Why was silver necessary for photography?

If you coat some paper with silver chloride and expose it to light, you will find out that the silver chloride will turn black where the light falls on it. If you cover it with something like a leaf, the part covered by the leaf will remain white.

If compounds of silver like silver bromide, silver chloride or silver iodide are exposed to light, they break down to form tiny particles of silver that look black. An English scientist called William Talbot used this reaction to make photographs.

To develop a photograph, a thin layer of silver bromide is deposited on a sheet of photographic paper, and exposed to light. This produces a negative image from which the photograph is printed. Digital photography succeeded this technique which is no more in use now.

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