Hidden word with erasing link

Write a word, symbol or number combination in marker and fill in the clue with an erasable marker to hide it. 

Does it require an electronic device? No

With a chalkboard (or slate), the indelible message is made with paint, pen or roller pen.
After drying, the message can be filled in with chalk or covered over. This technique can also be used on rock, walls or breeze blocks…
A similar result can be obtained with a whiteboard, a permanent marker and a dry-erase pen.

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