Developing Agents--pH Profile

[lensmagic]

Harvey W. Yarow, Ph.D., writes that each developer has a pH profile (citing Dickerson, Mees), so that it is effective within a certain range, usually dependent upon its ionization constant(s). Does anyone have any information on this concept? I infer that certain developing agents are suited to certain pH ranges, so that changes in contrast might best be obtained by employing different developing agent/alkali combinations.

 

[Alan Johnson]

"pH profile" - what means that?
Theory of the Photographic Process 3rd ed has 4 pages relating to the effect of pH on developing agents.

 

[Photo Engineer]

The effect of pH on developing agents = pH profile. They are essentially the same concept in simple terms.

The reduction potential of any developing agent changes as pH changes, and therefore most become inactive at one pH and very active at another. An example is Amidol which is very active even if the pH is acidic, and HQ which is nearly inert when the pH is acidic.

See Mees, Mees and James or Haist for examples.

PE

 

[lensmagic]

The effect of pH on developing agents = pH profile. They are essentially the same concept in simple terms.

The reduction potential of any developing agent changes as pH changes, and therefore most become inactive at one pH and very active at another. An example is Amidol which is very active even if the pH is acidic, and HQ which is nearly inert when the pH is acidic.

See Mees, Mees and James or Haist for examples.

PE

I found a copy (they are scarce) of Haist for $390! I found a copy of Mees & James for a mere $250. Let me just observe that metol apparently works well with sodium sulfite (think D-23) and sodium carbonate (think Ansco 120). That's a pretty big swing on the pH scale.

 

[Photo Engineer]

I found a copy (they are scarce) of Haist for $390! I found a copy of Mees & James for a mere $250. Let me just observe that metol apparently works well with sodium sulfite (think D-23) and sodium carbonate (think Ansco 120). That's a pretty big swing on the pH scale.

I believe that you can get a brand new copy of Haist for less than that from Grant himself. As for Mees, or Mees and James, those are exorbitant.

PE

 

[Alan Johnson]

"The Theory of the Photographic Process" 3rd ed by Mees and James is currently secondhand at amazon.com for $30-$35.