Blueprint – making photosensitive paper
Blueprint or cyanotype is an old photographic technique that was mainly used for making copies of large technical drawings and plans. When you talk about a blueprint in everyday life, you usually mean a plan for something. With the advent of the photocopier and other inexpensive reproduction techniques, the blueprint disappeared. Fortunately, there are always people who are interested in these ancient techniques, purely out of curiosity or because of their artistic possibilities.
You can make blueprints on paper, textiles, basically anything that you can wet with water. The substances to be used are not very dangerous. The procedures of sensitization and development are simple: for example, the exposure time is neither very short nor very long and you do not need expensive equipment. The disadvantage may be that it always produces a blue/white or (after coloring) gray/white print.
Blueprint – making photosensitive paper – takes two steps:
- making the solutions
- make it photosensitive
Making the solutions
You make the photosensitive layer by first making two solutions and then mixing them in equal parts. From the moment you mix the solutions, the solution is photosensitive. You then apply this photosensitive solution to the substrate. The most suitable is paper that can absorb a lot of water and will not tear, for example watercolour paper, or textiles, preferably cotton or linen.
The two solutions have the following composition:
- 10 g Potassium ferricyanide red
- 100 ml fresh tap water
The Potassium ferricyanide red (T) dissolves quite easily in the water without heating.
- 30 g Ammonium iron (III) citrate 
- 100 ml fresh tap water
Ammonium iron (III) citrate dissolves a little less easily, but good stirring is usually sufficient.
Ordinary fresh tap water can be used as water, or, if possible, demineralized water from the supermarket or drug store. The salts to be dissolved can be ordered from De Hekserij. The above recipes are not very precise, it is no problem if a little more or less is solved, feel free to experiment with this. When making textiles photosensitive, a higher concentration is recommended.
Prepare the solutions in a beaker or measuring cup and transfer to bottles for storage. Store both solutions separately in dark glass or PET bottles. No jars with metal lids: iron, tin and steel can have a negative effect on the solutions. Solution II can start to mold, that’s not a disaster, but remove the mold before use.
The solutions are in general green-yellow in colour. The mixture of both can also be dark green or blue. This is due to the formation of Prussian Blue in the solution. This can lead to differences in the end result.
Making it photosensitive
The sensitization should be done in a place with low ultraviolet light, indoors in a not too sunny area is usually fine. Blinds or curtains are closed and every kitchen, every classroom and certainly every darkroom is suitable.
Mix an equal volume of both solutions, for example 10 ml of both. Apply this new solution to the paper or fabric to be photosensitive. You can do this with a sponge, cloth, brush, whatever you want. However, do not use brushes or other items with metal parts, these can adversely affect the process. Then allow the photosensitive material to dry. This should preferably be done in a dark room, for example in the attic, or in a closet. When it is dry it can be used. It can be used wet, but it is more likely to run through and the sensitivity is less. The sensitized paper is yellow-green to blue in colour.