Cyanotypes - Super Easy Photo Prints at Home.

The goal of this instructable is to explain the cyanotype process. Cyanotype is a super easy (and cheap) photo printing process that you can do at home with a few special materials. Digital pictures printed as cyanotypes make great gifts.

Some history, from wikipedia :

Cyanotype is an old monochrome photographic printing process which gives a cyan-blue print.

The English scientist and astronomer Sir John Herschel discovered this procedure in 1842. Though Herschel is perhaps the inventor of the cyanotype process, it was Anna Atkins, a British scientist, who brought the process into the realm of photography. She created a limited series of cyanotype books that documented ferns and other plant life. By using this process, Anna Atkins is regarded as the first woman photographer.

Process Overview
1. Mix two chemicals to create photo sensitive solution of 'sensitizer'.
2. Brush, smear, or soak the sensitizer into cotton-based watercolor paper.
3. Create a negative image on a transperency with a laser/inkjet printer or copy machine.
4. Place the negative over the dried, sensitized paper.
5. Expose to UV light.
6. Wash the image in water to develop.
7. Hang to dry, and enjoy!

Step 1: Chemistry

Cyanotype requires a simple 2 part 'sensitizer' that is sprayed, brushed, or smeared onto a high-cotton content paper.

Safety
The cyanotype is perhaps the safest photo printing method. Still, basic safety measures should be observed. Cover your work surface, don't use any utensils that will be used for food, and wear safety gear. In the picture below I'm decked out in safety glasses, a DIY style face mask, and heavy rubber kitchen gloves.

The basic formula (from here):
100 ml water and 25g green ferric ammonium citrate is mixed together.
100 ml water and 10g potassium ferricyanide is mixed in a separate container.
The two solutions are then mixed in equal parts.

What I did:
I could not find the required chemicals in the Netherlands. My cheapest option was to buy from the Photographer's Formulary in the US (even with international shipping).
http://www.photoformulary.com
FAC 100 grams
PF 100 grams

Most tutorials suggests making 100ml of each solution. I didn't want to store these liquids so I made a much smaller batch. I chose to make 5ml of each solution, to be mixed for 10ml total sensitizer.

I do not have a scale, so I estimated the volume of each chemical I needed based on the overall size of the bottles (100g). I mixed a very rough 0.5g PF and 1.2g FAC each to 5ml de-mineralized water (used for clothing irons, car batteries, etc. Sold in bottles in the Netherlands for ~50 cents). These were mixed individually and then combined, as per the instructions above.

Step 2: Paper

A cyanotype can be printed on almost any paper, cloth, or even tile. I used 100% cotton water-color paper from an art paper store. It was not fancy (about 2 euro for a huge sheet), nor thick (~170 lbs?). Some people are more careful about paper selection. For other's views, check out the Alternative Photography forum here .

Brush, spray, or soak the sensitizer into the paper.

Leave the paper to dry, or speed it up with a hairdryer set to low.

Step 3: Negative

The cyanotype process is a negative photo process. Black on the negative becomes white in the final print.

I loaded my digital pictures into photoshop. Removed the color information (for a B&W image). Did image->invert for the negative.

The negative can be printed on an inkjet, laser printer, or copy machine. I printed my negative using an inkjet printer with inkjet transparency sheets. I used "high quality black and white" mode (which uses the color inks to make B&W). I did this because the colors are more UV-resistant than the black (in my experience, I make positives for doing UV/foto printed circuit boards that need very high accuracy).

The negative was placed with the ink against the paper. This is the same thing I do for PCBs - it really helps prevent unwanted light leakage.

The paper and negative were placed in a cheap picture frame to keep everything flat and aligned.

Step 4: Exposure

The print is put under UV light until the exposed sensitizer turns from yellow-green to 'confederate grey'. The sun or a UV tanning lamp can be used as a UV source. See the The Big Cyanotype Exposure Survey for more information on exposure times and techniques.

What I did:
The frame with paper & negative was placed directly under a home tanning lap set face-down on a table. This is exactly the same setup I use to make PCBs, albeit with positives and photosensitive copper-clad fiberglass board.

I did a number of exposure tests. First I tried recommendations from the survey, 15 minutes and 10 minutes. These were way over exposed. Next I tried 5, 3, 2.5, 2, 1.28 (the exact time I use for PCBs), and 1 minute. I settled on 1 minute and 45 seconds.

Step 5: Developing

First, wash the print in demineralized (distilled) water until all the yellow areas of unexposed sensitizer are washed out of the paper.

Next, rinse it in the sink (under running water) for a few minutes.

This can be your final step - hang the image to dry.

If you are impatient (like me), dip the print into a solution of 125ml (.5 cups) water with one cap full hydrogen peroxide to finish the development instantly. Without this treatment, the image will change to its final color over a few hours (as it dries). Note: at first I made a new solution each time, but then I used the same solution for 10 or so prints without a decrease in potency. Rinse the print again to clean it of any remaining hydrogen peroxide. Hang to dry.

Step 6: Other Stuff

I tried toning and bleaching on a few of the 'rejects'.

Toning
I simply steeped a bag of tea in hot water from the tap for a few minutes. I tossed the tea and print into a shallow container. It soaked for 5-10 minutes. The color is somewhat 'Diesel' denim or brown/black, depending on the observer.

Bleaching
I also did a bleach test. I mixed a heap of baking soda (naturium bicarbonate) in some warm tap water. This bleached the image clean off the paper in a matter of seconds. I know it works, but I have not tried to tune or control the process.

Improvements
My UV source is too close to the paper. Rather than getting over developed spots, I get light-ish underdeveloped bars where the reflector doesn't adequately distribute the UV light. This will probably be fixed by raising the UV light a few inches over the paper (of course this will throw off my exposure times...)

Conclusion
I'm really really pleased with my results. My images were not washed off by the Amsterdam tap water (my initial concern). A total lack of precision chemistry didn't hamper my ability to get great prints.