DK 3 photopolymer film – calibration of film, exposure unit and positives

The first time you want to make a photogravure, you have to calibrate your exposure unit. The procedure is the same with all photopolymer films (Imagon, Photec, Pureetch etc) and all UV-exposure units.

In the following I am using my own UV-exposure unit (distance between UV-bulb and vacuum frame 70 cm) equipped with the OSRAM ultra vitalux 300 watt UV- lamp, my own high-definition aquatint screen and the DK3 photopolymer film.

In principle you have three different positives (made on transparent drawing foil or film):

• The Aquatint Screen which you buy ready-made

• The continuous tone which can be a drawing, a Indian ink wash, a guache wash, an image (photo, text, anything) printed in black from the computer (300 ppi - resolution of at least 1440 dpi) on a normal inkjet or laser printer. The black must be 100%

• The halftone can be any image from the computer (photo, scanned washing etc.). It must be printed from the computer (300 ppi - resolution of at least 1440 dpi) in 70% black as a halftone (with error diffusion). Only professional printers are able to print halftones – if this is not possible on your computer, you have to make a continuous tone or get the halftone from a prepress bureau.

Calibration of the aquatint screen

1. Place the laminated copper plate on the vacuum frame.

2. Place the aquatint screen on top.

3. Switch on the vacuum, place a lightproof sheet on top and turn on the UV light. Move the lightproof plate a little every 15 seconds until you have pro­duced a photopolymer film with an exposure scale, ranging from 1-3 minutes (in this case) of the aquatint screen.

4. Take out the plate and place the exposed plate in the developer for 8 minutes with a lightproof lid on top op the tray.

5. After 7-8 minutes take away the lid. Use a sponge in the developer as though you were washing the plate very gently for 15 seconds or until the aquatint grains can be clearly felt.

6. Take the plate out of the developer. Rinse, harden, ink up and print the plate

Example:
In this case I started exposing the plate 1 min, 1.15, 1.30 etc up to 3 min.
As you can see the 2 min exposure is the first jet-black step and that will be my exposure for the aquatint screen in future.

Calibration of the Continuous Tone

1. Place the laminated copper plate on the vacuum frame.

2. The first time you expose the continuous tone positive it should also be calibrated the same way as the aquatint screen using a lightproof sheet.

3. Replace the continuous tone with the aquatint screen. Place the aquatint screen on top and expose it 2 min.

4. Take out the plate and place the exposed plate in the developer.

5. Use a sponge in the developer as though you were washing the plate. Develop the plate with steady movements all over the plate.

6. When it starts going coppery in the black areas (after about 15-30 sec) take the plate out of the developer, rinse it in running water, harden, ink up and print the plate.

Example:
Optimal exposure time is the time when you get most of the delicate grey tones as well as the deep blacks represented in the final and dry print:

Indian Ink Wash on drawing foil -  In this case I exposed the plate 30 sec, 45 sec, 1.00 min, 1.15 – optimal exposure 1.00 min

Photo from computer on ink-jet transparent - In this case I exposed the plate 5 sec, 10 sec, 15 sec up to 55 sec – Optimal exposure 20 seconds

Calibration of the Halftone

1. Place the laminated copper plate on the vacuum­frame.

2. Place the halftone on top. The first time you expose the halftone positive it should also be calibrated the same way as the aquatint screen using a lightproof sheet.

3. Take out the plate and place the exposed plate in the developer.

4. Use a sponge in the developer as though you were washing the plate. Develop the plate with steady movements all over the plate.

5. When it starts going coppery  in the black areas (after about 1 min) take the plate out of the developer, rinse it in running water, harden, ink up and print the plate.

Example:
Optimal exposure time is the time when you get most of the delicate grey tones as well as the deep blacks represented in the final and dry print :
Halftone on ink jet transparent printed on Epson Stylus Color 3000- In this case I started exposing the plate 5 sec, 10 sec, 15 sec up to 55 sec) – optimal exposure 20 sec

Further and more detailed descriptions of the process you will find in my book HANDBOOK OF NON-TOXIC INTAGLIO

Henrik Boegh / www.GrafiskEksperimentarium.dk