Whiteboard
Whiteboards became commercially available in the early 1960s, but did not become widely used until 30 years later. Early whiteboards needed to be wiped with a damp cloth and markers had a tendency to leave marks behind, even after erasing the board. Dry-erase markers for whiteboards were invented in 1975.
Black Jack (stamp)
After the War was over, poverty inspired people to wash off the cancellation from the stamps and attempt to use them again. The Government then decided to put an antitheft device onto the stamps known as a grill. This grill, which consisted of various rows of tiny indentations into the stamps, was supposed to make it impossible to wash off the cancellations without being detected; but people usually got around this by bisecting the stamp, and then reusing that portion that didn't have a cancellation on it. The first grill applied to a Black Jack stamp is known as the "Z" grill, introduced in January 1868. Over the next few months, the Post Office successively employed three smaller grill patterns (D, E and F) in the production of this stamp.