Postcards with cut-out windows
to be held up to the light
1.
Undivided Backs
By far the most elaborate WH postcards that I have seen are the early
ones; those produced up to 1903, where only the address could be written
on the back of the card.
Far simpler were the postcards produced from 1903 onwards with 'divided
backs' which allowed both the address and the message to be written on the
back of the card.