Cyanotype is often learnt on a sheet of paper, but Prussian blue clings to many other materials: cotton and linen of course, but also wood, glass, ceramics, stretched canvas and even a pebble picked up on a beach. The process does not change from one support to another; it is the material that decides what is easy and what needs a primer.
This page gives an overview of the supports that accept sensitising, the common principle that links them and the specific point that changes each time, and refers you to the dedicated pages for the detailed method for each material. The reference guide to cyanotype puts the process as a whole in context before tackling this question of the support.
The principle common to all supports
Before comparing materials, you need to understand what never changes, because this foundation explains why cyanotype adapts to so many surfaces. The process relies on two iron salts, ferric ammonium citrate and potassium ferricyanide, mixed in equal parts to form a light-sensitive solution. 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.
What happens under UV
Under the UV from the sun, iron in oxidation state III is reduced to iron II, which then reacts with the ferricyanide to form Prussian blue, a deep pigment that is insoluble in water. Where an object or a negative has blocked the light, the iron has not reacted and washes away in the rinse, leaving the original colour of the support, and this contrast between the exposed blue and the light reserved areas draws the image, whatever the material.
The decisive point lies in that word, insoluble. Prussian blue forms right on the surface and stays attached to it, which means it can form on anything that holds the iron solution for a moment and lets it dry. The real question, then, is not whether a material accepts cyanotype, but how to get it to hold the solution long enough for the reaction to take place.
Porous supports take hold naturally
The most generous family is that of porous materials, which soak up the solution and hold it in their thickness without any preparation. Paper and fabric are its two classic representatives, and they are where you learn the process.
A watercolour paper of sufficient weight absorbs the solution like a sponge, holds it while it dries and stands up to the final rinse without falling apart, which makes it an ideal training ground.
The natural fibres of textiles, cotton, linen, hemp and silk, behave in the same way, except that fabric then goes through washes, which adds a requirement for fixing.
Beyond these two well-known supports, other porous materials take the blue without much difficulty. Raw wood, unvarnished, soaks up the solution through its open fibres and gives warm blues where the pigment settles into the grain and the figure of the board, a look all its own.
Work on a pale, sanded wood, plywood, poplar or birch; the complete method is on the page about cyanotype on wood.
Stone follows the same logic, and a pebble picked up on a beach is a readily accessible example. A limestone rock or a pale, matt, unpolished pebble holds the solution on its rough surface and gives a printed object you keep as a memento, and the page on cyanotype on pebbles and stone details how to choose the stone and how to press things flat on a domed surface.
The more polished and closed the stone, the less it takes hold, which brings us back to the principle: a surface that soaks things up welcomes the blue without preparation, and you simply give it a little more solution than a sheet of paper.
Smooth supports need a primer
Then comes the other large family, that of closed, non-porous surfaces that hold nothing by themselves: glass, glazed ceramics, metal or plastic. On these materials, the solution slides off, beads up and dries in uneven puddles, and the blue does not survive the rinse.
The answer comes down to one word: primer. First apply a bonding layer, most often a thin film of hardened gelatine or a suitable medium, which creates a porous skin able to hold the iron solution as paper would. Once this primer is dry, sensitise over it as on a conventional support, and the blue forms in this intermediate layer rather than directly on the glass.
Translucent results on glass
This is the technique that lets you print a cyanotype on a backlit glass plate or on an earthenware tile, and it opens up translucent results that are impossible on paper.
The primer, how it is applied and the exposure are set in detail on these surfaces. The principle also applies to unglazed ceramics, whose porous fired clay sometimes takes hold directly when the bisque has not been glazed.
Canvas and artists' supports
Between soft fabric and the rigid panel lies the painter's stretched canvas, which combines a natural fibre and a surface preparation.
A raw cotton or linen canvas, not primed with acrylic, behaves like a textile and soaks up the solution without difficulty, whereas canvas sold already prepared poses the opposite problem: its acrylic gesso forms a closed layer that repels the water-based solution, a little like varnish on wood.
So choose a raw canvas to sensitise directly; this in-between position sums up the whole overview well. Faced with a new material, watch how it reacts to a drop of water. If the drop soaks in, sensitise it like paper; if it beads up, you need a primer before anything else.
What really changes from one support to another
Once the solution has taken hold, three points set the supports apart from one another. The first is the amount of solution: a thick material such as wood or canvas soaks up more than a sheet of paper, and you need to plan for a more generous coat to avoid dry patches that come out pale.
The second is the contact between the support and the object or negative. On a flat, rigid surface, pressing everything under glass is easy; on a soft fabric or a domed pebble, it becomes the tricky point, because the slightest gap lets light through and blurs the outlines.
The third is how it stands up to water, as the rinse has to stay gentle enough not to strip the pigment from a fragile primer. Everything else stays the same: the chemistry is identical and exposure in the sun follows the same rule everywhere, from a few minutes in full summer sun to several tens of minutes in overcast weather, with no absolute figure, the cue being the colour change on the surface that signals sufficient exposure.
Three points to adapt to the support you choose:
- Amount of solution: wood or canvas absorb more of it than a sheet of paper.
- Contact: a flat, rigid surface makes it easier to press everything flat; a soft fabric or a domed pebble makes it harder.
- Rinsing: keep a gentle enough touch not to strip the pigment from a fragile primer.
Where to start, depending on your project
Faced with this variety, the right support is the one that serves your image and your level. To learn, stay with paper, which is forgiving and needs no preparation, then move on to fabric when you want an object that can be used and washed.
Wood and pebbles come next, accessible as long as they are raw, for anyone who likes textured results and one-off objects. Glass and ceramics remain the most demanding, best kept for when you have mastered the primer, and this progression from porous to smooth is also a progression in difficulty.
For all these supports, the Sténoflex cyanotype kit brings together the two bottles of iron salts, pipettes and the instructions, the same solution being used to sensitise paper, cotton, raw wood or a primed surface. The process remains the same everywhere as at the start, getting the solution to take hold, exposing to UV and rinsing, and it is this consistency that makes cyanotype such a free process in its choice of surfaces.
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.
Compare the materials before you start, from absorbent paper to smooth surfaces that need preparation.