Photogravure (called heliogravure in Europe), blends photographic and etching processes to produce an original work of art with a textural richness, luminosity and range of tone not possible with conventional photographic printing processes. The painstakingly complex continuous tone process, called aquatint photogravure, dust-grain photogravure or Talbot-Klic process, works as follow:A negative image on film is converted in the desired proportions to a positive film. The positive film is placed in a vacuum contact frame and exposed by ultra-violet light onto a dichromate-sensitized gelatin carbon tissue. A fine dust of asphalt powder is laid and melted onto a highly polished copper plate. The exposed carbon tissue is then applied onto the grain-dusted plate and dried. The carbon tissue now adhering to the plate is developed in warm water, leaving on the plate various thickness of gelatin corresponding to the photographic information. After conditioning, the plate is etched in three to four baths of ferric chloride solutions of different concentrations which penetrate the different thickness of the gelatin accordingly, thus creating an etch of various depths. After etching, the plate retouched in traditional engraving techniques, is inked, hand-wiped and printed like an etching with an intaglio press onto a damped cotton fiber paper. The print is then dried and cured. The photogravure process is truly a lost art; the importance of the medium lies in the way it connects art and science, past and future, the ethereal and ephemeral qualities of light with the concreteness and permanence of ink on paper.
The Photogravure Technique:
A full-size positive image is developed on film from a traditional negative photographic image, or with pencils or inks on a sheet of Mylar. I often use a combination of both as I work with several layers of films for a single image. Densities are carefully recorded on a densitometer, the ideal range being between 0.3 for the highlights to 1.8 for the shadows.
A copper plate (I use 18 gauge) is cleaned, mirror polished, degreased with a 3% solution of sodium hydroxide in water, and deoxidized with a solution of 10% acetic acid, 200gm of salt in 1 liter of water. It is imperative that the plate be impeccably clean.
The Gelatin Tissue
A sheet of carbon tissue (a fine coat of gelatin laid on paper) is cut a little larger than the size of the plate. In the darkroom, the carbon tissue is sensitized to light in a solution of 3% potassium dichromate in distilled water, rolled face down and laid to dry as evenly as possible on a sheet of glass or Plexiglas, n order to produce a high gloss surface when dried.
The positive film is placed, right side up, emulsion side down, on top of the sensitized gelatin. The positive film and gelatin tissue are placed in a vacuum frame. The ultraviolet sensitive gelatin is exposed to ultraviolet light in an amount determined by the densities of the film and will become a permeable resist to the etchant (ferric chloride) when transferred onto the copper plate later. Once transferred to the copper plate, this gel will regulate the rate at which the ferric chloride seeps through to start etching the copper underneath. In line etching, the resist either blocks the etchant completely or admits it where incised.
A very fine asphaltum powder fused to a copperplate, or rosin fused to gelatin, or a photo image of the powder exposed to the gelatin, create minute "lands" which will remain unetched. Between these "lands", crevices are etched so that they will hold ink. Known as aquatint for its resemblance to the wash effects of watercolor, this technique greatly expanded the tonal range of etching when invented in the 18th century. Very fine asphaltum or rosin particles suspended in a box are allowed to rain down on the copper or gelatin in a random pattern. These particles are then fused to the plate or the gelatin over high heat until they melt lightly. The photographic acquatint, or photographic screen, is simply a positive photo of the powder exposed into the gelatin, after exposure of the image.
The exposed gelatin tissue is placed in a transfer solution of 20% alcohol, 80% distilled water. The tissue is lightly brushed and placed upside down onto the copper plate. It is then quickly and gently rolled onto the copper plate, avoiding any air pockets to be trapped. Adhering the ultraviolet-exposed gel to the copperplate in the dark is a very delicate operation, as the gel is both sticky and easily subject to damage when wet. It must be performed quickly, before the purified copperplate has a chance to oxidize. Should any defect be evident at this point, proceeding further would be futile as defects are always magnified in the next steps, etching and printing. After allowing the bond between the ultraviolet-exposed gel and copperplate to set for a while, usually about 10 minutes under a fan, the plate is immersed in a bath of water at exactly 110 degrees Fahrenheit for three minutes, the paper backing is gently removed, leaving only the gelatin on the copperplate. The next step is to wash the unexposed resist. This operation is performed in water at 100 degrees Fahrenheit, by rubbing very gently (barely touching) a cotton swab onto the gelatin while immersed, replacing the melted gelatin with clean water. Moisture is removed from the gelatin by the immersion of the plate in a solution of 50% to 80% of alcohol in distilled water for a few minutes, depending on the relative humidity of the studio. It is then left to dry and conditioned in the atmosphere of the studio, usually overnight. After retouching any possible minute defects in the gelatin, the plate must be masked back and front to confine the etching to the image area and is now ready to be etched.
To etch the plate, I prepare a series of ferric chloride baths (usually 5), ranging from 45-Baume to 39-Baume (a measure of concentration at 68 degrees Fahrenheit). The first etchant can penetrate only the thinnest resit, corresponding to the shadow areas of the image. A more dilute etchant, containing more water, soaks through the thicker resist and starts etching the mid-tones and highlights in succession. If the resist has been over-exposed, the etchant will never get through the highlights. A correctly exposed resist enables etching of all tones with full details. Ultraviolet-sensitive materials, unlike standard photographic films, respond in a linear way to the full range of light intensity, retaining tonal differentiation in the near-whites as well as in the shadow. Since etching generally speeds up as it progresses, etching of highlights at the end must be brief in order to retain the light tones. At the right moment, the etching is ended by immersing the copperplate in cold water. Depending on the coverage of dust in the aquatint and the exposure of the gelatin, the etch can range between 20 minutes to an hour. The resist and the acquatint having done their work, they now can be removed from the copperplate with a variety of strong chemicals.
A first proof can now be made to assess the condition of the plate and ink is prepared for that purpose. Etching ink must have the right tack or stickiness to transfer properly from copperplate to etching paper. A blend of finely ground pigment, cold-pressed linseed oil, various materials to promote or retard drying, and add transparency or opacity are mixed together. For suitable consistency, the ink should be slowly falling but not flowing off the knife. This condition, created by needing the ink many times with an ink knife, produces the most even wiping characteristics and the clearest impressions. The densities of black can be modified by mixing black ink with sepia, burnt umber, blue or red as best fit the image. Ink is applied to the warmed copperplate using a brayer, allowing it to settle into all the crevices. Further worked into the crevices using tarlatan (a cheesecloth-like material) in a circular motion, the ink is then wiped by gradually reducing the pressure, leaving more ink in the deeply etched shadows and less in the highlights. Each stroke of the tarlatan, however, drags some ink out of the shadows and spreads it over the highlights. This can be used to impact plate tone or reduce contrast in specific areas, while proceeding from light to dark areas of the image will enhance contrast. Finally, the white areas of the plate are wiped by hand with a fine powder of French chalk. Often, a final light stroke of clean tarlatan over the entire plate is applied to enhance the blacks. After cleaning the beveled edges, the plate is ready for the first proof.
Etching papers differ greatly in how they take ink, how absorbent they are, the amount of sizing they contain and their surface texture. They need enough strength to withstand great pressure and sufficient delicacy to register the finest nuances. Etching papers need to be soaked in water, in some cases for up to twenty-four hours, then dried on surface just before printing.
The etching press consists of a press bed held between two rollers which are adjusted to exert enough pressure to transfer ink from plate to paper. Three blankets of felt absorb the heavy pressure and push the ink into the wet paper.
After proofing, the copperplate is trimmed to final size, beveled, cleaned and retouched with burins, roulettes, burnishers or dry points if needed. The beveled edges which will leave a plate mark embossment distinctive of an etching must be completely smooth in order not to hold any ink during printing. If an edition of more than five or six prints is anticipated, the plate needs to be steel-faced. A fine coat of steel, applied by electrolysis will protect the plate from ware in inking and pressure from the press during printing. The plate is now ready for final printing. A decision is made regarding the size of the edition, in my case, I have printed editions ranging from five to one hundred prints. After drying, each print qualifying to be in the edition will be numbered, signed and embossed with the studio chop mark. Imperfect proofs will be destroyed and the copperplate cancelled so that further editions are not possible. Traditionally, an edition includes three to five artist proofs (AP), one reference print (BAT) and one or two printer’s proofs (PP). When a duo-tone effect is desired, the plate is printed in "chine-colle". In such case, a thin washi (Japanese paper) such as gampi can be combined with a heavier sheet of paper during printing, which will give an additional tonal effect and separate the image area from the whiteness of the paper. It is called chine-colle in reference to the Asian paper (once upon a time from China, now almost exclusively from Japan) glued onto the base paper. The gampi is cut the size of the image, an archival quality adhesive is applied, it is then carefully placed on the plate, the base paper is then placed on top of the gampi and rolled through the press. In my case, I often use this technique to apply color to distinct areas of the print, in a painterly manner.
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