Quote (chantal7 @ Sun, Feb 22 2009, 03:35am)
I don't really understand this one ^^
From Wiki.
Quote
Silver halides are used in photographic film and photographic paper, as well as radiographic film and paper, where silver halide crystals in gelatin are coated on to a film base, glass or paper substrate. The gelatin is a vital part of the emulsion as the protective colloid of appropriate physical and chemical properties. Gelatin may also contain trace elements (such as sulfur) which increase the light sensitivity of the emulsion, although modern practice uses gelatin without such components. When absorbed by an AgX crystal, photons cause electrons to be promoted to a conduction band (de-localized electron orbital with higher energy than a valence band) which can be attracted by a sensitivity speck, which is a shallow electron trap, which may be a crystalline defect or a cluster of silver sulfide, gold, other trace elements (dopant), or combination thereof, and then combined with an interstitial silver ion to form silver metal speck.
The size of the silver halides is what causes film grain, also, their shape, hence TMAX film, because the grain is T shaped.
Quote (jmw3407 @ Sun, Feb 22 2009, 03:49am)
well my family owned a newspaper for 40 years so i grew up around black and white photography. film that is. when i was a little kid i used to take a handfull of pennies and drop them in the developer for the photographic paper. the pennies attract the silver that comes off the pictures during the developing process. the silver sticks to them and then they stay that way till u rub all of it off. it only works on moderately used developer not new. the thing is when you develope a black and white print the picture is actually made up of tiny silver particles they picture is formed when little pieces of the silver come off and your photo shows up. then when it develops to a certain point you put it in stop or fix to stop any further developing. this all must be done ina dark room.
Just like simple electrolysis experiments in school. Get a powerpack, connect the positive to one penny, connect the negative to another, dip the two pennies into copper sulphate solution, making sure they don't sure they don't touch. The cathode will start being coated in pure copper.