If you change the angle of the photo to a light source, the silvering will become stronger and darker, sometimes disappearing.It can range in intensity and often resembles a silvery patina.
Reprinted by Beijing's Three Shadows Art Center, his guides "Judging the Authenticity of Prints by the Masters" and "Judging the Authenticity of Photographs" were the first comprehensive books on the subjects published in China.
Real-photo postcards (sometimes called RPPCs) are the result of developing a negative onto photo paper with a pre-printed postcard backing.
The key is silvering is an aging process and appears after decades.
The presence of silvering is strong evidence of a real photo postcards old age.
Amateur photographers were now able to have their own images printed directly onto postcard paper and send them through the mail.