Finding Image Exposure Time - Basic

The work flow involves a double exposure technique for burning an image to the KM73 plate. Both the Base Exposure Time (“screen”) and the Image Exposure Time (“image”) must be found. Frequently, the times are the same. But, going through the extra steps of finding a separate Image Exposure Time will make sure that both times are correct and the highest quality plate is made.

3 Ways to Find Image Exposure Time

Parity

Assume that the time needed for image exposure is the same as the time needed for the initial aquatint exposure. This frequently works, but it does not provide much data for troubleshooting. Since it was presented in the previous section, the parity option will not be discussed here.

Basic

Find the Base Exposure time needed to make a good aquatint matrix. Use that time to make a good aquatint on a new plate, then make variable exposures of an image to that same plate.

The first part of this section will explore the basic option, using a home made contact frame and an old Aristo Platinum Printer. Here is how the experiment was set up:

Base Exposure Time of: 13 minutes

Image Exposure times of:

Base Exposure -1= 12 minutes
Base Exposure = 13 minutes
Base Exposure +1 = 14 minutes
Base Exposure +2 = 15 minutes

The notes I wrote on the back of the plate are:
Screen: 13’
Image: 12’, 13’, 14’, 15’
Fixxons transparency
Aristo Platinum Printer
Epson 3800

Advanced

This will be shown in the next section.
In short, it is an evolution of the Basic version, with the addition of a series of printed step wedges that provide more information.

Black and white photograph of the Grand Canyon showing towering rock formations, steep cliffs, and a river running through the canyon floor, with some vegetation in the foreground.

Notes on Nomenclature

“Base Exposure Time” is used to mean the same thing as “screen time”, which is just shorthand for “aquatint screen time” and “stochastic screen time” or simply “screen”.

“Image Exposure Time” is the same thing as “image time” or “transparency time”, or simply “image”.

It seems confusing. I am using these interchangeably to expose you to the varied nomenclature found in help forums, social media, and the writings of other artists. The important thing to remember is, regardless of the names, there are two distinct exposure steps: one to establish a dot pattern and another to create the image on top of that dot pattern.

Basic Option

Choose an image with enough tonal range to prive useful feedback. A digital step wedge will provide the most reliable information. Print that image with the same settings used for all other images.

The image in this example fits on an 8.5” x 11” piece of transparency. It will cover most of an A4 size KM73 plate.

A grayscale gradient chart displaying a smooth transition from black on the left to white on the right, with vertical columns labeled with percentage values from 0% to 100%.

Pull up the print screen and check all of the settings to make sure they are the same as any other transparency that will be printed. Consistency is important.

Print the transparency and let it fully dry. Go through the normal process of creating a good image transparency.

A computer screen displaying a photo editing software with a print dialog box open. The print preview shows a grayscale gradient from black to white with percentage labels at the top and bottom.

Place a polymer plate on the printing frame.
Place the transparency on top of the plate.
Make notes (on both the transparency and the print frame)
that will mark different exposure times for the experiment.

A grayscale chart demonstrating different levels of exposure. The chart shows 21 steps with varying shades of gray, from black to white, printed on transparency film using an inkjet printer. There are markings for different exposure times: 14 minutes, 13 minutes, 14 minutes, and 15 minutes, and labels indicating the corresponding exposure percentages at the top.

Remove the transparency.
Keep the polymer plate in place.
Place the stochastic screen on top of the polymer plate.
Expose the stochastic screen for the Base Exposure time.

(this example uses a Base Exposure time of 13 minutes)

Instructions for UV light exposure process with a sample polymer plate

Remove the stochastic screen and replace it with the image transparency. Line up the transparency with any registration marks you may have made on the contact frame.

Tape part of the transparency so it does not move.

Make the first exposure.

Grayscale grayscale tablet chart showing the effect of transparency on visibility at various exposures and printing times, with a scale at the top from 100% to 10% transparency and markers on the right indicating exposure durations from 13 to 15 minutes.

Cover the first section of the transparency, and make an additional expsoure of 1 minute to the parts that are still not covered by the light-blocking plastic.

Grayscale tablet with 21-step exposure chart printed on transparency film using inkjet printer, showing varying shades from black to white, with instructions on exposure time adjustments at the top.

Move the light-blocking plastic down one more space, and expose again for 1 minute.

A grayscale gradient chart illustrating exposure times for a 21-step grayscale tablet printed on transparency film with an inkjet printer, with instructions for moving the plastic down one zone and making a 1-minute exposure

Keep moving the plastic down one more spot, repeating this process until all parts have been exposed.

Grayscale step wedge chart with 21 shades from black to white, labeled with exposure times from 12 to 15 minutes. Instructions on creating and analyzing the exposure are above the chart, with red arrows pointing to the left and right sides. Text at the bottom states '21 step grayscale tablet printed on transparency film with inkjet printer.'

Write all important information on the steel side of the KM73 plate. The most important information is the range of exposure times used in the experiment:
both the Base Exposure Time
and the different Image Exposure Times.

Other important information can include date, brand of transparency film, inkjet printer setting, UV exposure type.

Person working on a lightbox with a diagram and a note indicating camera settings and date.

Place the plate on the contact frame.
Peel off the protective film.
Place the stochastic screen against the plate, making sure that the printed side of the screen faces the polymer side of the KM73 plate.

Person working on a wooden setup with a heat press machine, preparing materials with measurements and markings for printing or framing.

Expose the stochastic screen for the Base Exposure Time.

In this example, Base Exposure Time is 13 minutes.

A person operating a temperature control device connected to a heat press machine with stacks of paper on top.

After exposure, remove the stochastic screen.

Person flipping through a dark-colored book or folder on a table with sketching paper, a ruler, and a notebook nearby, all illuminated with orange lighting.

Put the image transparency (step wedge) on top of the polymer plate, making sure that the printed side of the transparency faces the polymer side of the plate.

Mark off four even spaces that indicate the planned image exposure times. Make marks on both the bed of the contact frame and on the plate itself. This redundancy can help if information is not successfully transferred to the plate or final print.

In this example, marks were made to delineate 12, 13, 14, 15 minutes.

Person measuring and marking a glass panel on a wooden board with gridlines for a project in a workshop

Make the first exposure to the entire image using the shortest time listed for the experiment.

In this example, the first exposure is 12 minutes.

A laboratory setup with a heat press, multiple clamps, and a control device displaying a temperature of 120°C, on a wooden table. A person's hands are adjusting the control device.

After the first exposure, remove the glass from the contact frame, but keep the image transparency against the KM73 plate (you taped one edge of it, right?).

Using a piece of thin opaque material, cover the part of the transparency and plate that was marked for the first exposure.

In this example, the opaque material is a piece of the light-proof shipping bag for the KM73 plates. The first exposure is 12 minutes, so that is the strip that is covered.

A person is working on a printing screen or screen printing frame with measurements marked on a wooden surface. The workspace is illuminated with orange lighting.

Expose the plate for enough additional time to make the second exposure.

Since the first exposure was made to the entire plate, additional exposure times are additive. Anything covered will not be exposed.

In this example, the exposure is for 1 minute.
12 minutes previous exposure.
One part covered.
1 minute additional exposure = everything uncovered will have 13’ minutes (total) exposure time.

Laboratory setting with a heat press and a control panel displaying '10.00'. Multiple items including scissors and a notebook are on the table.

Using the marks made on the contact frame as guides,
cover sections after they received enough exposure.

In this example, the plate was exposed for 1 minute after each time the plastic bag was moved:
12 minutes initial image exposure
covered a section, plus 1 minute exposure = 13’
covered a section, plus 1 minute exposure = 14’
covered a section, plus 1 minute exposure = 15’

Close-up of a person working on a framed piece of art, with measurement markings on the workspace, and red arrows pointing to specific areas.

When finished with all the exposure times, bring the plate to the washout tray. Let it sit, undisturbed for 1 minute. Gentry brush the surface for 1 minute…

Go through the usual drying, curing, inking, and printing process.

Person holding a sheet of black paper over a lightbox, with a cutting mat and other art supplies nearby.

Look closely at the results to find the best exposure time.

Look at both the plate and the resulting image.

Different zones on the image may look similar, but the plate will reveal inconsistencies in the aquatint matrix that might exist in different times.

Choose a time that has the best image and finest aquatint pattern. The intersection of these two things will give you the most range when you make a correction curve later.