Examples of Photogravure Prints
No image deterioration, very stable image
Slight Image Relief
Aquatint reticulation pattern
Common Use Dates: 1890-Present
Alternate Names: Dustgrain photogravure, Heliogravure, Gravure, Photo-aquatint, Photo-gravure, Talbot-Klíč photogravure
Mistaken For: Aquatint, Collotype
Process Family(s): Photomechanical, Dichromated Colloid, Paper Support, Intaglio, Print
Photogravure is a photomechanical process combining intaglio and photographic printing technologies – specifically aquatint and dichromated colloids, respectively. Photogravure prints are rendered in ink but possess fine detail and tonal gradations comparable to those found in true photographs. For this reason the process was often used to produce high quality reproductions of photographs and works of art.
The photographic quality of photogravure prints is the result of a microscopic reticulation pattern known as aquatint. Aquatint was developed by printmaker J. Van de Velde in 1650. The process was largely forgotten until the mid-18th century when it was refined by practitioners, most notably Paul Sandby who first coined the term “aquatint” for the medium’s ability to reproduce ink and color washes. Aquatint ground consists of rosin or powdered asphaltum (also referred to as bitumen) that is used to create a randomized texture pattern on the printing plate. These acid-resistant dust particles are melted onto a cleaned and degreased plate. They form tiny mounds around which acid bites during etching to yield ink-bearing pits.
In conjunction with aquatint, tonal gradation is achieved by using dichromated gelatin. In the photogravure process, gelatin acts as an etching resist regulating how deeply the acid bites into the copper plate. Upon exposure to light, dichromated gelatin hardens in proportion to the light received.
In 1852, William Fox Talbot patented a means of producing photographic engravings by coating steel plates with potassium dichromate in gelatin, then exposing the plate beneath a wax-paper positive to form an image in gelatin relief. He later improved the process by exposing the image through black crepe to break up continuous tone values into “halftones” for mechanical printing. In 1854 Charles Nègre published a similar process in La Lumière using etched steel to produce randomized grain halftones. By 1858 Talbot had developed a precursor to the photogravure by depositing resinous powder onto an exposed, gelatin sensitized copper plate. The plate was then heated, bonding the particles to the gelatin to create a finely grained etching resist.
Talbot’s process was refined by Karel Klíč in 1879 and has survived into the 21st century relatively unchanged. Klíč utilized carbon tissue--pigmented dichromated gelatin on a paper substrate--as the etching resist, eliminating the need to coat the plate with gelatin. He also applied resinous powder directly to the copper plate rather than to the gelatin, allowing deeper etching in the shadow regions and creating a very fine grain. Although several variations of photogravure were in practice at the time of his developments, Klíč’s process rapidly became predominant among them.
To produce a print using the Klíč process, a cleaned and polished copper plate is dusted with aquatint particles (rosin or asphaltum) using a specially designed dusting box or through several layers of cheesecloth. The plate is then heated to affix the dust particles. The carbon tissue resist must be sensitized in a cold bath of ammonium or potassium dichromate then adhered using a squeegee to a smooth drying surface (such as glass) to ensure flat and uniform drying. Once the resist has dried, it is exposed to UV light beneath a film or glass positive. Because gelatin hardens in proportion to the light it receives, highlight regions will harden more than shadow regions and mid-tones will partially harden. Prior to development, the resist tissue is dampened and adhered face down to the aquatinted plate. Development occurs in warm water; the gelatin in the shadow regions is washed away leaving a thin layer on the plate. In the highlight regions, where the gelatin most hardened, a thick layer remains. The tissue backing is peeled away in the bath leaving an image in gelatin relief on the plate. The plate is dried and etched in a series of ferric chloride baths of decreasing strength. The penetration speed of the acid is determined by the thickness of the resist while the use of multiple baths increases control over the etchant, ensuring subtle details and tonal gradations are properly rendered. When complete, the plate is rinsed in running water to stop etching and remove the gelatin and aquatint resists from the copper plate.
To print an image, stiff ink is rolled onto the plate, filling the pits etched around the aquatint. These pits are of varying depths and will deposit ink in various thicknesses thereby rendering a photographic tonal range. Excess ink is removed by manually wiping the plate and the remaining ink is transferred to paper in an intaglio press.