[CrimpJiggler]

I got a sudden obsession with photochemistry and need to know all about it so silver seems the place to start. I read (although I can't find any youtube videos showing it which pisses me off) that photography all began when a scientist accidentally discovered that silver nitrate turns black when exposed to bright light. I've seen white silver chloride solution turn black when exposed to light and I hear that yellow silver bromide turns purple when irradiated. What reaction(s) does the light trigger in these silver salts and what are the products? For instance what is the black stuff that forms when silver nitrate is irradiated with sunlight? I know silver oxide is black, is that what it is? Then what about the purple stuff that silver bromide turns into?

[Arkcon]

http://en.wikipedia.org/wiki/Latent_image

Briefly, exposure to light results in the photoreduction of tiny amounts of the silver halide crystal into free elemental silver.  Kinda logical, when you think about it.  The compounds of less reactive metals, like platinum, gold, silver, copper, and mercury are easily reduced, sometimes by surprising circumstances, say a trace of organics in a "pure" distilled water sample.  You can browse around more on Wikipedia, for the history of photography using mercury exposed silver copper plates, and how color photography can use the latent image to sequester dyes.

[CrimpJiggler]

Thanks, the wiki page on latent images is explaining everything I'm wondering at the moment.