Perceptol - Data Sheet Question

[bvy]

This is from the Perceptol data sheet, development times for HP5+. It seems like this should be the other way around -- a stock recommendation for 320, and a diluted recommendations for 250 (a lower EI). You can see that pattern in the times for the other developers, and I thought it was true in general.

Is it something peculiar about this developer, and shooting below box speed?

 

[Anon Ymous]

No, the datasheet is right. Perceptol is a super fine grain developer, but this fine grain comes at a speed penalty. When used dilute, grain becomes somewhat coarser (but still fine), but the speed penalty is also reduced.

 

[Ian Grant]

It's because it's a Metol based developer (no second developing agent) high in Sodium Sulphite (100g/l) which restrains the Metol lowering the effective film speed, as soon as you dilute to 1+1you've diluted the Sulphite (to 50g/l) and the Metol despite alo being more dilute is far less restrained.and you get a slightly higher effective film speed (EI).

Ian

 

[bvy]

Both good explanations. Thanks.

 

[Gerald C Koch]

Ian and Anon are right. What people fail to grasp is that when you dilute a developer you are not only reducing the amount of developing agent(s) BUT ALSO EVERYTHING ELSE in the formula; halide solvent, restrainer, alkali, ... You cannot makes guesses based solely of the reduction of the developing agent.