ArtLex
Art Lex: Impasto
This page contains a brief definition for "impasto" and provides some examples of paintings made with impasto technique.
ArtLex
Art Lex: Frottage
This page contains a definition for "frottage." Read about what it is, when it was first introduced, and view an example of a piece of art that uses the frottage technique.
Other
Mesoweb: Rubbings of Maya Sculpture
This site is a personal account of an artist's trip to do Mayan rubbings. Includes images of the rubbings.
Wikimedia
Wikipedia: Impasto
Wikipedia offers a basic definition for what impasto is. Also lists the types of paintings it is primarily found in and the painters it is commonly associated with.
Other
Alfred Currier
This site offers images of paintings done by a contemporary artist using the impasto technique.