This includes virtually all invisible inks, but pure distilled water can also be used in this way. Application of any fluid will disturb the paper surface fibers or sizing.
Fumes created from heating iodine crystals will develop the writing, which will appear brown because the iodine sticks preferentially to the disturbed areas of the paper. Exposing the paper to strong sunlight will return the writing to its invisible state, as will using a bleach solution.
Slightly dampening paper with a sponge or by steam and then drying it before writing a message will prevent writing from being developed by this method, but overdoing dampening will result in telltale paper cockling.
Fumes created from heating iodine crystals will develop the writing, which will appear brown because the iodine sticks preferentially to the disturbed areas of the paper. Exposing the paper to strong sunlight will return the writing to its invisible state, as will using a bleach solution.
Slightly dampening paper with a sponge or by steam and then drying it before writing a message will prevent writing from being developed by this method, but overdoing dampening will result in telltale paper cockling.
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