In the jargon of engravers it is known as aquatint positive screen by analogy with the chalcographic technique, where random dots of resin are arranged on metal plates, accommodating the base for the construction of tonal images through the action of the mordant. In photogravure with a polymer plate, the aquatint screen is exposed on the polymer plates prior to the analog or digital positive.
The aquatint screen is essential to structure the polymer plate and achieve the reproduction of continuous tone images (with tonal scaling). Whether working with positives of autographic origin or with positives of digital origin, the use of a stochastic screen is necessary. The stochastic raster is composed of randomly arranged microscopic dots that make it possible to print images with tonal gradations. The stochastic plot helps us to take advantage of all those grays that would not appear otherwise. In summary, a stochastic aquatint screen is essential to avoid open bites and losses in tone scales.
The Rittagraf team has created 3 different types of aquatint screens. The three differ in the size of the plot point.
- Chunky Knit Weft: 84 micron size dot
- Medium Dot Screen: 40 micron size dot
- Fine Dot Screen: 31 micron size dot
Rittagraf frames have been worked and tested for polymer photo-engraving. This does not mean that it cannot be used in another technique, but tests should be done.
The screen greatly affects the final quality of our photopolymer plate. The tonal range that we can achieve in photogravure printing depends on the structure and arrangement of the plot. To learn more about the use and of this type of pattern on photopolymer plates, we recommend Ramón Freire's book: The graphic act as construction. Autographic positive and photopolymer plate (spanish language). Among others, we also recommend you: Polymer Photogravure, A new Method for Photographers and Graphic Artists, from Taneli Eskola and Kari Holopainen.