Stamp box directory
AZO stamp box: dates and marks
AZO was Kodak's workhorse photographic paper, and it is by far the most common back you'll find on real photo postcards — which is why its corner marks matter so much: the marks changed over time, and each pattern carries its own date range.
Four triangles pointing up
1904-1918
Diamonds in corners
1907-1909
Two triangles up, two down
1918-1930
Nothing in corners
1922-1926
Squares in corners
circa 1924–1949
Ranges cross-checked across: the2Buds.com chart, as republished by Sports Collectors Daily, 'Dating Vintage Real Photo Postcards'; SABR Baseball Cards Research Committee, 'Dating and Authenticating Real Photo Postcards' (2017); Postcards Everywhere collector chart (2010); Postal & Paper, 'Dating Postcards by the Stamp Box' (2026); Playle's Directory of Stamp Boxes (playle.com, frozen reference; marketplace closed 2020); Playle's detailed stamp-box directory pages (playle.com/realphoto/photoa.php, photod.php; image-keyed, contributor-verified; fetched 2026-07-18). Approximate by nature — see methodology.