Tribeca artist Robert Janz has been on a real tear—pun fully intended—with his recent “Witness Series (We’re What We Witness).” Using only water as an adhesive, he creates striking collages from the advertising posters you see everywhere: “I discovered that the commercial posters have so much glue on them that all I need to do is get everything wet. Pieces I cut out with my blade simply reglue themselves.” Janz’s work has long been about ephemerality, such as the mountain paintings that first drew my attention and the paintings in snow and water that disappear into oblivion, so he’s not surprised that the poster crews often cover the artworks up within hours. But collectors have been cutting them out and carrying them off—”which is why I say my collage is free, but my authenticating signature is expensive.” He has removed some himself, which is difficult because they tend to shred. The survivors are available for purchase at janzworkon.com, where SacSix, “a dedicated street artist who has taken up my cause and hopes to sell some rescued works to enthusiastic collectors.” You can certainly count me among them.