A description of the intaglio photogravure printmaking (made from etched copperplates) process by Peter Miller.
Always be careful when handling chemicals. Read the health and safety instructions.
- Prepare Positive Transparency
- Sensitize Resist
- Expose Resist
- Adhere Exposed Resist to Copperplate
- Develop Resist
- Etch Copperplate
- Pull a Proof
- Print the Edition
- Chine CollÈ Printing
Intaglio prints, made from etched copperplates, are one of three basic types of hand-made prints. They are immediately distinguishable from the other two types by their platemark, resulting from the pressure of drawing the ink out of the recess of the plate and into the paper. Like photogravure, the other intaglio techniques — engraving, drypoint, etching, aquatint, and mezzotint — require an etching press.
In contrast to intaglio, when the ink is below the surface of the plate, relief plates carry the ink and the design above their surface. These include woodblock and linoleum prints. The third basic type is called planographic, where the ink is on the plate surface, as with lithgraphs and silk-screens.
In a gravure print (also known as photogravure, hèliogravure, or gravure ‡ l’aquatinte), the tones and variations in light and shadow, and the textures of various surfaces, are the distinguishing features. Under magnification, the aquatint grain of a photogravure prints is visible. The gravure printmaking technique I use is based on the inventions of W H F Talbot and Nicèphore Niépce in the 1830s. The history of this technique and its relation to printmaking in Europe is sketched in my Inklings essay. This page and the two following describe in detail how to make photogravure etchings. These directions are based on my own experience, and at each step of the way there are many variations that will give equally fine results. The best way to learn is by experiment.
I. Prepare Positive Transparency
- From a well-exposed photographic negative, make a transparency on graphic arts film. Enlarge or contact-print to the size of the intended final image. Develop the graphic arts film in any standard film developer. Digital positives on specially coated transparency materials may be substituted for film. As of late 2004 or early 2005, we reached the crossover point where film and digital media are of equal quality. The new digital SLRs with larger light sensors combined with printers using pigmented ink (??) and fine-grained transparency materials are now more than adequate for photogravure. Many of the newer images shown on this website were made using digital transparencies.
- If a densitometer is available, develop the graphic-arts film or print the transparency material so that there is a density range of at least 1.5, for example a highlight density of 0.2 and a shadow density of 1.7. (Density is a numerical expression of opacity, on a scale of zero to three, of how much of the light is blocked.)
- Remove dust spots and any distracting highlights. This is done physically with film and by with a noise filter in a digital image.
- Mask the film transparency with red lithographers’ tape to create a ‘safe edge’ about 15 mm wide around the image area. Press the tape down from the center outward so that there are no creases or air bubbles. If using digital positive transparencies, print a black border around the image area instead of using lithographers’ tape. From this point on, the technique is the same for film or digital transparencies.
II. Sensitize Resist (‘Carbon Tissue’)
- From carbon tissue supplied in 100-meter rolls, place weights on unrolled end and cut to size, making sure the gelatin coating does not crack.
- Using cotton or synthetic gloves when handling the carbon tissue, cut pieces that are 1 ~ 2 cm larger than the transparency and 1-2 cm smaller in all dimensions than the copperplate.
- Store flat between stiff boards, the cut sheets of unsensitized carbon tissue that will not be used immediately. Secure with clips, wrap in foil or some other vapor barrier, and store it in the refrigerator if possible. Unsensitized carbon tissue can be stored this way for up to two years.
- Under an amber safelight, mix the sensitizer and pour it into a tray which is used only for this purpose.
- With rubber gloves on (see safety recommendations for the sensitizer), place a cut sheet of the resist face up in the tray, noting the time. Hold the corners and edges down until it is fully immersed and lies flat (about one minute).
- Pick up the carbon tissue by one corner and turn it face down, sliding it smoothly into the tray.
- After 3.5 minutes have elapsed since first immersing the carbon tissue in the sensitizer solution, pick up the resist by one corner and let it drip onto a piece of clean plexiglass.
- Holding two diagonally opposite corners, first set the center of the sensitized resist face down on the plexiglass, then set the corners down so that no air is trapped between the surfaces.
- Squeegee from the center outward with sufficient pressure to remove excess sensitizer and adhere the resist to the plexiglass, but not so hard as to weaken or distort the delicate gelatin.
- Dry the sensitized resist evenly by directing the air current from a fan over (not onto) the back of the resist. After about two hours (more if humidity is high), gently peel the sensitized carbon tissue off the plexiglass, making sure the surface does not crack.
III. Expose the Resist
- Handle the sensitized resist only with cotton or synthetic gloves. Use an amber safelight.
- Test UV exposure with step wedges (transparencies with a series of known densities) to indicate the proper exposure for a given UV light source. The test procedure is the same as the procedure for an actual transparency as described below. The exact time of ultraviolet exposure depends on the spectrum, intensity, and distance of each light source from the resist surface.
- Adjust UV exposure as needed for aging of the carbon tissue, density of the transparency, sensitizer concentration, the order in which the resist has been soaked in sensitizer, and whether a light-toned or dark-toned gravure print is desired.
- Position the masked transparency over the sensitized resist in the vacuum frame, taking care that the entire image area is covered.
- If a screen is used as aquatint grain, expose the screen 1.5X the image exposure, to ensure that the ‘lands’ of the plate will be more prominent than the brightest highlights of the image.
- If an aquatint grain is used, expose the transparency only.
Ultraviolet light (UV) sets off a chemical reaction known as cross-linking or polymerization that hardens or crystallizes the gelatin. When exposed in contact with a transparency (Figure 1), the shadows block most of the ultraviolet (UV) light, leaving most of the gel soluble. Under the transparency’s highlights which admit more UV, however, the gel hardens more. Metal-halide light sources give more consistent results and are safer to use than carbon-arc lamps.
The aquatint grain creates microscopic ‘lands’ on the copperplate which remain unetched. Particles of asphaltum are allowed to rain down on the copperplate and are then fused over high heat until they flow into an amoeba-like shape, as shown enlarged in Figure 1.
The unique look of photogravure depends on the variable depth of the etching, the ability of the copperplate to transfer far more ink to the shadows than to the highlights of the print, and to register subtle gradation of tone. What enables the plate to be etched to various depths is the linear sensitivity of dichromated gelatin to ultraviolet light. Unlike conventional silver-based photographic materials, dichromated gelatin is sensitive to every nuance of light intensity in equal measure. This enables it to register highlight and shadow detail not found in conventional photographs. The gelatin resist is partially permeable: It allows the etchant to seep through depending on how thick or thin the gel is. Where the gel is thin, etching is deep, and where thick the etching is shallow. The deeply etched parts of the plate hold more ink and form the dark parts of the gravure print, the lightly etched parts less ink, creating the highlights.
Molecules of gelatin activated by UV light bind to one another in long chains through a mechanism known as cross-linking (Figure 3). Cross-linking makes the resist more or less insoluble depending on how far it extends through the gelatin. The amount of cross-linking, remarkably, tracks the amount of UV precisely, even at the extremes of light and darkness. While ordinary photographic films and papers miss the near-whites and near-blacks because of their uneven sensitivity, UV-sensitive materials register the finest gradations of tone faithfully.
IV. Adhere Exposed Resist to Copperplate
- Remove any scratches from copperplate by scraping and burnishing with plate oil.
- Polish copperplate with metal polish.
- De-grease copperplate with fresh sodium hydroxide solution, followed by a fresh acetic acid / salt solution, wiping each time with a clean rag.
- Dry copperplate quickly so that there is no tarnishing, and place it conveniently to hand.
- Soak exposed resist in distilled water for 1.5 minutes.
- Immerse the clean copperplate in 27∞ C. distilled water.
- Quickly adhere one edge of the exposed resist to the copperplate, pull both out of the warm water, and squeegee the resist from the center outward until it is firmly adhered to the copperplate, making sure no air is trapped between the two surfaces.
- Remove excess liquid from the back of the adhered resist, and let dry (‘cure’) under pressure for two hours.
V. Develop the Resist
Immerse the plate in warm (27∞ C.) water, gradually increasing the temperature to 41∞ C. until the backing sheet is loose enough to peel off without dislodging the resist.
- Peel off backing sheet slowly.
- Agitate plate gently in 41∞ C. water for about five minutes until all the unexposed resist is washed off. The 15-mm ‘safe edge’ prevents the edge of the image area of the patterned resist from washing away.
- While the copperplate with the now-patterned resist is still immersed, cool the water gradually by adding cold water; then remove the copperplate and place it in a tray with a 50% alcohol / 50% water solution for 30 seconds.
- Remove the plate from the alcohol / water solution, hold it vertically, and immediately rotate it while drying the edges with a paper towel or rag. Do not allow water to flow back onto the image area. Keep rotating the plate and drying the edges for 10 or 15 minutes.
- Set the plate in a vertical position, and rotate it 90 degrees every 15 minutes for one or two hours, to prevent uneven drying of the resist.
- With a 10X or 15X loupe, inspect the plate for flaws such as bubbles, blisters, under-exposure, over-exposure, resist breaks, mottling, poor adhesion, etc. Unless flaws appear easy to correct after etching the plate, scrub off the patterned resist and start over.
- If the inspection shows a well-modulated range of tones so that both shadows and highlights can be etched while retaining full detail, and there are few or no flaws in the patterned resist, let it dry in a dust-free room for about 15 to 20 hours.
The dried resist looks like a laterally reversed negative (Figure 4), light in the shadows (where the resist is thin) and dark in the highlights (where the resist is thick). It is actually a cast of the image that shapes the action of the etchant in the next step. To prepare the plate for etching, mask the image area and the back of the plate with packaging tape. The print made from this plate is Hokokuji, showing a bamboo garden in Kamakura.
Figure 5 shows an enlarged cross-section of the copperplate ready for etching, with aquatint grain or screen pattern below the permeable gelatin resist. A random-pattern screen m ay be used instead of the aquatint grain to create unetched ‘lands’ on the plate.
VI. Etch the Copperplate
- Mask the image area of the patterned resist on the copperplate with packaging tape, and apply stopout to any breaks in the resist. Where the tape meets at the corners, smooth it down so that no etchant can get through.
- Prepare a series of ferric chloride solutions ranging from 45-BaumÈ to 37-BaumÈ (a measure of concentration) at 20∞ C. (68∞ F.). Dilute the solutions, usually supplied as 45-BaumÈ, with distilled water, allowing time for the water and ferric chloride to mix. Pour the etchant into four or five trays arranged from most to least concentrated.
- Place the positive transparency where it is visible, and identify the darkest areas, midtones, and highlights, in order to follow the progress of the etching.
- Wearing rubber gloves and alab apron, immerse the copperplate in the most concentrated (highest BaumÈ) solution of ferric chloride and note the starting time.
- Move the plate to the next, more dilute solutions in sequence, watching for etching to begin. Etching begins when the ferric chloride seeps through the resist and touches copper, causing a flow of dark precipitate. Note the time when this shadow etching begins. Typically shadow etching begins after five to 15 minutes.
- If no new areas of the plate are being penetrated, move the plate to the next, more dilute solution to start midtone etching, and note the time when that begins.
- Try to pace the etching so that the shadows etch for at least 10 minutes, preferably 15 minutes, while the brightest highlights etch for two minutes or less, with the total etching time between 20 and 30 minutes.
- Let the highlights etch only briefly in the most dilute solution of ferric chloride. If the resist was over-exposed enough to slow highlight penetration, try breathing on the plate; the moisture in the breath helps the etchant to get through stubborn resists.
- End the etch by immersing the plate in cold water and moving it around to remove all the etchant.
- Scrub off the resist and aquatint grain (if any), and clean the plate with alternating baths of sodium hydroxide (NaOH, a strong base) and a solution of acetic acid mixed with salt.
- Inspect for etching flaws with a 10X or 15X loupe.
Figure 6 shows in enlarged cross-section how some parts of the plate are etched much more deeply than others.
VII. Pull a Proof
Ink, wipe, and print the etched copperplate in accordance with the printing instructions below.
- See whether the proof has good highlight and shadow detail, plate tone, depth, and whether it looks like your visualization of the image. If so,
- Cut the plate to the size of the image, with or without a border as desired.
- File and bevel the edges of the
copperplate, so that they will not hold ink.
Here is the etched copperplate from which the Hokokuji print was made.
VIII. Print the Edition
The day before you plan to print, prepare a stack of the etching paper you will use, alternating wet with dry sheets, wrap them in plastic, and place a flat weight on top. Use distilled or buffered water.
- The etching paper or washi should be damp and soft, but should not have any water visible on its surface.
- Adjust the pressure of the etching press so that it makes an even impression.
- Polish etched copperplate, and, using rubber gloves, de-grease plate with sodium hydroxide solution, and brighten it with acetic acid / salt solution. Dry plate quickly to avoid tarnishing.
- Mix black or sepia etching ink either from dry pigment together with cold-pressed linseed oil, or from prepared inks, kneading it repeatedly with a stiff ink knife until it has the desired tack or consistency. The ink should fall slowly off the knife, rather than flowing (Figure 6).
- Spread ink on clean copperplate
with brayer, covering the whole plate evenly.
Etching papers (Figure 7) differ in how they take the ink, how absorbent they are, in tone, and in surface texture. Contrary to what one might think, the inked copperplate actually prints quite faithfully onto a rough-textured paper, giving a pleasing contrast between the image area and the texture of the margin.
- Using circular motions of an ink-charged tarlatan (Figure 8), work etching ink thoroughly into all the crevices of the etched copperplate. Rotate the plate occasionally to change the angle of wiping.
- Clear ink from the plate gradually with long sweeping strokes of the inky tarlatan from edge to center.
- When an outline of the image is visible, change to a partially inked tarlatan and reduce the pressure of wiping. Concentrate on the shadows and midtones.
- When the shadows and midtones become more defined, adjust the direction of wiping so that it goes from highlights to darker tones. (Otherwise, ink will be dragged from the more deeply etched areas, the shadows, onto the highlights.)
- Using a clean tarlatan with very light pressure, continue clearing ink from the highlights, changing frequently to a clean area of the tarlatan.
- Examine the plate in raking reflected light, and if plate oil or wiping marks are visible on the surface, remove them with very light short strokes of a clean tarlatan, and if necessary with a fine rag or the side of the hand lightly dusted with whiting.
- Remove ink from beveled edge, border
(if any), and back of plate.
Some workshops strive for
uniformity across the entire edition, while others prefer some variety of
interpretation. The ultimate in uniformity is a
poster or other reproduction made without any particular individual touch or
- Measure dimensions of plate and paper, and divide the differences in half to position the plate to be printed in the center of the paper.
- Place the copperplate on the press bed, and use two rulers to define the margins corresponding to the measurements made in the previous step. For example, if the plate is 21 x 26 cm, the etching paper 28 x 38 cm, set the vertical margin at half of 28 – 21 cm, or 3.5 cm, and set the at half of 38 – 28 cm, or 5 cm.
- Place the etching paper or washi, front downward, on top of the inked plate so that the edges of the paper correspond to the margins set in the previous step.
- Place the etching felts over the paper, set press pressure, and rotate the press without stopping during the transit of the plate through the press.
- Draw back the felts and gently peel
the etching paper off the plate ~ voil‡! ~ the first
IX. Chine Collè Printing
- Ink and wipe the plate as described above in ß VIII. But wipe the plate more thoroughly, because in this type of printing the papers absorb more ink.
- Cut a piece of ganpi to the exact size of the etched copperplate to be used for printing.
- Immerse the inked plate in a tray of water (the ink and water won’t mix).
- Position the ganpi front side down on the inked copperplate and remove plate carefully from water while keeping the ganpi positioned correctly.
- Let the ganpi dry partially, then brush on wheat paste from the center outward to the edges.
- Again let the ganpi dry partially, using a fan if necessary.
- Place plate and ganpi on press bed, set margins as before, and place heavier sheet of etching paper over the ganpi.
- Print as above in ß VIII. The ganpi is adhered to the heavier etching paper and printed at the same time.
- Peel the print off very carefully, so that the ganpi stays adhered to the heavier etching paper.
The etching press creates a platemark (Figure 9), a distinguishing feature of gravure prints and of all intaglio prints. The platemark embossment is a sign of hand-made authenticity.
Sodium hydroxide copperplate de-greasing solution
|Water||800 ml||1500 ml||4000 ml|
|Sodium hydroxide||20 gr||40 gr||100 gr|
|To make working solution||1 liter||2 liters||5 liters|
USE RUBBER GLOVES AND WEAR PROTECTIVE GOGGLES. Mix carefully, a small amount at a time, stirring until thoroughly dissolved before adding more. If too much sodium hydroxide is poured in at one time, the solution heats up rapidly and may bubble over or splatter. Do not allow skin contact. This solution removes grease from the copperplate surface, which is essential for proper adhesion of the resist. Clean thoroughly and vigorously with a rag, using fresh solution as many times as necessary. When water flows off the plate in sheets and does not form droplets on the surface, the de-greasing is complete.
Acetic acid and salt brightening solution (ingredients by size=4 > volume)
|Water||800 ml||1500 ml||4000 ml|
|Acetic acid (glacial)||100 ml||200 ml||500 ml|
|Salt||100 ml||200 ml||500 ml|
|To make working solution||1 liter||2 liters||5 liters|
USE RUBBER GLOVES, HAVE VENT ON OR OPEN
WINDOW, AND WEAR PROTECTIVE GOGGLES. ALWAYS POUR ACID INTO WATER, NOT WATER INTO
ACID. DO NOT BREATHE ACETIC ACID FUMES. Quickly clean copperplate using a clean
rag with this solution, rinse plate, and dry it quickly by patting with a paper
towel to prevent oxidation. This solution forms mild hydrochloric acid, which
lightly etches the plate surface, so the operation must be performed quickly.
Flowing alcohol over the plate accelerates drying.
Sensitizer for Resist
|Water||800 ml||1500 ml||4000 ml|
|Potassium dichromate||35 gr||70 gr||175 gr|
|Ammonia||1 ml||2 ml||5 ml|
|To make working solution||1 liter||2 liters||5 liters|
USE RUBBER GLOVES, HAVE VENT ON, WEAR PROTECTIVE GOGGLES. POTASSIUM DICHROMATE IS EXTREMELY TOXIC BY SKIN CONTACT. DO NOT BREATHE AMMONIA FUMES. SEE SAFETY PRECAUTIONS. Under an amber safelight, mix potassium dichromate powder into water slowly, stirring continuously until completely dissolved. If possible, use distilled water. A dehumidifier provides a free source of distilled water. Add ammonia to alkalize the sensitizer solution. If the sensitizer solution is acidic, oxidation of the copper surface may occur during adhesion of the resist, interfering with adhesion. This table indicates a 3.5 percent solution. For more contrast with lower sensitivity, use a 3.0 percent solution. For less contrast with higher sensitivity, use a 4.0 percent solution.
Copper Plate Photogravure – Demystifying the Process
Step-by-step basic printing procedures for a photogravure plate, complete with trouble shooting information.
Printmaking in the Sun
Covering the solarprint, or the photopolymer process, an inspiring read!
The Complete Printmaker
Step by step through the history and techniques of over forty-five print-making methods.