6. Aquatint Screen Exposure test
Aquatint Screens are available from ImagOn distributors. (see intaglio materials Polymetaal internet shop)
Before using an Aquatint Screen a step exposure test should be done to determine the best Aquatint Screen exposure for your exposure unit:
When determining the optimum test exposure for the Aquatint Screen for the first time it is good to be cognizant of the following points: If the Aquatint Screen has not received enough exposure the light source you are using will not have penetrated the Aquatint Screen structure thus hardening the ImagOn emulsion on the plate. If you look at the Aquatint Screen under a magnifier you will notice a random black dot structure with clear space between the dots. It is the clear spaces where the UV exposure light needs to penetrate the Aquatint Screen. UV light exposure hardens the ImagOn emulsion. Thus if not enough light gets through these spaces then most of the ImagOn emulsion will wash off the plate creating an UNDER EXPOSURE or whatlooks like open-biting.
If too much light penetrates these clear spaces then the light burns under each black dot of the Aquatint Screen and OVER EXPOSES the ImagOn plate. Both under and over exposed Aquatinted areas look grayed out with the major difference being the amount of ImagOn emulsion being exposed. In the first instance not enough is being exposed and in the second too much is being exposed. The correct exposure lies some where these two extreme exposures.
Once the Aquatint Screen exposure has been established, for your particular exposure unit, it should stay stable (effected only by the fall off of light due to aging exposure system bulbs) The next exposure issue will be your Image Exposure. Whether your image is a wash-drawing, photocopy, inkjet print or direct drawing onto the top Mylar of the ImagOn plate you will need to make exposure tests to determine which is the best exposure for each media type.
The golden rule with Intaglio-Type IMAGE exposure is; THE SHORTER THE EXPOSURE THE DARKER THE RESULTING IMAGE AND THE LONGER THE EXPOSURE THE LIGHTER WILL BE THE PRINTED IMAGE.