recipies: invsible ink

http://inthetrenchesofmotherhood.com/?p=99
This is a really simple one.
Squeeze some lemons or limes into a glass. This juice will be the ink.
Give them a small paintbrush or a Q-tip to use as writing implement.
Have them write the message on a sheet of white paper. When the “ink” dries it will be invisible.
To make the message reappear, hold the sheet of paper over a heat source. A hot water bottle, heating pad, in front of your wood burning stove, a heat register are some ideas.