Forget my last post where I said I would be doing cyanotypes. That's a story for another day.
I got distracted doing some initial work at home with photopolymer gravure, or polymer photogravure, or photopolymer etching. This is a process I really want to get my arms around. Let's start with some basics.
Photogravure is an intaglio process perfected in part by none other than William Fox Talbot - the inventor of the negative/positive photographic process. He is not to be confused with Lawrence Talbot. The Talbot-Klic process, as we know it today, was defined in 1878. Traditional photogravure employs a polished copper plate covered with a photo-resist that is chemically etched to create an intaglio plate for printing.
Photogravures can be beautiful. Paul Strand's Mexican Portfolio is considered an outstanding example of the art. Alfred Stieglitz published many beautiful photogravures in his seminal periodical Camera Work.
A new method for doing gravures is possible with photopolymer plates. Developed for the commercial printing industry, photopolymer plates are UV sensitive and harden when exposed. Placing an positive image (such as above) in front of the plate will produce a photographic relief on the plate. I will go into this in a bit more detail in a later post, but to get an image suitable for printing it is necessary to do a second exposure with an aquatint screen. The screen is essentially a random halftone pattern that eliminates "open bite" (large inked areas with no texture in the plate to hold the ink).
The plate I am playing with is the Toyobo Printight KM 73. The Toyobo site has a summary of the platemaking process. Add the second exposure with the aquatint screen and you have the polymer photogravure process.
One frustrating thing about alternative photography processes is the lack sometimes of critical information - such as the manufacturer's model number for a Toyobo plate when bought through a reseller. Toyobo makes many different types of plates for different uses. Note that none of the plates were developed specifically for photogravure. The best suited seems to be the Printight KM 73. A similar plate that can be used is the KM 43 - which has a thinner polymer film. A problem will arise if you start mixing plates up as the thicker the polymer, the longer the exposure required. Jon Lybrook suggests that the thicker plate allows for a deeper etch to hold more ink, giving richer blacks.
The plate has a clear protective film on the polymer which is removed prior to use. The unexposed plate shown above has a golden sheen. I'll talk more about preparing the plate later, but I want to note that I dust the plate with talcum powder which is mostly brushed off. The powder helps to eliminate air bubbles when you place the image emulsion side down on the photopolymer surface.
The plate to the left was exposed for 1 minute 30 seconds with the positive image. Note the appearance of some detail as the polymer changes color when cured by the UV light.
The plate was then exposed with the aquatint screen after redusting with talcum powder.
The plate is washed by brushing with a soft broad brush in water for two minutes, dried first with some blue lint-free shop towels, and then dried completely with a hair dryer on high heat.
This photopolymer process is also called non-toxic etching or non-toxic photoengraving. No chemicals are used to etch the plate - water is used to dissolve the unexposed polymer. This is a very safe process compared to traditional copper plate etching.
Once the plate is thoroughly dry, it is placed under the UV light source to fully cure the remaining polymer. The resulting plate is remarkably strong. In industrial applications these plates can easily print to the tens of thousands of images.
The final plate will look similar to the plate to the right.
While pretty rugged when cured, the plates should not be cleaned with water or alcohol which can damage them. Use low odor mineral spirits and baby oil instead.
On a humorous note, I would like to point out that the plate is reversed from where it should be. This plate prints out mirrored. A little mistake.
The plate texture looks very fine - Mark Nelson describes the surface as silvery.
The plate can hold a surprising amount of detail. The real question seems to be whether the process can produce images as detailed as that obtained from the traditional copper plate method. The consensus seems to be no - but the technology of polymer plates advances on.
Here is an enlargement of small text on the exposed plate. The numerals are highlights - raised relative to the darker (washed out during cleaning) background. The random pattern from the aquatint screen can be clearly seen in the area surrounding the numerals - providing the texture necessary to hold the ink in the black areas for printing.
I wanted to post some initial notes on the process. Jon Lybrook's notes are comprehensive and gave me a great head start on the entire process.
In future installments I'll go into more detail on plate preparation, problems and solutions.
And eventually I'll return to the cyanotype discussion. Did I mention we entered the rainy season here in California? This threw a wrench into my plans for describing how to expose cyanotypes using the sun as a UV source. I suppose it just emphasizes that if you get very far into some of these processes, you will likely be unable to avoid purchasing a UV lightbox.