Cyanotype, reversal slides and other things you can do with a bottle and the sun

Before there was film there was paper with chemicals brushed on it, and the sun. Those processes never went away; they moved to kitchens and art schools. Two are worth your weekend: the cyanotype, because it needs two chemicals, paper and daylight, and black and white reversal, because it turns a roll you already know into slides.

Cyanotype: the blue print

Mike Ware's history is short: Sir John Herschel devised the cyanotype in 1842, mixing strong solutions of ammonium iron(III) citrate and potassium ferricyanide, and it was "the first successful non-silver photographic printing process" ². Brian Young's history at AlternativePhotography.com puts it in company: Talbot's salt prints of the 1830s, paper soaked in weak salt solution and coated with silver nitrate, came first, and the cyanotype's iron chemistry was the cheap, stable cousin ⁴.

The classic formula, as Malin Fabbri lays it out, is two stock solutions. Solution A: 25 g of ferric ammonium citrate, the green kind, dissolved in water and made up to 100 ml. Solution B: 10 g of potassium ferricyanide, made up to 100 ml. Mix each in about 80 ml of water first, then top up; keep them in separate brown bottles and combine equal parts only when you are ready to coat ¹. Brush the mix onto watercolour paper in dim room light, dry it in the dark, lay a negative or an object on it under glass, and put it in the sun. The exposed areas go from yellow-green through blue to a bronzed grey; wash in water until the yellow unexposed sensitiser is gone and the blue develops as it dries. Minutes in summer sun, longer in winter, and the test is a strip under a coin.

Ware's "new cyanotype" replaces the citrate with ammonium iron(III) oxalate because it is more light-sensitive and not attacked by mould, and the ingredients of his sensitiser are 30 g of the oxalate, 10 g of potassium ferricyanide and 0.1 g of ammonium dichromate in 100 ml; it is not a mixing recipe, because the preparation is staged, hot, with a crystallisation and filtration his page describes step by step, so treat the quantities here as the summary and his page as the method ². It gives a longer tonal scale and shorter exposures; it also contains a dichromate, which is a sensitiser and a carcinogen, so it is the recipe for people who already handle chemistry with gloves, goggles and a sink nobody eats from.

Reversal: a slide from a negative film

Ilford publishes a complete method for making black and white transparencies from its negative films, and it reads like a dare. The films: Pan F Plus is "particularly recommended" for bright, high-contrast positives; FP4 Plus and Delta 100 can be used; HP5 Plus and Delta 400 are not recommended because the contrast comes out too low ³. Exposure must be accurate, and Ilford's tests found one stop of extra exposure over the box speed a good starting point, which means setting the meter to half the box speed ³.

The baths, from the sheet ³:

1. First developer: PQ Universal diluted 1+5 with sodium thiosulphate crystals added, 8 g per litre for Pan F Plus, 12 g for FP4 Plus and Delta 100. Twelve minutes at 20 °C as a starting point. The hypo is there to clear the highlights; the sheet says to adjust the time to taste.
2. Wash 5 minutes in running water.
3. Bleach: equal parts of solution A, 2 g potassium permanganate in 500 ml of water, and solution B, 10 ml of concentrated sulphuric acid in 490 ml. Mixed fresh for each film, used for 5 minutes with continuous agitation, or until all the silver image is gone. The bleach is strongly acidic and stops development at once; after it, the rest can be done in room light.
4. Wash 1 minute.
5. Clearing bath: 25 g of sodium or potassium metabisulphite per litre, 2 minutes with gentle inversions, to remove the staining the bleach leaves behind, which the sheet describes as yellow.
6. Wash 1 minute.
7. Second exposure: the film off the reel, both sides, 30 to 60 seconds at 46 cm from a 100 W tungsten lamp or 30 cm from a fluorescent tube. Two to four times that is safe; too little leaves the slide thin. Not sunlight.
8. Second developer: PQ Universal 1+9, freshly mixed, 6 minutes at 20 °C, in room light, to develop all the remaining halide fully. Then fix for 5 minutes in Rapid Fixer 1+4, wash 10 minutes in running water, rinse and dry ³.

What happened: the first developer made the normal negative; the bleach dissolved that silver and left the unexposed halide untouched; the fogging exposure and second developer turned that halide into a positive. The sheet's warnings deserve repeating. Concentrated sulphuric acid is dangerous; Ilford's sheet offers an alternative for anyone who cannot get it, a 10 per cent solution at 100 ml to 400 ml of water for solution B ³. The sheet does not say whether its ten per cent is by weight or by volume, so follow the sheet and ask your supplier how their solution is made before you rely on it. The bleach softens the emulsion, so Ilford suggests a hardening fixer may help, and gloves throughout ³. Project the result on a wall and you will understand why people bothered.

And the rest

Salt prints, Van Dyke brown, platinum and palladium, gum bichromate, wet plate collodion, which must stay wet from coating through development: each has its own literature, and AlternativePhotography.com, which has covered these processes since 1999, is the place the practitioners publish ⁴. The pattern is always the same: a light-sensitive salt, a carrier, a light, a wash. Salt, Van Dyke, platinum and gum are contact-printed under a negative like the cyanotype, each with its own developing and clearing baths; wet plate is exposed in a camera and developed, fixed and varnished on the spot. The only question is which chemistry you are willing to keep in the house.

Safety, again

Every chemical here is handled with nitrile gloves, splash goggles and ventilation; weigh powders where nothing stirs the dust, and read the supplier's safety data sheet for each one. Ammonium iron(III) oxalate is toxic and an irritant; ammonium dichromate is a carcinogen and a sensitiser; potassium permanganate is an oxidiser that stains and burns; concentrated sulphuric acid burns. Mix acid into water and never the reverse. Never acidify a ferricyanide solution and never let cyanotype waste meet the acid bleach: ferricyanide and strong acid can release hydrogen cyanide. Keep the baths and their wastes apart. The permanganate bleach and the dichromate sensitiser go to hazardous-waste collection; the used fixer, which carries silver, goes by the route your local rules give; nothing here goes down the sink. Lock it all away from children and pets.