By Lothar Osterburg ©
The technique I describe, teach and practise is the original 19th century Carl Klic / Fox Talbot photogravure process, utilizing a dustgrain aquatint.
In the last decade photogravure has had an enormous comeback and has enjoyed increasing popularity. An internet search will come up with dozens of results. Upon closer look however, the term photogravure describes a multitude of techniques. It starts with the fact that in latin languages (Italian, French etc.) photogravure is the word for photoetching in English - referring to a halftone, not continuous tone image. In German, French and Italian, the word for photogravure is heliogravure (sun gravure).
Recently the development of various new photographic polymers (Image-on; Solar plates...) has given rise to polymer photogravure techniques, frequently just called "photogravure". In most cases they only approximate a true continuous tone with the use of the fine halftone dots given by the newer generation inkjet printers. Technically those are still just photoetching processes. The true continuous polymer photogravure techniques use a continuous tone film positive in the making of the plate and an exposed aquatint screen. The latitude of values in these prints however seems greatly limited. The plates are soft polymer plastic, which can not be reworked, nor hold up to a larger edition without damage. I expect more new developments in this field in the future, which could make certain applications of photogravure easier without great loss, but doubt they will replace the traditional photogravure anytime soon.
Summary of the Process
A paper-backed gelatin is sensitized with a Potassium Dichromate solution and dried.
Penetration of the light through the film positive into the gelatin.
The resulting hardening of the gelatin. More exposure will harden the gelatin deeper.
The gelatin is adhered with water to a clean, polished copper plate:
Exposed gelatin adhered to a copper plate.
Development is done in warm water. The warm water dissolves all the unexposed, unhardened gelatin and releases the backing paper (the melting point of the exposed gelatin has increased under the influence of light). The remaining gelatin leaves a negative relief of the image on the plate and will act as the etching resist:
Developed gelatin resist on a copper plate.
A rosin dust grain is applied and melted onto the dried gelatin (other aquatint methods using asphaltum or a mezzotint screen are possible as well):
Aquatinted photogravure plate ready to be etched.
Water from a Ferric Chloride solution has to soften the layer of gelatin before the copper plate can start to etch. The amount of water in the solution controls the speed at which the gelatin breaks down, and with it the final contrast of the image. More water will soften the gelatin more rapidly. During this process the thinnest areas in the gelatin (the shadow areas) break down first and start to etch.
Plate during etch.
Plate etched to completion.
Once the plate has been etched to completion it is washed off and cleaned; the image is preserved and stable:
Etched photogravure plate.
Inked up photogravure plate.
The ink is transfered in an etching press to heavy printing paper that has been softened with water.