Angelo Taibi digs out a cyanotype formula to make the prints less contrasty.
The cyanotype process generally produces contrasty prints and for this reason the use of a low-contrast negative is often recommended. But, by reading the recipe of an old book of photography I found out that a print of low contrast can be obtained by slightly changing the conventional cyanotype method.
In the Book of Photography edited by Paul N. Hasluck (1905) the Ferro-prussiate Process is described on page 180:
"Prepare two solutions: (a) Citrate of iron and ammonia 1 oz., water 4 oz.; (b) Potassium ferricyanide 1 oz., water 4 oz. Coat any tolerably pure paper of fine texture with solution (a), using for this purpose either a broad flat brush or a tuft of wool.
The paper prints very slowly. The details should be brought out fully, and the dark parts should have a bronzed appearance. When a fairly dark brown image appears, (b) solution is applied by flowing it over the print. The result will be a picture in Prussian blue. The print is then passed through a weak solution of citric acid, washed for a few minutes in water, and hang up to dry in gentle heat."
It is worth noting that the method to prepare the two solutions is similar to the traditional cyanotype formula (although solution b is generally more diluted) but the coating and developing processes are very different! I then decided to follow these "new" instructions to produce my umpteenth cyanotype print by coating the paper with solution (a) and, after exposure, developing it with solution (b). After rinsing it in water, I got a low-contrast picture in prussian blue!
The print was then "developed" with solution (b) by using a brush in the same fashion of the coating process. It is important to always use different brushes for the two stages.
As an example, figure 1 shows the "bronzed appearance" of the print immediately after exposure to ultraviolet light. The print was then "developed" with solution (b) by using a brush in the same fashion of the coating process. It is important to always use different brushes for the two stages otherwise contamination occurs if the whole process is repeated, even after thorough washing of the brushes! Once the print appears fully developed (it is a matter of seconds), the usual washing procedure is applied. Figure 2 shows the final result and comparison with figure 3 – a cyanotype print obtained with the standard method – demonstrates a significant reduction in contrast.
I always use the standard cyanotype formula and also for these experiments solution (a) was prepared with 10 g ferric ammonium citrate in 50 ml water and solution (b) with 4 g potassium ferricyanide in 50 ml water. Furthermore, both the conventional and the alternative prints have been obtained with the same exposure time.
I believe this method is especially interesting for taking control of the development process, since the use of the brush allows one to apply the solution locally and with different dilutions. The cyanotype process works on the principle that ferric salts are reduced to ferrous salts when exposed to ultraviolet light so we can play with the potassium ferricyanide solution to form Prussian blue.
By the way, the Book of Photography considers the ferro-prussiate process "very unsuitable for general work" … because … "it gives white lines on a blue ground only" so, on the next page it describes Cyanotypes (?!) "to have a white ground and dark lines". The author actually describes the Pellet process that is also known as positive cyanotype!
Blueprint to cyanotypes – Exploring a historical alternative photographic process
by Malin Fabbri and Gary Fabbri
A well illustrated step-by-step guide to cyanotypes.
A lot more information on the process, chemicals, coating, exposure, printing, making negatives, washing and troubleshooting is available in this book.
Strongly recommended for beginners