WHAT IS A PHOTOGRAVURE?
and other Photo Intaglio Definitions
The goal of this page is to educate people (including artists, teachers, students, curators, collectors and dealers) to the main differences in the various types of photo intaglio printing processes. It is my hope that people will use the appropriate term when describing the processes or medium of these prints. The public already knows too little about these processes so it is important that they are not further confused or misled when looking at prints or learning a process. These simple terms serve to quickly and efficiently describe exactly how a photo intaglio plate and print was made. Correct terms with alternates are in bold for each category.
Fine Art Photo Intaglio Processes
Photogravure (see photogravure plates in the photo below)
Photogravure is a process of etching continuous tones into copper with a sensitized gelatin pigment paper resist (aka carbon tissue) using a continuous tone positive and aquatint screen or dustgrain aquatint. The process was invented by William H. F. Talbot and Karl Klic in the late 1800s for archivally reproducing fine photographic prints. They employed the use of the bitumen dustgrain aquatint for its high resolution organic grain as well as its ability for deeply etched shadows. The dichromate sensitized gravure gelatin has a straight line UV sensitivity response which makes it the most capable of reproducing the sublest range of tones and detail in the continuous tone film positive. The tones of the positive are imparted inversely to the exposed gelatin which is adhered and developed on the copper. The dried gelatin which is varied in thickness acts as an etch resist. The etch begins in the shadows followed by lighter shadows, the midtones and lastly the highlight tones, all etching in proportionate depth to their respective densities. This continually self staged resist yields an etched plate that will print with a varying depth layer of ink. Careful timing of the different etching baths also adds another way of controlling the tonal curves and maximizing the tonal range of the image. The gravure process yields an etched plate that can be retouched and re-worked with any of the traditional etching processes. The copper plate is often electroplated with iron (steel faced) for printing very consistent and/or long editions. Photogravure is also referred to as 'Gravure' or 'Heliogravure'. When a drawing on mylar or vellum is used instead of a photgraphic positive the print is known as a 'Direct Gravure'.
Photo Etching is a process where a metal plate, usually copper or zinc, is coated with a high contrast, negative working photo-sensitive resist such as KPR or sensitized fish glue or a thin film photopolymer such as Puretch. The photo resist is exposed to a very fine halftone positive or high contrast line image. A halfone creates an illusion of tone by using tiny black dots of varying size and distance. Halftones are made digitally now with inkjet or laser printers. If an aquatint is required for any large areas of solid black it can be done traditionally with dustgrain or spray, with a separate screen exposure or built in digitally. The plate is developed with a solvent or mild alkaline producing a high resolution etch resist. This process yields a plate that can be etched to the desired depth and tone. In photo etching all of the exposed plate and dots will receive the same amount of etch unless manually staged out by the artist. The photo resist is usually stripped before printing and the etched plate can be retouched and re-worked afterwards with any of the traditional etching processes. Some artists are using gelatin pigment paper (see Photogravure above) for exposure and etching of fine halftones. Because of the nature of etching a halftoned image, these prints should be called 'photo etchings' and not 'photogravures'. A Photo-Etching can also correctly be labeled as simply 'Etching'.
Photopolymer intaglio is a non-etch process of making a photo intaglio printing matrix. Plates are either manually coated with a thick photopolymer film (Imagon) or they are available as pre-coated plates such as Solarplate and Toyobo flexographic plates etc. Plates laminated with film are typically exposed with a very fine halftone positive that has a grain built into the blacks. Pre-coated plates can be exposed with the halftone method or with a continuous tone positive which requires a separate exposure to an aquatint screen. The plates are developed in water or a mild alkaline solution which washes away the unhardened photopolymer creating fine recessed crevices for the ink. The photopolymer film and plates adapted here for fine art intaglio printing were designed for high contrast exposure response and print applications. Therefore the photopolymer emulsion is inherently not as sensitive to the full range of tones that photogravure gelatin resist was created specifically to reproduce. 'Photopolymer Intaglio' is also correctly known as 'Photopolymer'. These descriptions can also be used when positives are hand drawn on mylar. The 'Photopolymer Intaglio' process is often incorrectly referred to as 'Photogravure', 'Photopolymer Gravure' or 'Polymer Gravure'. The inclusion of the word gravure here is misleading since there is no etching or engraving involved, there is only developing.
A print made with any of the processes above could be called Photo Intaglio or simply Intaglio but when the description is more specific then the term should accurately reflect the process used.
Some Related Commercial Printing Processes
Etched rotogravure is very similar to photogravure except a line screen is always used for the grain and the image is etched onto a metal cylinder using the same gelatin pigment paper resist. Now in the US and Europe most rotogravure cylinders are made with computer controlled diamonds or lasers that engrave the various depth cells. Rotogravure is the first commercial printing process to become 100% digital. Chemically etched rotogravure is still going strong in other parts of the world. Rotogravure is used where high quality reproduction and/or long run printing is required. National Geographic is printed with rotogravure.
Photo engraving is used in circuit board manufacture, chemical milling of parts, metal relief plates for printing and foil stamping or embossing dies. Pre coated zinc, magnesium or brass plates are used for high volume relief print runs and embossing. Photopolymer films and liquid resists are used to coat these plates.
Flexography is a commercial relief printing process that uses a pre-coated flexible photopolymer plate. Varying thicknesses and durometers are available. These plates have been adapted for Photopolymer Intaglio as well as hand printed letterpress. Flexography is a form of rotary web letterpress using flexible photopolymer image carriers and fast-drying inks fed from an anilox inking system. Flexography is the major process used to print packaging materials. The plates are exposed with a halftone negative of about 175 dpi.
Pad Printing is an ofseet intaglio printing process used for printing small 3-D surfaces and parts. An intaglio plate is made of the artwork and a soft silicone pad presses into the inked recesses and picks up the ink which is transferred to the objects. Steel plates are used for long run print jobs and photopolymer plates are used for shorter run jobs. Golf balls, pens and computer keys are just a few of the items printed this way.
©2011-2014 Cape Fear Press
Below: Photogravure plates made in the July 2011 gravure workshop