Niepce invented a photomechanical process using a sensitised pewter plate. The images produced were called heliographs. Photogravure became the commercial process for reproduction in the late 19th Century.
Photopolymer film - UV light sensitive. Laminated onto any smooth surface.
Photo-intaglio - Image is held in the photopolymer surface.
Steps for Positive Image on Transparency for Photo-intaglio
Before preparing the image in photoshop to make a positive transparency, ensure that it has been saved at 300 dpi.
- Open image in Photoshop. Image>Mode>RGBColour>16Bits/Channel.
- Image>Mode>Grayscale, to remove colour.
- Clean and modify the image, i.e. Image>Adjustments>Levels or Brightness/Contrast. Resize to the dimensions you want the image printed.
Image>Image Size to set to 15x21cms for this example.
- Edit>Convert to Profile>Grey Gamma 2.2 (Windows) Grey Gamma 1.8 (Mac) to increase tonal range.
- Image>Adjustments>Levels or Curves to achieve best tonal range.
- Flatten image if necessary,Layers>Flatten and reconvert to 8-bitchannel, Image>Mode>8/Bits Channel before printing the transparency.
- Print, File>Print select CC_Upper_Art_Xerox@bramley
Image preparation from drawings
The following can be used to create images:
- ● Mark resist film. Can use pencil, acrylic, guache etc
- ● Photocopies on acetate
- ● Scanned images output as half tones onto film
Laminating the Plate with Photopolymer Film
Avoid handling the film in direct sunlight and have a light-safe folder/box for the plates. The Etching Room has red darkroom lights. The film has 3 layers, a photosensitive layer sandwiched between two clear plastic layers. Set plate on some newsprint. Cut film slightly bigger than the plate. The film curls back on itself. From the inside of the curl, peel away the clear layer and then stick to the plate. Take the plate to the press, cover with the blankets and turn the press.
Take plate and return to the darkroom, ensuring that the plates are light-safe, and trim the excess film of the plate with a scalpel. The return the plate to the light-safe box.
Exposing the Plate for Photo-intaglio
A test strip must be produced which will result in a more accurate way of establishing the correct exposure time.
Check the UV light unit has been switched on for at least five minutes to reach optimum strength.
If the image does not have a halftone screen then you must expose an Aquatint screen onto the surface of the photopolymer. This will produce the midtones of the image. Carefully place aquatint screen emulsion side up, place plate face down onto the screen and cover with newsprint/blanket to protect the rubber vacuum frame.
Close the frame and expose for 5 units.
5 units is a good average for an image with various tonal makeup.
Check the test strip to establish the optimum time then set the UV to that time, in units. Place the transparency, right-reading, onto the glass of the exposure unit. The emulsion side of the image should be in direct contact with the plate. Put the plate
face-down onto the image, cover with newsprint/blanket, clamp down, switch on vacuum and expose the plate.
Developing the Plate
Dissolve half a tablespoon of Sodium Carbonate (washing soda) in 2 litres of warm water. Remove the remaining plastic layer from the plate and place face up in the developer. Gently rub the surface of the plate with a sponge for 2-3 minutes.
Gently spray with vinegar to “Stop” the developer. Wash thoroughly and gently with cold water. Blot the plate, dry it quickly and thoroughly.
Post bake the plate or harden the plate under the UV for 3-4 units.
Printing the Plate
Clean the plate with a little vegetable oil to prevent the paper sticking to the plate.
Ink the plate with the edge of thick cardboard.
Form an inking pad from scrap net curtains and press and twist into the inked surface of the plate to remove the ink form the non-etched part of the plate.
We now plate the inked plates on the press with damp paper. The moisture of the paper will draw out the ink onto the paper.
The cloudiness is visible on the right on the printed image. Slightly disappointed.
The plate can now be cleaned with vegetable oil (red spray) and detergent (blue spray).
This was an interesting and enjoyable induction although I cannot see how this technique work with glass. Intaglio ink is very viscose and needs moist paper to draw out the ink from the etched part of the plate. However, for the purpose of creating prints and collages as part of the creative process, this has a lot of potential. A scan could be made of the finished prints or alternatively just using screen printing as a method will save a lot of time. I am looking at etching directly onto glass in the FabLab using the laser cutter/etcher.