Monday, April 6, 2015

thank you sodium sulfite.


sodium in general has taken over my life. sodium sulfite being the obvious guilty party in my darkroom, and sodium chloride being added everywhere in my food. i really don't like the taste of salt, and i restrain from smelling, or inhaling fumes, of sodium sulfite.  in any case, sodium sulfite is everywhere in silver printing. no really: everywhere. from beginning to end - it even used to be a preservative in food.  so this problem of oxidation made me think of how sometimes, when i look at a print, i see a list of chemicals necessary to the process. a long list, mind you. let's try to look at what goes where in silver photography: the magic of the image appearing in the developer is actually quite complicated, yet fascinating. and many of these chemicals can be quite harmful, to both people and the environment. the process is not to be taken lightly. osha recommends to just "water down" your chemicals into the drain, with enough water so it doesn't damage the pipes in the building. yep, that's an actual quote.
and i will not mention the several gases released from mixing powder, or by contamination. i have always known all this, my dad was an engineer and mathematician, an uncle a chemistry professor, and another worked in optics -kind of like oliver sack's "uncle tungsten" - i walk into my darkroom with a certain knowledge of chemistry, i understand where harm can come from, and a side effect is that the skin on my hands is very dry. can't really put cream on your hands to touch film and photo paper, it's chemically harmless, but visually awful.
anyway: sodium sulfite, sodium erythrobate, sodium metabisulfate, disodium tetraborate pentahydrate, pentasodium ethylenenitrilo tetraacetate, hydroxymethyl, phĂ©nitpyrazolidin. that is just a taste of x-tol. no hydroquinone you'll notice. and it's a great name, extol the virtues of this developer! but we forgot that film itself has to be manufactured first. acetate, i don't feel like going into details here, just acetate, and gelatin…  well, again, let’s just call it gelatin and concentrate on what gets mixed in with it, namely crystals.  and how does one get these crystals?  bars of silver are dissolved in nitric acid to form silver nitrate, and combined with bromide as an alkali salt, potassium bromide for example.  this results in light sensitive silver halides crystals.  mixed with gelatin it makes an emulsion, a silver halides emulsion. voilĂ .
why gelatin? it’s transparent, grainless, it’s a liquid when heated and gels when dry, yet it swells enough when in contact with liquid chemicals to affect halide crystals.
anyway, so you mix a solution of silver nitrate with a halide -any alkali metal halide-  say, sodium bromide -don’t forget the ammonium hydroxide, ammonium bromide, thymol and alcohol.  the emulsion maker may control the very size of these crystals and mix them over several layers.  the crystals get heated, ripening as it is called, they dissolve and crystallize again.  remember, within each crystal, the atoms are electrically charged (ions) and placed in a grid of sort by electrical attraction, with free-to-move silver ions, as well as important -to the latent image, and overall exposure- crystal imperfections.
so the film gets exposed -insert entire history of photography here- the silver ions interact with negative charges, a latent image forms, the bromide ions are neutralized to atoms, then absorbed by the gelatin.  next thing you know, you’re gently agitating at equal intervals…  the tiny silver deposits will be grown and amplified (a lot) to give a visible image.  the hydroquinone -or metol, or phenidone- and supportive agents including an alkali and a preservative start the process.  as you agitate the tank, electrons go for the exposed silver halides carrying silver atoms.  the developer gets full of potassium bromide and other chemicals without electrons.  developing time is over, everything gets rinsed in water and goes down the drain.  let’s skip over the temperature if you don’t mind…  also, you may decide the see the whole process with infrared, or a green light, and develop by inspection for even more control.
then it all needs to be fixed, made stable.  ammonium thiosulfate, boric acid, acidic acid, and again, sodium sulfite.  residual processing chemicals contain sulfur compound and will deteriorate the image if not washed properly.  ironically, a small amount of residual thiosulfate is needed against oxidizing agents.  all the unexposed, invisible silver halides get washed away in the hypo (fix). you can then recover the unused silver by electrolysis.
and don't worry: whatever grain structure is inherent in a film emulsion will be retained in the developed negative. do we even have to mention the energy of electrons, the speed of photons needed to get those latent silver atom specks? crystals are about 1 micron in diameter and contain about 10¹² silver atoms (or grains). you need an electron microscope to see these grains. my grain focuser only sees what we commonly call film grain, but is just really clumps of about 40 actual grains. long story short, we have a negative to print, more chemicals to gather and mix.
dihydroxy benzene, sodium carbonate monohydrate, hydroquinone and potassium bromide. the thing is that dektol makes my skin dry. perhaps then a mixture of sodium sulfite, sodium carbonate and hydroquinone, lpd powder developer seems to be better for me in the long run.
what type of wood was used to make the base of the paper? for our purpose perhaps it's best to just talk about the emulsion. although that was a concern of mine when ilford went from multi IV to the classic fiber paper. everything matters, any change at all changes things, not everything necessarily, but enough to make a difference. and yes, it is now a different wood being used for ilford papers. change is difficult in a field where consistency is a factor, but necessary in a technology-based environment. more layers of halides, all equally sensitive to blue on variable contrast paper, yet each differently sensitive to green. the halides are now being bombarded with yellow and magenta light. bam. negative film illuminated onto negative paper, silver halides into silver metal, reduction from salt to metal. and then it gets dipped in developer, the silver halides particles become metallic silver. stop. acidic acid. stop. sodium thiosulfate removes all untouched silver halides by turning it into a water soluble complex. wash with plenty of water, drain with plenty of water. the water is on all day. water water water.
and ventilation. plenty of ventilation.
all this solid state chemistry moved indoors before electricity mind you. velox emulsions are 500 times faster than albumen. photography was almost a hundred years old before an enlarger with a light bulb was brought into a darkroom as a regular practice. we are now way past the gaslight papers era, and exposed our perfectly evenly coated emulsion with a lightbulb (well, several halogens etc.). yes, you read right: gaslight paper. i'm glad i have electricity and mostly mixed chemical formulas where i just add water. it's very manageable for the everyday. i think twice before any exposure, i don't waste paper, i take the first guess very seriously, it's better for the environment.

1 comment:

Roberto LLerena said...

Excellent breakdown! At every lab I've worked at it seems, regardless of the silver recovery, filters, etc., that there is still plenty of harsh stuff going into the drain.