This script simulates a printing process from 1842:http://en.wikipedia.org/wiki/Cyanotype
Copy it into the scripts folder from GIMP, you will find it then under Filters -> Artistic -> Cyanotype.
If you like it, hug someone.
An example can be found here:http://www.flickr.com/photos/28653536@N07/4435497335
Unless otherwise noted, the rights for the individual plugins are with their respective authors. Logo image by Jakub Steiner.