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Old 7th June 2012, 09:23 AM
S Nicholls S Nicholls is offline
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Default Fx-1

This appears to be a very simple developer yet it performs remarkably well. I have posted a similar thread on LFF recently and the answer provided was a good generic answer but really doesn't address why the developer performs the way it does.

I'm using the concentrated version of the formula @ 5+5+10 to give 60 mls for BTZS tubes. The results are razor sharp and tonality is excellent but I'm getting a very genuine speed increase of a stop or a bit more using Foma 200. [Arita Edu Ultra 200]

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 formula does what it does?
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  #2  
Old 9th June 2012, 09:46 AM
Lostlabours Lostlabours is offline
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The Iodide had an effect on the sharpness with the older emulsions of the era but with todays films you can leave it out.

Ian
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Old 22nd June 2012, 03:03 PM
Dwane Dwane is offline
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"...why such a formula does what it does? "

FX-1 is an acutance developer. A working solution of FX-1 can be described as being a dilute solution of an active developer. Being dilute means only the silver halides near the surface of the emulsion will be developed before the developer is exhausted. Being active insures that enough silver halide is developed to insure a printable negative. The accutance is a result of the light not being scattered very much when passing thru the thin layer of developed silver halides. Fast films have a thicker emulsion, thus causing a greater scattering of the light as it passes thru the thick emulsion, thus resulting in less acutance.

Other acutance developers are Beutler's (which was the first), FX-2, FX-13, and Mason's. They are quite alike in composition, containing only metol, sodium sulfite, sodium carbonate.
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