Will Ashford's "Look for Art" and "Experience 261." Ashford explains his methodology on his website:

1. The words are revealed through application of translucent colored vellums.
   
2. Using pencil and ink new images are at times added or subtracted from the page.
   
3. Sometimes I build new words out of the parts of other words. For example: I have a strong attraction to art about art and often choose to make art about the word “art”. I find “art” just about everywhere.
   
4. And, as you might expect, there are countless variations.
   

More here and here.