Antique Hold-To-Light Postcards

I never knew such things existed until I happened on them in Clive Thompson's Linkfest.

From reddit:

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I started collecting these cards several years ago when I was really interested in collecting antique Coney Island postcards.

Each of the cards has been intricately "carved" out and painted with bright colors allowing those areas to glow when held up to the light, the thicker parts of the paper don't let any light through.

All of the cards pictured are from the early 1900s, most likely between 1903 and 1910, because two of the cards I have depict the 1904 St. Louis World's Fair, and 2 of the 4 Coney Island cards pictured depict an area of Coney Island called Dreamland which burned down in 1911.