I’ve been working on some new print designs that use atmospheric effects and interesting skies. To make these prints, I need to be able to make smooth color gradients where I can change hue, saturation, and value across the page. Today I did some experiments with two-color gradients.

Each of these two-color gradients was made by printing a single gradient plate two times in with different colors and orientations. The effect works pretty well with lighter colors, but I notice that the gradient does not appear as smooth with the darker colors.

The experiment involved a 4″ x 5″ photopolymer plate with a linear gradient running from full ink at the top to clean plate at the bottom. My process was to print the plate in a light color, then rotate the plate 180 degrees and print it again in a dark color. The goal was to get a smooth transition from the dark color to the light color.

After printing so much black and white, it was refreshing to see all the colors. The prints were attractive and I was pleased to see that I could make a blue to yellow gradient without getting green in the middle.

My main problem was that my gradients weren’t very smooth. They look as if the plate is somehow mottled or even scratched. I have a number of theories but it will take some experiments to sort things out.

Here are the leading contenders

• Over-wiping the plate
• Non-uniform wiping
• Color inks require a different wiping technique than black ink
• Ink consistency
• Not enough printing pressure
• Plate got damaged during development
• Poor contact between plate and aquatint screen during exposure
• Poor contact between plate and positive during exposure

My plans are to print the plate with a known good black ink, on the small press where I am more familiar. I will use a lot of printing pressure. If I still see the problem, I will print a known good plate to verify that the problem isn’t with the press and ink.

Then, depending on the results, I may make a second gradient plate and see whether it shows the same problems.

After completing the Precision Digital Negatives process calibration, I was finally ready to make my first photopolymer gravure prints! For this initial round, I chose two designs – one using solid black and solid white and the other using the full value scale. The plates were 4″ x 5″ SolarPlate, exposed first with an aquatint screen and then again with a positive which was printed onto Pictorico OHP.

This photopolymer gravure plate contains no gray scales – it only has solid black and solid white.

I liked this design a lot, but was a bit underwhelmed by the print. It doesn’t know whether it wants to be photograph or a graphic. The idea still has potential so I’ll take it back to the drawing board. I think I will go with simplification over photo realism.

This plate is from a photograph of an ice covered pond in Boston. The plate uses the full range of gray values, calibrated with Precision Digital Negatives.

The print came out really well, especially given that it is from my first round of photopolymer gravure prints, using Precision Digital Negatives for the first time, and using the Glen Alps press for the first time.

I finally got a chance to use the Glen Alps Press for the first time. It has been over a month since the press arrived, but before I could make prints I needed to get new felt blankets and level and adjust the press. Today I made my first print on the press – it was a 3″ x 5″ photopolymer gravure plate.

I chose this photopolymer gravure plate for the press inaguration.

The giant press makes the 4″ x 5″ plate look miniscule.

Here’s the big reveal of my first print on the Glen Alps press.

Musicians practice scales before concertos. As an art student I practiced value scales in vine charcoal before attempting to render a sphere. Now in the printmaking domain, I am doing the same thing, only this time I am working with Mark Nelson‘s Precision Digital Negative (PDN) process to calibrate my photopolymer platemaking and printing process.

No matter how you do it, process calibration involves lots of test strips.

The goal is to develop a repeatable, end-to-end process starting from the creation of the original artwork, to exposing and developing the plate, through the final printing step. There are many variables that impact contrast, texture, the range of values, the richness of the blacks and the purity of the whites. I want to be able to control each of these variables in order to make the print that I see in my mind’s eye.

The PDN system is a general process for calibrating the production of digital negatives and positives for alternative photographic processes that use ultraviolet light to expose the final image. Mark has put a huge amount of effort into developing and refining the PDN system. His e-book is excellent and chock full of details and explanations of the process itself and related topics like image acquisition and preparation and Photoshop tips. The e-book also comes with membership to a PDN discussion forum where you can get answers to most questions. If you are making digital negatives or positives, I highly recommend purchasing the PDN book.

Creating photopolymer plates for intaglio requires exposure to a positive, rather than a negative. I print my positives onto a transparency film called Pictorico OHP, using an Epson Stylus Pro 3880. I use two types of plates – ready-made SolarPlate and plates I make by laminating ImageOn film to sheets of acrylic. I expose the plates using an old Nuarc 26-1K platemaker that I picked up on Craig’s List.

I’m most of the way through calibrating my SolarPlate process. Once I have the SolarPlate process refined and stabilized, I will repeat the calibration for the more complex ImageOn process.

At a high level, the PDN calibration process involves 4 steps:

1. Determine the correct exposure time for clear film.
2. Determine the mixture of ink colors in the transparency that yields the ideal density range for exposing the plates.
3. Generate a gradient scale using the ideal color mixture
4. Generate a set of Photoshop level adjustment curves that linearize the gradient scale.

The photos below document my journey through the initial SolarPlate calibration.

The first step is to determine the correct exposure for clear Pictorico OHP film. One could do this by experimenting with a bunch of different exposure times, but it is much quicker to make a single exposure through a step wedge that incorporates a variety of calibrated neutral densities which simulate shorter exposure times.

Here’s the step wedge plate, inked, wiped and ready to print. The darker portions of the wedge correspond to darker regions on the plate. Each step in the wedge corresponds to 1/3 f-stop.

When exposing positives for photopolymer plates, it is important to choose an exposure that just hardens the plate so that it prints pure white in areas where the film is clear. The exposure for this test strip is spot on, but it is apparent that I have a contrast problem because the plate goes from white to black in about four f-stops.

It turns out that black inkjet pigment is not well suited to producing fine tonal gradations in most alternative photographic processes. The problem is the black is just too strong and the printer can’t generate enough different gray values in the narrow range required by the photopolymer plates. Imagine trying to render a figure with a Sharpie and you get the idea. Mark’s insight is that one can choose a mixture of much weaker color inks in order to produce a positive with densities that match the response curves of the plates. By using color inks, it is possible to create hundreds of distinct values across the entire range from white to black. This is a huge improvement over black inks which are so dense they can only create a handful of distinct values in the densities useful for plate making. The squares in the test strip above represent about 150 different color mixtures. The goal is to choose the mixture that just barely yields black.

Here’s the color test strip, printed on white paper. Each of the gray boxes corresponds to a different color mixture in the inkjet positive. I chose the forth box from the left in the row labeled B=255 + R=0-255. This box corresponds to a the RGB color R=30, G=0, B=255. This color mixture just barely manages to give me black when it is at maximum intensity. Lighter versions of this color give me lighter shades of gray.

Here’s the plate for the initial gradient scale. This plate was created from a positive that used a mixture of red and blue ink, instead of black. Each square on this plate is a different shade of the RGB color R=30, G=0, B=255.

Here’s the initial gradient scale, inked, wiped, and ready to print. Already it is apparent that the plate has a contrast problem – most of the plate is very close to either black or white – only a tiny portion in the middle shows distinct gray levels.

This is the initial gradient scale, printed on white paper and showing 100 different levels from white to black. This scale is not very linear – it is quite flat in the whites, then shoots up quickly to the dark grays and then flattens out again in the blacks.

This plate was created from a new positive which combined the original gradient with the PDN process adjustment curves. The process adjustment curves should linearize the gradient.

As you can see here, the linearized gradient plate looks much smoother.

This gradient was produced by applying Photoshop process adjustment curves to the original gradient. This curve is much closer to linear.