Someone mentioned once that they added sodium sulfite (maybe sulfate)to their developer and was able to increase development time. Does anyone know why increasing development time would be advantageous and if adding this chemical is useful. I think that it slows down oxidation (not sure). In particular I use HC110 (B) diluted 1:14 for 10 min at 68 deg. thanks for any input. carol

-- carol maurin (cbmaurin+@pitt.edu), February 29, 2000

Answers

Yes, sulfite is a componant of several developers. One of its activities is to act as a reducing agent to keep the developing agents reduced so they can then reduce the exposed silver (lots of reduction going on there huh?). Another action that sulfite has is as a silver solvent. It's solvent activity is towards the metalic silver in the emulion. It basically disolves the surface of the developed silver grains changing their structure and look. The disolved silver can redeposit elsewhere on the silver grains again altering them. This activity occurs at high concentrations of sulfite, beyond that necessary for the preservative activity. A good example of a developer that uses both of these activities of sulfite is D76. Undiluted D76 is a highly solvent developer. Diluted 1:1, the sulfite concentration is decreased enough to decrease the solvent activity and the negatives have an entirely different character (are sharper and have more grain).

Get your self a copy of Steve Anchell's Darkroom Cookbook and a copy of Steve Anchell and Bill Troop's Film Development Cookbook. They will give you all the information you could possibly want or need about componants and formulations of developers and other reagents used in photography.

-- Fritz M. Brown (brownf@idhw.state.id.us), February 29, 2000.

Sodium sulfite sort of helps uncover development sites on the grains and can help increase film speed; it doesn't take much. For example, HP5+ in Rodinal 1:50 gives EI 200, but with the addition of 20g/L sodium sulfite the EI increases to 320 for the same CI.

Larger amounts of sodium sulfite acts as a solvent, nibbling away at and smoothing the edges of grain clumps (the "grain" you see) but this has the effect of decreasing acutance.

I can't think of anything that sodium sulfite could do to let anyone increase development time other than work as a preservative; that might allow a longer time with a developer that otherwise dies due to oxidation during development. But if the point of a longer development time is to increase contrast, a simpler solution would be to use a stronger developer.

-- John Hicks (jbh@magicnet.net), March 01, 2000.

Like Mr. Hicks, I can't imagine that adding sulfite would increase developing times--since it would tend to increase ph slightly, it might even decrease development times. And most modern films don't require a "fine grain" developer.

-- (edbuffaloe@unblinkingeye.com), March 02, 2000.

I wonder whether sulfite would be an active enough reducing agent to help recycle the developing agent in a very dilute compensating developer, thus allowing a longer development before it totaly exhausts. Maybe this is what Carol is refering to.

-- Fritz M. Brown (brownf@idhw.state.id.us), March 02, 2000.

Mea Culpa. I stated in my first post above that sulfite is a solvent of metalic silver. Apparently I had my brain disconnected and fully in neutral when I said that. Sodium sulfite is a solvent of silver halides. It dissolves the undeveloped silver, not the metalic silver. This solvent activity erodes the grain structure of the film and softens the edges of the grain. The disolved silver can also redeposit on the grains, again softening the structure of the grain. Sorry for the confusion .

-- Fritz M. Brown (brownf@idhw.state.id.us), March 03, 2000.

I have only tried this with Edwal FG7 and it yeilds higher emulsion speed and improved highlight detail. I use it exclusively with infra- red 35mm where highlight detail is so easily lost. It makes a good developer when push processing older technology 35mm films like tri-x and hp5. I never considered the ability to extend developement times an asset in and of itself, I'm always trying to figure ways to shorten developement times... t

-- tom meyer (twm@mindspring.com), March 05, 2000.

Sodium sulfite added to FG7, 9% reccomended, increases speed of film and REDUCES substantially the development time! I have tested with densitometer film speed and development times for FG7 with and without the Sodium Sulfite. There is at least a 1/3 increase in film speed with SS and a 40% reduction time for development. I am shooting HP5+ developed in 5 reel patterson tank with inverse agitation. My development time for HP5+ with SS is 6 min rated at 400EI; without SS 11and1/2min rated at 320EI. Amazing I think! Sodium Sulfite acts as both a preservative preventing Oxidation and also as a developer; sounds contradictory, but that is what it does! Hello to all you RIT GRADS who remember Materials and Procceses with Prof Stroebel.

-- John Elder (celder2162@aol.com), December 13, 2001.