirement, the Cub Scout is to make solar prints of three kinds of leaves (part a.) The Cub Scouts in the Bear Group are usually eight to nine (8 - 9) years old.
Depending on your use of this project, you could include a small discussion of what ultraviolet (UV) radiation is to enlighten the children. This is not a requirement for meeting the Elective, but it's good to get in a teachable moment with my 8-year old where I can.
For the purposes of this experiment/craft, what is occurring is that the UV rays of the sunlight are discoloring the black construction paper by a chemical reaction.
The black dye in the construction paper is breaking down in the sunlight, due to the ultraviolet radiation. The portion of the construction paper that is covered by the leaf (or leaves) is blocking the sun from breaking down the color in the construction paper.
While talking about it with my children, I compared this to getting a suntan. I described how the color on the paper was changing just like skin changes when you've been in the sun for a while. The skin under clothes doesn't normally get changed and stays the same color, just like the color of the paper under the leaf. Of course with the skin, it turns darker (or red) whereas the paper got lighter under the sun, but it still changed.
I found articles and great photos by NASA on various websites that can be used to talk about the sun and the effects of UV rays. The discussion could be done in greater detail depending on the age of the children and what the purpose is for.
Notes about the sun in general: Solar and Heliospheric Observatory site
An excellent description of the parts of the sun: How the Sun Works by How Stuff Works
A description of the different type of UV rays: Ultraviolet Radiation by Health Physics Society
A description of what type of UV rays are harmful to our skin: Stay Safe in the Summer Sun by the FDA*
*Note: There is a 2-minute video on this site that describes how the UV rays affect your skin and what sunscreen does for it.