Dating kodak photo paper
In printed images the grey areas are usually made up of black marks that are spaced to create the optical illusion of greys.
Though most of us today are familiar with the concept of photo grain, this is mostly because we have experienced very large prints made from small 35mm negatives.
Observing this shiny crust, no mater what the color, is a quick and sure way of telling if you are looking at a real photo.
A common problem with real photo postcards is that they are often devoid of any descriptive text.
Collotypes, which provide the finest detail of all printing methods are sometimes confused with real photo postcards.
But even collotypes will exhibit a discernible grain when magnified.
At least 450 different real photo postcard backs can be found but as of this time there is a lack of accurate information regarding all their dates of use, or they were used in very limited quantities.