Monday, June 22, 2009

Cyanotype: An historical practice still in use.

Cyanotypes are not just a piece of history. In fact people are still using this very simple alternative process to make some beautiful photographs. By people I am referring to photographers around the world, and me included. I have just ordered my first cyanotype kit from Hunts Photo and Video. I am anxiously awaiting the kit to come in so I can start working on a few prints that I have been waiting to print and exhibit. I also have a few surprises for this new process. So, now that you know that cyanotypes are no longer a thing of the past, you might be asking, ok, well what the heck is a cyanotype. Cyanotypes are a photographic printing process that gives a cyan-blue print.

There are a few reasons why I am going to experiment using the cyanotype kit. 1. I was recently asked what I knew about cyanotypes. I knew a few things about them, for example, the history of cyanotypes and what they were used for. But, I have never made any cyanotype prints. So, this leads to number 2.  I have a few surprises that I am working on and a few other images that I am going to set up as a limited addition for an up and coming exhibition this summer. I plan on scanning them so I can feature the prints here. I hope that the images will inspire some of you to look outside the box and try something new, get your hands wet, or blue for that matter.  Below is a more concise look at what cyanotypes are and how to make them.

The English scientist and astronomer Sir John Herschel discovered this procedure in 1842. Even though John Herschel is perhaps the inventor of the cyanotype process, Anna Atkins actually brought this to 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 female photographer.

The process uses two chemicals:

They result in a photo-sensitive solution when dissolved in water, which is used to coat a material (usually paper). A positive image can be produced by exposing it to a source of ultraviolet light (such as sunlight) with a negative. The UV light reduces the iron(III) to iron(II). This is followed by a complex reaction of the iron(II) complex with ferricyanide. The result is an insoluble, blue dye (ferric ferrocyanide) known as Prussian blue.

The developing of the picture takes place by flushing it with flowing water. The water-soluble iron(III) salts are washed away, while the non-water-soluble Prussian blue remains in the paper. This is what gives the picture its typical blue color. The process was popular in engineering circles well into the 20th century. The simple and low-cost process enabled them to produce large-scale copies of their work, referred to as blueprints.

In a typical procedure, equal volumes of an 8% (w/v) solution of potassium ferricyanide and a 20% solution of ferric ammonium citrate are mixed. This mildly photosensitive solution is then applied to a receptive surface (such as paper) and allowed to dry in a dark place. Cyanotypes can be printed on any surface capable of soaking up the iron solution. Although watercolor paper is a preferred medium, cotton, wool and even gelatin sizing on nonporous surfaces have been used. Care should be taken to avoid alkaline-buffered papers which will cause degradation of the image over time.

Upon exposure to ultraviolet light (such as that in sunlight), the iron in the exposed areas will reduce, turning the paper a steel-grey-blue color. The extent of color change is dependent on the amount of UV light, but acceptable results are usually obtained after 10-20 minute exposures on a bright, sunny day. The highlight values should appear overexposed as the water wash will reduce the final print values. Prints can be made with large format negatives and lithography film, or everyday objects can be used to make photograms.

After exposure, the yellow, unreacted iron solution is rinsed off with running water. Although the blue color darkens upon drying, the effect can be accelerated by soaking the print in a 6% (v/v) solution of 3% (household) hydrogen peroxide.

The overall contrast of the sensitizer solution can be increased with the addition of 1% (w/v) solution potassium dichromate. Approximately 6 drops for every 2ml of sensitizer solution.

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