Firstoff, the major change is due to absorption of CO2 from the atmosphere which drops the pH as the developer keeps. This is due to the following: Borate and Carbonate love to buffer in the range of about 9.5 - 10.5 depending on the mix you have going. More Borate or Carbonate don't change pH much, this would only change buffer capacity, so you need to add something like Sodium Hydroxide.
Now, this increase takes us away from the buffer point of Borate or Carbonate, and so the developer is less stable from a pH (and therefore contrast) standpoint and our goal is higher contrast.
To get a high pH developer, you use Trisodium Phosphate as buffer and this works at about 11 - 11.5, but then the developer is still not as stable as you want due to Carbon Dioxide in the air.
That is about it, stability to pH changes is what I referred to, and since high pH is the element I suggested, you can retain activity simply by checking and adjusting the pH if it starts to drift. This is, in fact, what is done to control E6 color developer (pH ~11 with phosphate) and Kodachrome developers when they drift. They are essentially high contrast color developers that force the reversal development to completion.
The high contrast B&W developer, D8, has almost 40 g/l of Sodium Hydroxide and it is loaded with Hydroquinone. Both are known as being able to yield high contrast results. It has however, low buffer ability when compared to most other developers.
Last edited by Photo Engineer; 04-23-2008 at 05:29 PM. Click to view previous post history.