BUT the solution ear it will remain that much stronger and the reaction as fast. meawhile in thin regions of the neg, there's not a lot of tckled halide, it wont be n such a rush to react, and so wont oxidise or oxidse so fast. so the reacton in THAT area will start to slow down.

BUT as t does so, it will deplete the concentraton of the solution. BUT inside the tank, where you have dense regions on the negative that have had a lot of light, solution will come int contact with them and start to oxidise the halide quite quickly. remember, stronger the solution, less time the reaction needs. this is why times and concentrations get important. and NOT burn it all, but lea a pattern of un-burned sulfur in he ash! It's a bit like trying to set fire to a match-head. and hopefuly we have a picture rather than a black frame. but we don't want t ALL black, so we have to let the solution get to work, but stop it before it's finished. there's enough oxidsing agent it, to turn every bit of silver halide into silver oxide. we are trying, because we are actually relying on it to create a 'partial reaction'. what we want to do is, turn the sliver halide that has been partially oxidised by light into silver oxide, and NOT oxidize that which hasn't. we don't want to turn ALL the silver halide we have to silver oxide. In photography, however we are trying to 'cheat' the chemistry and deliberately NOT get a 'complete' reaction.

It's been two many years since I had to balance equations, and I haven't had enough coffee yet to do the maths, but you could, 'balance' the equation to put the correct proportions in so you have as much C,H&O on one side as other. only what you have to start, you have to have at the end, so while that equation describes the chemicals you start with, and what they get turned in to, it's not quite right as far as the quantities, because I started with CH4, which is one carbon and four hydrogen, at the end, I have one carbon in the CO2, but have lost a few hydrogen with only one in the H2O. you are actually deliberately trying to cause what in chemistry would be known as an 'incomplete reaction'įor example, chemical equation for burning methane, in oxygen, is CH4+O2=> CO2+H2O. in the tank, you are doing the same, 'boosting' that reaction, and getting tickled areas to turn black, and untickled ones to stay white.

Where light falls, it starts to oxidise, where it doesn't it doesn't. In the camera, making an actual exposure, you are trying to 'cheat' the chemistry where light falls it catalyses the oxidisation reaction of the silver halide emulsion.

In chemistry, rates of reaction are proportional, among other things, to temperature hotter the environment, usually the faster the reaction hence in colour processing the 'adjustments' for different bath temps then it is proportional to solution concentrations which s why in B&W you often have different dev times for mixing solutions at different strengths, say 3:1, 5:1 & 9:1.

Twizzle sticks with whistles