Sun printing is a process which will fascinate children. Using light-sensitive paper (often called "sunprint paper" or "cyanotype paper") it is easy to make beautiful white-on-blue prints of flat natural objects such as leaves, flowers or feathers. The images will appear "magically" in just a few minutes on a sunny day, and the resulting images can be displayed as artworks or used for a variety of craft activities.
You will need to invest a little money in this, although a cheaper version which does not use photo-sensitive paper is mentioned below. The basic idea is to collect some interesting natural objects, arrange them on a sheet of the sunprint paper, expose them to sunlight for a few minutes (or to a cloudy sky for longer) and then to wash off the chemicals and leave them to dry. The process is described in detail at this web site, which also explains what is happening. The prints will be much sharper if the natural items are held down flat against the paper during exposure to the sun, so it is worth placing a sheet of perspex or glass on top. You might want to invest in one of the "Sunprint kits" supplied by the Lawrence Hall of Science, which includes a perspex sheet. You can easily find these for sale online, for example from Amazon.
Not only will this activity highlight the delicate and varied form of leaves, flowers, seed heads and feathers, but it may also interest older children in chemistry. The ultraviolet rays included in sunlight are reacting with a chemical in the paper. Initially this bleaches the blue colour of the photosensitive paper, but when washed in water a second chemical reaction takes place which turns the exposed areas blue, whilst the chemicals in the unexposed areas, which were protected from the sun by your natural objects, are washed away by the water, leaving white paper behind.
The pictures produced can be displayed as they are, or framed, but they can also be used to make attractive book covers, or to cover small boxes used to store "treasures" or to contain presents. If you want to do this, then take care to buy sufficiently large sheets of sunprint paper. Some of those available for sale are quite small.
If the cost of photosensitive paper (typically £1-2 each for an 8x10 inch or A4 sheet) deters you, then there is a much cheaper approach using coloured sugar paper, which simply relies on the fact that the colour in the paper will fade in sunlight. This takes a good deal longer (e.g. a day or more in full sun) and will not produce images with the same level of clarity, but it is a lot cheaper. You can find a guide to this approach from the Natural History Museum here.
