Most of us pay very little attention to the envelope – it's just a throwaway piece of office stationery. Yet some people pounce on them, not because they're waiting for some amazing piece of good news in the post, but because they're fascinated by the geometric patterns printed on the inside.
The security pattern is a direct descendant of the window envelope, which was invented by Americus Callahan in the USA in 1901. The window was a labour-saving device, but it also meant that peeping toms could sneak a peek at what was inside. So in 1903 the Transo envelope company came up with the idea of tinted interior, and this curious form of op art and camouflage was born.
More than 100 years later, the security pattern is alive and well, and can be seen not only inside envelopes but gracing other more visible office items. Take a look at these pencils
and these rolls of old-fashioned gummed tape
