ELI5: Why does putting clear (scotch/packing) tape on a frosted window let you see through it?

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Frosted glass is simply glass with a (chemically) roughened surface which causes the light passing through the pane to diffuse in all directions, instead of letting straight through. (Scotch) tape is essentially a clear plastic surface coated with a thin layer of transparent adhesive. When you stick it to frosted glass the adhesive fills the small cavities on the glass surface which were made by the chemicals used to frost it. The adhesive thus smoothens the surface, counteracting any diffusion. This also means that the tape trick only works on chemically frosted glass, or mechanically frosted glass with a fine texture, because the thin layer of adhesive can only smoothen out relatively small cavities in the glass. Edit: thanks for the silver! Edit 2: and thanks for the double silver and the gold!!

KvantumKvak

So I could de-frost my bathroom windows with patterned privacy tape, and just the frosted parts of the patterned tape would be visible? If that makes sense Edit: auto correct issue

acoustic_girl

The adhesive on the tape fills in the rough surface smoothing it out allowing light to travel through it without scattering

YoungDiscord