Pier Roberto's contrast is the one between B&W and colors
Along with his contrast card and two bank notes, Pier Roberto sends two calls (cf. his websites http://stamp-dater-art.blogspot.it and http://fromzerotoinfinito.blogspot.it)
Roland writes: "The contrast depends on you - how you will document it".
At first, seeing the card, I noticed a contrast between the SILVER and the BLACK, and between the IMAGE IN THE MIRROR (on the card :) ) and the IMAGE I HAVE OF MYSELF (but that I also know from mirrors -and photos). Making a photo of the card, I now see a contrast between the RIGHT SIDE - and the LEFT SIDE OF THE SILVER IMAGE.