microfiche vs rubbings

microfiche

noun
  • A sheet of microfilm, six by four inches, holding several hundred reduced images of document pages, read using a microfiche reader or microfilm reader. 

  • A device used to magnify and read these sheets. 

verb
  • To convert (documents) to microfiche format. 

rubbings

How often have the words microfiche and rubbings occurred in a corpus of books? (source: Google Ngram Viewer )