1855 - 20c dark blue, I Issue, ’59 printing, from

 1855 - 20c dark blue, I Issue, ’59 printing, from ‘MILANO 28 DIC 59’ to Casale. Extremely rare letter sent by the Milan Institute for the Blind, written with a special machine using text composed of dotted characters, predating the invention of the system devised and introduced by Braille. The earliest known document with dotted writing for the blind to have passed through the post. Rarity. Detailed E. Diena certificate (Sassone 15B)