Perceptol Formula
 

Interesting. I never knew what the formula was, but in hindsight should have guessed. The sharpness comes from the metol, obviously - metol is known for it's sharpness. The one stop loss in speed when using Perceptol comes from the fact that metol is the sole developing agent. In most developers it would be mixed with Hydroquinone to make a super-additive developer, and maintain the speed. Nevertheless, it is a fine developer, and I have used it often. Just didn't like losing speed...

THe strange thing is that for almost all film speeds, Perceptol has dev time for EIs that are at least 1/3rd stop less or more usually one stop less. Then you get to D3200 where it lists time for box speed. OK I know that D3200's real speed is said to be about 1000-1250 but yet Perceptol allegedly "works at EI 3200.

How are these seemingly contradictory situations reconciled i.e. no times for slower films at box speed and yet a time for Ilford highest speed film at its highest speed?

Mike

are you saying those speeds are obtained or that they are claimed.

That's interesting Pete. Most of the rumours regarding the composition of Perceptol have suggested that it is D23 with 30g of Sodium Chloride. Well that's just about correct except the Sodium Tripolyphosphate. Anyone know what this does?

This is a great developer when used at 1:3 – try it with HP5 it could surprise you.
Found out some years back when reading (Barry Thornton – Elements 1993. page 72/73)
David.

You mean it doesn't come ready mixed in a bottle? :eek:

I had to think about that one - slow today, late night.
David.

If you do not buy the packet Perceptol and make it up yourself you have to be careful to use pure Sodium Chloride as ordinary salt contains traces of Iodine which is a powerful restrainer ( See Crawley's FX1 Formula where he proposes a 0.1% Potassium Iodide addition!).

Most big chemical producers, besides using the normal developing agents, will add various chemicals to try to overcome the huge differences in tap water around the world. Tripolyphosphate is one of those chemicals. You can safely leave it out if you're mixing your own.