Our post yesterday regarding infra-red film from Maco lead me on to look and see which of the infra-red filters are in stock.
Looks like we have a fresh supply of Kenko IR filters in 49mm, 52mm, 67mm, 72mm, and 77mm size. They are dark as and prevent ordinary light from penetrating to film or sensor - only the IR gets through.
The results can be charming, with white foliage and black skies on monochrome or wild colours with a colour setting on a digital camera. Exposure is long, and you need to let the camera decide this for itself sometimes - you can't focus by normal means either - you have to set the distance scale yourself and it has a slight offset for the IR wavelengths.
Serious experimenters would do well to get a book from the library about this, or search out one of the Fawcett publications from the bookstore. Like pinhole photography, IR imaging is a totally scientific and absolutely predictable fairy tale told in a foreign language in the dark in a high wind so be prepared for anything...