Why is it so??

[Shen45]

FX-1, an extremely simple developer, Metol based - Sodium Sulphite Sodium Carbonate and Potassium Idode. I'm probably not getting the full potential from the developer by using BTZS tubes but it is razor sharp, excellent tonality and a genuine speed increase. So my question why is it so.
What actually makes this a unique developer. I used it with Foma [Arista Edu Ultra] 200.

Steve

[Jay DeFehr]

Steve,

FX1 is a close cousin to Beutler's, the classic acutance developer.

FX1 working solution

Metol 0.5g
Sodium sulfite 5g
Potassium Iodide 0.005g
Sodium carbonate 2.5g

Beutler's working solution

Metol 1g
Sodium sulfite 5g
sodium carbonate 7.5g

Compared to Beutler's, FX1 is more dilute.

Beutler's 1+1
Metol 0.5g
Sodium sulfite 2.5g
Sodium carbonate 3.75g

And FX1 contains potassium iodide, a powerful restrainer. The differences between the two developers are intended to create edge and compensating effects in FX1. While we're comparing, I'll include Obsidian Aqua:

OA working solution

Catechol 0.5g
Potassium metabisulfite 0.04g
Potassium carbonate 6.66g

Clearly, these are all birds of a feather, and represent different approaches to pursuing the same, or similar goals. So, if FX1 is unique, it's because it includes potassium iodide, while most acutance developers don't include restrainers.

[Shen45]

Thanks for the reply Jay,

I wonder if the Potassium Iodide in such small concentration is doing something other than act as a restrainer. If it acts as a restrainer why is there a genuine - over 1 stop - speed increase?

Is it such a minute amount that it really has no affect at all and is just to differentiate from similar formula? Or could the minute amount be working as a sensitiser as opposed to a restrainer.

The following is the formula I used [Jacks formula site] which is a 2 part concentrate as such. I mixed 5A +5B +50 water [the amount needed for 60ml in a BTZS tube]

STOCK SOLUTION A
Chemical Amount Units
Distilled Water 900 ml
Metol 5 g
Sodium Sulfite (anhy) 50 g
Potassium Iodide Solution, 0.001% 50 ml
Distilled water to make 1000 ml

Place 900 ml of water in the mixing container and add a pinch of the sodium sulfite. This small amount of sulfite minimizes the initial oxidation of the metol. If more sulfite is added at this point the metol will not dissolve. Add the metol to the solution and stir the solution to dissolve the metol. Add the sodium sulfite and again stir until dissolved. Next add 50 ml of the potassium iodide solution, 0.001%. Stir the stock solution, then finally add sufficient water to bring the total volume in the container up to 1000 ml. Stir the solution to ensure it is mixed thoroughly. Transfer the Stock Solution A to the brown bottle.

STOCK SOLUTION B
Chemical Amount Units
Water (90°F/32°C) 900 ml
Sodium Carbonate (anhy) 25 g
Water to make 1000 ml

Over on APUG Ian Grant posted this material

"Crawley published FX-1 as a one or two part developer

The 2 part is

Part A
Metol 5gm
Sodium sulphite (anhyd) 50gm
Potassium iodide .001 soln 15ml
Water to 1 litre

Part B
Sodium carbonate (anhyd) 25gm
Water to 1 litre

To use 1 A + 1 B + 8 water

The 1961 version uses 50ml KI by 1972 Crawley was publishing the Formula with only 15ml KI, modern emulsions contain higher levels of KI so its possibly not so critical.

Ian "


Maybe if you see this Ian you can add to the discussion as to why such a simple formula does what it does?

[Bill Burk]

I wonder if the Potassium Iodide is not actually doing anything... except keeping the Potassium Iodide that is already in the emulsion from leeching out by osmosis during development... So whatever it is there for in the first place, it does a better job of it.