Photogravure

As photogravure (from the Greek helios = sun), also Helio engraving, photoengraving, photo gravure, photogravure, photogravure, Klicotypie or solar pressure called, refers to a photographic precious printing process. The photogravure is the precursor of modern art gravure printing, can be reproduced by a photo- mechanical printing process with photos and illustrations, and can be displayed with the true halftones. It is a further development of the aquatint process. Thus, the pressure required for this plate is prepared similarly as for the aquatint etching.

History

The photogravure was invented in 1879 by Karl Klietsch ( = Karel Klic ).

" Invented in 1884 [ ... Johann Baptist Obernetter ] a new method of photogravure, which granted the benefit of a real facsimile reproduction without retouching. "

Techniques of the photogravure

We distinguish direct copy and pigment paper copy.

Direct Copy

A copper plate is dusted with rosin or asphalt and powder is melted by heating the grid. Moreover, a gelatin layer is applied. This is sensitized by bathing in a potassium or ammonium dichromate solution ( made ​​sensitive to light ).

After exposure by way of contact copy by a semitone slide the development takes place in warm water. The chrome gelatin hardens by exposure, while the unexposed parts remain washable. This creates a gelatin relief. Depending on the strength of relief, the acid can penetrate the gelatin. A thin layer allows rapid penetration of which the copper is etched longer time and thus gets deeper screen cavities ( = darker tone), with a thick layer can not or only belatedly penetrate to the plate the acid, whereby the latter is hardly or not etched. During etching, thus produces differently deep recesses that can accommodate different according to the gelatin relief much color after washing the gelatin layer and allow differentiated Halbtonwiedergaben.

Pigment paper copy

Wherein the pigment to paper copy of the templates to a photosensitive, treated with potassium or ammonium dichromate chromium gelatin paper, the so-called pigment paper, exposed as original large slide in the contact process. The paper is softened after exposure a few minutes in cold water and applied to a copper or steel plate that has been prepared in Aquatintaverfahren, pressed ( clapped ). To develop the paper and the unexposed portions of the gelatin layer can be detached and washed away in warm water. It remains a delicate gelatin relief on the plate. The artist can control and manipulate the subsequent etching in ferric chloride bath. Often (III) chloride solutions will etched Mehrbadverfahren with several different concentrations of iron, as the FeCl3 the tanned gelatin layer varies depending on the concentration and diffuses at different speeds to be etched on the copper plate. By so controlled different etching times and the rasterization by the aquatint the plate can print halftones.

Use

Today, the Photogravure is an industrial pressure no longer in use, but lives in the artistic gravure on. However, it is used in the sense of craftsmanship to the preservation of old graphic by reprints.

Hazard Statement

Ammonium dichromate and potassium dichromate are toxic and carcinogenic chemicals