A red cyanotype is obtained through toning, never straight away: either by stopping a tannin bath early on a partly bleached print, which locks in a warm purple, or by laying a red dye such as a hibiscus infusion over the blue.
A cyanotype comes out of the rinse in its Prussian blue, and it is from this blue that you have to start if you want to reach red. No adjustment of the process produces a red print straight away, since the native colour remains blue; red, pink and purple are obtained only through toning, by transforming or covering the pigment that has already formed.
This page follows the route to warm tones that lean towards red and purple, without going round all the toners again. It follows on from our guide to cyanotype toning, which sets out the principle the baths share, and if you are new to the process, the complete cyanotype guide shows where toning comes in, right at the end, once the print is dry.
Why red is a difficult tint
Prussian blue readily shifts towards brown, grey and violet, but true red resists it, because no simple bath turns this pigment directly into red. Two routes let you get close: either push tannin toning to very warm browns that lean towards rust, or lay a red or pink dye over the blue, on top of it.
The tones you reach this way are warm reds and purples rather than bright, pure reds. The blue underneath always weighs in the balance, and it is from its meeting with a warm note that these tints are born, vibrant but rarely brilliant, which gives them a depth that a flat red lacks.
Looking at two dry test prints in subtle red-brown tones. The shade shown is not a promise of what a bath will give.
Purple through interrupted tannin toning
The first route goes through tannin, the same plant substance that gives the browns of tea toning. When you immerse a print in a tannin bath after partly bleaching it in an alkaline solution, the brown that settles in passes through an intermediate phase where it mixes with the remaining blue, and it is in this in-between stage that purples and reddish violets appear.
Taking the print out at the right moment
Everything depends on when you take the print out. A bath taken to the end tips into a frank brown, whereas a bath stopped earlier locks in a warm purple, still tinged with blue. This shade lasts only a handful of seconds, which is why you work by eye, ready to rinse as soon as the tint you want appears.
The detail of the two-bath sequence, alkaline then tannin, is covered in the article on tea toning, which serves as the technical basis here. The principle is the same, but it is stopping the second bath early that steers towards purple rather than brown.
Pink and red with a deposited dye
The second route does not transform the blue but covers it with a red or pink dye, just as you add a yellow to get a green. A concentrated infusion of hibiscus, red onion skins or certain dye plants lays a pinkish layer on the print over the blue, and the eye then sees a purple or a magenta-violet depending on the density of each of the two colours.
This layering logic is the same as the one that leads to the green cyanotype with a yellow, with red taking the place of yellow. It is more temperamental, because these red dyes adhere poorly to paper and are often fugitive, the pink fading with washing or with light much faster than tannin.
So you accept a degree of chance, with each plant and each paper giving a different result. For a first attempt, a short bath of very concentrated hibiscus on a well-contrasted print gives a fair idea of this route: a deep purple rather than a surface red.
Do not mistake an intended red for a damaged print
Not every warm tint is a successful toning. A cyanotype attacked by an alkaline product that is too concentrated or poorly rinsed can develop dull rust-brown stains that are only a sign of the pigment breaking down, not a red you were after. These accidents come with a loss of density and an uneven background, whereas controlled toning keeps the image sharp.
By contrast, the red you are after begins with a healthy, dense, evenly washed blue, which you work on with control. That is the condition that separates an intended warm tint from mere deterioration, and it always comes back to the quality of the starting print.
Keeping your red tones over time
Red and purple tints are among the most fragile in the cyanotype palette. Prussian blue on its own is one of the most durable pigments, but a purple obtained through interrupted tannin, and even more so a pink laid down by a plant dye, proves sensitive to light and can fade over time, with the print sliding towards brown or letting the blue underneath reappear.
So keep these prints with particular care, away from bright light and damp, framed behind UV-filtering glass if you want to hold on to the shade. That is the price of these warm colours, whose beauty rests on an unstable balance.
Where to start on the way to red
The more reliable route remains purple through interrupted tannin toning, because you adjust it by eye on a chemistry you already master with browns. Deposited red dyes come next, for those who accept their unpredictability, and it is by repeating short tests that you learn to recognise the moment when the purple is at its finest.
All of this first requires a sharp, well-contrasted Prussian blue, because no toning rescues a pale or poorly exposed print. To practise on solid foundations before going after red, the Sténoflex cyanotype kit brings together the potassium ferricyanide, the ferric ammonium citrate, the watercolour paper and the pipettes for your first prints, on which colour tests then make full sense. Potassium ferricyanide has low toxicity at the amounts used in the process, but it can release cyanide on contact with an acid, or under UV light when in solution.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. He has run introductory workshops in alternative photography, from pinhole to cyanotype, from the very beginning.