What is etching? Etching is a type of printing that along side engraving comes under the category of Intaglio. Images printed (etchings) by this process are the results of ink being forced out of the incised lines etched in a zinc or copper plate employing a heavy press. This leads to slightly raised ink on the paper and a characteristic plate mark showing the sides of the plate.
History of Etching
The techniques of etching and engraving are believed to have originated in Medieval times as a means of decorating armour and metal. The incised lines would have often been filled to darken them and from this it would have been a short step to transferring the image to cloth or paper. One suggestion is knights falling on soft ground would have left an impression of the patterns on their armour.
Etching differs from engraving mainly in that acid does the work of removing the metal. This allows a fluidity of mark and in the hands of an expert a almost infinite degree of control; The depth of each line can be controlled by the acid and so can hold as much or as little ink as is required to achieve the desired tone. Most metals can be used for the etching plate although the most common are Zinc and copper. Zinc is often used as a starter metal for students as it is relatively cheap and easy to work. Copper is much denser and less brittle and will yield more prints. It can also be steel-faced to last almost indefinitely.
The two etching techniques I employ are Hard Ground (the most basic form of etching) and Soft Ground. I rarely use aquatint. The techniques I describe here are traditional methods adapted and modified to a modern domestic environment. Virtually everything apart from the printing can be done at home with suitable care and little space. The modern table top press is now capable of printing etchings that match those done on heavy studio press (at least for small plates) and so there is now no reason why even the printing cannot be done at home!
Preparing the etching plate
I use 16 gauge copper plate (1/16th inch) which comes in 500 mm x 1000 mm sheets polished on one side and covered with a plastic protective sheet. This I cut up (very carefully!) by scoring into it over 50 times with a heavy craft knife and then snapping it away. This may sound a little brutal but I have not had a lot of luck with guillotined plates – however sharp the blade there nearly always seems to be a slight bending or compression of the metal which is almost impossible to straighten and which causes the prints to fade away at that edge. Most of us don’t have a heavy duty guillotine lying around the house and trusting this to others can result in scratches and plates that vary in size and are not perfectly square. I have experimented with three plate colour etchings in the past and this can make the plates difficult to register. Before removing the plastic coating I roughly bevel the edges of the plate to a 45′ angle using a coarse file. This is optional but I find it much easier to roll the plate – with less chance of the roller catching the edge. When the print is finally ready to edition I finish off this bevelling with fine sandpaper and polish it up with the back of a spoon which gives a sharp clean print mark that does not cut the paper. Bevelling the plate before printing is compulsory in any class I teach! I have seen too many expensive blankets sliced through by the edge of an un bevelled plate
Copper sheets from printmaking suppliers include a protective sheet covering the polished front surface. This is not to be confused with zinc Jetplate which features a tough acid resistant coating on the back. I would advise keeping this on as long as possible (regard it just like the protective plastic they place on mobile phones or new laptops/TVs). After removing the plastic coating I clean the adhesive residue off with white spirit and check for scratches. If the copper plate has tarnished I polish it with Brasso.
Before laying the wax ground on I degrease the plate. Traditionally this would mean using a paste made from ammonia and chalk. For a domestic situation a mixture of soap powder and soda crystals dissolved in hot water works as a substitute. Be careful to dissolve the powder and crystals thoroughly first and use a soft sponge to wipe the plate. Cream cleaners like Jif (Now unfortunately renamed Cif!) used to be perfect as they contained ammonia but in our health and safety conscious times this has been changed and unfortunately they just don’t work satisfactorily. Recently I have discovered that Mr Muscle Kitchen cleaner is an admirable degreaser!
For heating the plate i take advantage of a standard domestic cooker (Gas is best, but with a touch of practice an electrical ring works almost as well. Manoeuvre the plate with a metal spatula so it’s heated evenly and place it on a flat smooth heat resistant surface (this will accumulate a build up of solidifying wax up so check it can be cleaned with white spirit!)
Hard and soft ground
In etching, the plate is first covered by a wax ground. It is this “resist” which protects the plate from the acid. Removing this covering with a needle will expose the underlying plate surface to the acid. Mistakes can be corrected by painting over with “Stop out” varnish. This is a liquid version of the wax ground. Ground usually comes in the form of a wax ball which is melted onto the heated plate and then spread evenly and thinly with a roller. The Ground can either be hard – for fine, precise lines or soft. With soft ground the wax doesn’t set; any textured object pressed into it will pull the wax off when removed, exposing the plate. Placing paper over soft ground and drawing on it will create marks similar to a hard pencil.
APPLYING THE GROUND
The wax ground melts onto the heated plate and is then rolled as evenly and as thinly as possible across the surface of the plate. I the wax starts sticking to the roller the plate can be reheated ,taking care to stop if the wax starts smoking as this will burn the ground and allow the acid through.
Hard Ground; Smoking the plate
This only applies to hard ground. Smoking darkens the wax ground to a black finish by letting it absorb carbon from a bundle of burning tapers. It isn’t strictly necessary and many people simply go with the plain ground. The lines can however be difficult to see as the plain ground is a rich honey colour against the bare copper of the drawn marks. Unfortunately the mistake many people make to counter this is to make the ground too thick, which causes it to chip and make for rougher lines.
Smoking involves clamping the plate on one edge with a pair of swan necked adjustable pliers (protect the surface of the plate with a small piece of folded card) and holding it above your head with the grounded surface facing down. This should be done before the plate has cooled entirely. Gently smoke the ground with a burning bundle of tapers
(about 10 bound spirally from the bottom with masking tape) so that the carbon softens the wax and is absorbed into it. Start further away from the plate and as the ground starts appearing shiny brush the tip of the flame (about an inch above the visible flame) across the plate in a systematic pattern. This will take a bit of practice but the plate should cool to a uniform semi mat finish. I harden the wax at this point by running it under a cold tap. Any powdery carbon on the surface can be gently rubbed away with an orange polishing duster.
Watchbell Street, Rye
Smoked Hard ground plate with drawn marks clearly visible., The varnished over (stopped out) patch where clamp was applied to hold the plate upside down for smoking, can be seen just down from the top right corner
Examine carefully for any specks of copper showing through as THESE WILL BE BITTEN! The surface can now be drawn on using a variety of instruments. I have used an old dart with a pencil screwed into the barrel and presently use a sewing needle threaded through a propelling pencil instead of leads!
END OF THE LINE
St Pancras station clock tower rises above washing hanging out to dry on washing lines strung across the courtyard of Midhope House on the Hillview estate in Kings Cross in the 1980s. One of a series of large (12 inch x 16 inch -big for an etching) copper plate etchings created in the late 1980s – 1990s.
The image was first sketched out using soft ground and the re-grounded and bitten in 8 stages starting with the darkest shadows (3 hour bite in total) to the lightest highlights (8 min) Each bite was half the duration of the last. The ground was only removed once.
What is etching? – the actual etching part of the process
When the plate is immersed into acid* the exposed areas are bitten and when the wax is removed the drawn image is revealed as having been “etched” into the plate. The plate can then be inked up with ink being driven into the etched lines. The plate is then wiped in order to remove the ink from the surface. A sheet of dampened paper is placed over the inked plate and both are rolled through a press under high pressure The rolling action and the pressure cause the ink to be squeezed out and sucked out on to the paper. The resulting etchings are characterised by extremely fine lines and subtle tones.
Successive biting to different depths can be precisely controlled with experience to create an infinite number of tonal variations.
*I use Dutch mordant: which is composed as follows: Hydrochloric, 200 grammes; chlorate of potash, 20 grammes; water, 880 grammes. This acid works slowly and evenly without undercutting the lines and without losing its strength as it bites. Nitric acid is more vigorous, but can cause deep lines to merge
Soft Ground Etching
A copper plate is covered thinly with soft-ground; a non drying wax which is resistant to acid. Any textured object pressed onto the wax will pull the wax off when removed and leave an approximation of its texture. Placing paper over the plate and drawing on it will therefore create textures echoing pencil marks and some degree of “shading” can be achieved. The plate can then be immersed in acid and bitten and then printed.
Biting the drawn copper plate in acid and incising the lines is essentially what differentiates etching from other printmaking processes and gives it its name!
ACID – DIFFERENT TYPES ACID FOR USE ON COPPER PLATE
The scariest part of etching is undoubtedly the acid! Endless films featuring bubbling, steaming bottles and beakers brandished by babbling mad scientists has given acid a bad image. YES! it is dangerous and should definitely be handled with care, especially at the mixing stage. NEVER add water to acid to dilute it – it will heat rapidly, probably spit and possibly explode. ALWAYS dilute acid by adding it slowly to cold water and ALWAYS in a well ventilated room with running water at hand in case of spills.
Nitric acid, which when diluted 1 part acid to 7 parts water gives a perfectly adequate bath for either copper or zinc ( do not use for both as the fumes can be dangerous) is a fast working solution, ideal for beginners, classes and experimental work. It bites vigorously and aggressively and can quickly lose its potency. It also tends to undercut and move sideways making close fine lines and hatching difficult to bite deeply. It tires quickly and timing can be difficult.
Dutch Mordant is an ideal mixture for Copper and can be used for zinc. It bites evenly and slowly, straight down and is very controllable. It slowly turns a bright turquoise with successive use and this can be accurately used to gauge its age and therefore strength.
Ferric Chloride is also used for copper. This bizarre solution is, I believe, more of a salt than an acid (I’m actually not too hot on the chemistry of all this!). Looking suspiciously like Worcester sauce it corrodes the plate, leaving a sediment which can impede its action on fine lines unless the plate is suspended upside down in the solution. It will stain anything it comes in contact with a rusty yellow and a few unnoticed spills can reduce anything metal to a crumbly biscuit texture in a frighteningly short time (I have lost a metal bath this way!)
ACID BITING TIMES
This is the area where the experience bit kicks in. How long should you leave a plate in the acid? The only real way of finding out whether a plate has been properly bitten is actually to clean it off and print it! I have seen many students ruin days of elaborate drawing by removing the plates too early and discovering their etching is a mere spidery faint ghost of what they wanted, or too late and finding that the subtly rendered tones they were hoping for have merged into one muddy, turgid black mess. Over-biting a plate will not just simply make it darker; in some cases fine, close hatching will merge and the resulting open area will have no texture to hold the ink – resulting in pale dusty looking “bald” areas with hard black edges.
If this happens then one solution is to reground the plate and then re-hatch the area that is too dark – biting it again but to only half of the previous bite. The fragility of the resulting texture means that the area can be burnished to a fairly light grey and subsequently redrawn.
HARD AND SOFT GROUND BITING TIMES
1 Initial sketch with simple tones
SOFT GROUND, Dutch Mordant on Copper
30 minutes and remove ground
2 Secondary drawing with shadows and more detailed mid tones :
SOFT GROUND, Dutch Mordant on Copper –
1 hour and remove ground
Apply coating of hard ground, smoke and do not remove between bites.
HARD GROUND Stages
Dutch Mordant on Copper working from darkest black downwards:
- 1 First Bite Black – 2 Hr (Total 4 Hr)
- 2 Then: Darker shadows – 1 hr (Total 2 Hr)
- 3 Shadows – 30 min (Total 1 Hr)
- 4 Mid – 15 min (Total 30 min)
- 5 Light – 8 min (Total 15 min)
- 6 Light 4 min (Total 8 min)
- 7 Lightest 4 min (Total 4 min)
- 8 White
Giving a total of 8 tones including White with a total of 4 Hours biting time. Each tone is double/half the time of the next. Hatching can be “interlaced” to create intermediate tones
Whilst the initial bite and lightest bites may seem extremely separated, remember that as you complete each successive tone, more and more of the plate is exposed, effectively accelerating the action of the acid.
I always think of acid as working like a group of hungry kids being let loose on an empty sweet shop; swarming around the brightest and stickiest sweets available and devouring them ravenously until too full to move!
- VARIABLES AFFECTING ACID BITING
- 1 Age of the acid – Fresh acid will have a relatively aggressive initial phase. Older acid will have a more sustained but slower bite.
- 2 Room temperature – Acid reacts quicker the warmer it is and in doing so will heat up even more. Allow anything up to 25% longer for cold acid.
- 3 Area of metal exposed – An evenly distributed and elaborate drawing will bite quicker and more evenly than a drawing with heavily worked areas and large unexposed areas; the acid will also be “attracted” to the heavily worked areas in preference to individual lines or details..
- 4 How long the plate has been worked on – No-one works in a sterile environment and so the older exposed lines will have been in contact with the air for longer. They will have oxidised or have attracted grease from the air or hand. This will mean recently drawn areas will bite quicker and deeper. A solution of vinegar and salt carefully dabbed over the plate with a cotton wool ball will freshen the older lines somewhat.
PREPARING AND SOAKING THE PAPER
There are several rituals I observe before printing: I tear the paper to the size I require (usually 2 – 3 inches bigger than the plate). I then place each sheet one by one in a the bath which I have half filled with warm water (I think it is absorbed into the paper better!) I have a large photographic developing tray on hand for transporting the wet paper.
While the paper is soaking I make sure I have everything laid out for printing; scrim (tarlatan), squares of tissue for fine wiping, card for applying the ink, rags for wiping the plate edges and of course my plastic fingers! Cut out of a large plastic bottle and folded these are perfect for handling (and keeping clean) wet paper and blankets and can be cleaned with white spirit if they get inky. Ink is squeezed out onto a sheet of glass and the pressure is checked on the press and the blankets straightened.
About a dozen large folded sheets of blotting paper are stacked for the wet paper and a pile of newsprint is at hand. For some obscure reason the blank paper used for printing newspaper is called newsprint, whilst the pages of old newspapers are … Just old newspaper! After soaking the etching paper is placed between the folded sheets of blotting paper and pressed until damp (if the paper is still shiny with water it is too wet and if it has started to cockle it is too dry. Too wet and the paper will reject the ink, too dry and the paper will not be pliable enough to be pushed into the line properly). I generally keep only three/four sheets in the blotting paper at any one time to ensure they do not dry out.
PAPER – DIFFERENT TYPES OF PAPER USED FOR ETCHING
Most paper that can be used for drawing can also be used for etching. However, as the paper has to be dampened before printing I have found it advisable to choose a heavier weight paper (around 200 GSM) as this will stay flatter after passing through the press and drying out. I always place each completed print between sheets of newsprint and then place a heavy board on top to ensure this. Below is a by no means comprehensive list of suitable papers. I have experimented with all of these and presently have settled on BFK Rives 250GSM White.
A printmaking paper designed for etching, silkscreen or letterpress. Mould-made 100% cotton rag, internally sizes and acid free with four deckle edges.
BFK Rives Blanc
mould made 100% cotton, watermarked, smoother and less sized than Velin Arches. Also available in black and 3 colours.
These papers are made at St. Cuthbert’s Mill. Originally intended as a printmaking paper, they have been discovered to also be highly suitable for pastel drawing. Mould-made 100% cotton rag, acid free with four deckle edges.
A watercolour paper that is 50% cotton rag and 50% wood pulp, surface sized and acid free with two deckle edges very white, available in 2 surfaces, watermarked. Suitable for many printmaking techniques.
Etching ink comes in various formats, the most familiar being tubes, but it also comes in tins and a more modern cartridge, which fits in a caulking gun. I now use 514B black ink from the Graphic Chemical & Ink Co. which comes in reassuringly traditional 1lb cartridges. I would avoid tins where ever possible as these are prone to dry up. inking a plate with ink that has dried out and formed a skin is a nightmare.
Inking the plate
I transfer ink onto the plate with small squares of cut up mounting card ensuring that the whole plate is covered and not just the bitten areas. Using the edge of the card the ink can the be scraped off the surface of the plate and used for the next print.
INK: Various inks are available for etching. And are generally categorised as being stiff or cold wiped. I use Graphical Chemical Bone black ink which comes in a practical 1lb cartridge.
Wiping the plate
This is one of the areas where experience and instinct kicks in and I have seen all etchers get it wrong at some time. The main characteristic of intaglio printing is that the ink is printed from out of the lines which of course means that the ink on the surface has to be removed. Invariably some ink will remain – this gives intaglio prints their distinctive plate tone. The danger is in over wiping the plate and losing subtlety in the etched image or under wiping and losing detail in the line work – the balance is a matter of personal choice and often becomes the style of each individual printmaker. It is this stage that prevents etching becoming easy to mechanise The plate is wiped with scrim (Tarlatan) in a circular motion without scrubbing too hard into the lines. Most of the ink will be removed this way and if a darker plate tone is desired a print can be taken at this stage. I usually wipe the plate further with small squares of tissue using the ball of my hand to obtain a cleaner print with greater contrast. Traditionally hand wiping used the edge of the hand in a sweeping motion with periodic dusting of whiting (ground chalk)to soak up ink on the hand and prevent dragging. The danger of this is that fine particles of whiting can find their way into the lines and cause unprinted spots. Finally I run a rag carefully around the BEVELLED edge of the plate and round the back to avoid ink being squeezed out from the back of the plate
After wiping with scrim the plate will still be holding a thin film of ink on the surface,. This will print as a very light grey. Traditionally this would be wiped again with the outside edge of the hand, which would be lightly dusted with ground chalk (whiting) to allow it to glide across the surface of the plate. The whiting will soak up the ink on the hand but care must be exercised that none gets on to the plate as it will block the etched lines that are holding the ink
Obviously the most important item in any etchers studio is the press. This consists of two heavy rollers a flat bed which passes through them, a large wheel or star shaped spindle which turns one of the rollers and powerful screw down clamps at either side of the rollers that control how closely they come together. The size of the wheel, or spindles gives the leverage to turn the roller (mostly often the bottom one) which moves the bed (mostly often heavy steel) through the rollers helped by the weight of the top roller forcing them together. Smaller table top presses may vary the mechanism using springs, a top driven roller, steel cased rather than solid steel rollers and a laminate bed, but in all cases the keyword is heavy! Most etching presses need a strong flat surface on which to stand and anything capable of printing a standard A4 sheet of paper will take at least two burly men to move. Basements are the favourite haunt of these beasts. Table top presses need a solid work table and to be securely clamped or screwed down, they are however nominally portable.
A set of lambs wool blankets, the bottom one fine and the top one thicker and coarser enable some give to the extreme pressure and push the paper onto the plate, so the ink is pulled out of the lines when the paper is peeled off the plate
The bed of the press is rolled out into position and the blankets are carefully folded back using the plastic fingers. A sheet of newsprint is placed on the bed and the plate is carefully laid centrally on top. Using a strip of card the width you wish the border to be, mark the distance from two edges of the plate with a pencil. The paper can now be carefully placed against the two pencil lines ensuring the print will be straight and central on the paper. Place a second sheet of newsprint on top, replace the blankets and turn the wheel to run the bed through the press. It is advisable to run the bed through in one fluid movement as pausing can show up as a line on the print. Adjusting the pressure of the press should be only attempted as a last resort and not as a remedy for sloppy biting or wiping! After running through the press gently roll the blankets over the rollers and peel the still damp paper off the plate, being careful not to smear the ink. Over the length of a busy print session the blankets will absorb water from the dampened paper and swell slightly this will alter the effective pressure and the blanket should be run through the press and hung up to dry overnight.
WATCHBELL STREET, RYE
View down the cobbles of Watchbell Street in Rye to the Hope and Anchor and Udimore in the distance. Watchbell Street was given its name because it was once the lookout across the bay to Camber Castle and the sea – for warnings of raids by the French!
Limited edition etching
8″ X 6″
edition of 50
Occasionally portfolios of etchings will feature various versions of prints from the plate taken as proofs to see what further work is needed. where big alterations are made the artist may actually number these transitional prints as States – Rembrandt etchings can often feature whole sub editions of these states.
Deriving its name from the etching process originally used to reproduce the washes of water-colours, aquatint works in the opposite way to standard etching. A fine resin powder is agitated in a sealable box using a paddle turned from the outside. After a period of time to allow the heavier particles to settle the box is opened (taking care not to breath in any of the powder). A degreased plate is placed face up on a mesh shelf and the box is closed. After allowing the fine resin particles to settle on the plate it is carefully removed and gently heated. This melts the coating of resin dust and bonds it to the plate’s surface. The dust particles form a permeable resist to the acid: each particle preserving a tiny island of the original plate surface round which the acid can bite. Stop out varnish ( a liquid form of hard ground) is painted on any areas required to remain unbitten, the plate is immersed in acid, removed, stopped out again for the next tone, and so on.
Depending on the density of the particle distribution, biting times can be very short; the resin forms what will eventually print as white dots against the much wider expanse of exposed plate
Preliminary work on the plate – sketching out areas requiring tones – can be lightly etched on to the plate using soft ground in much the same way as a watercolour can be lightly sketched out in pencil.
The final result of aquatint is fine white unbitten dots against a grey background and it should be noted each unbitten “pinnacle” of metal will be extremely susceptible to wear and the plate is unlikely to yield a large edition.
A similar but physically opposite way of creating steps of flat tone akin to aquatint is to run a plate prepared with hard ground through the press with a sheet of fine sandpaper face down on the surface. This will create the negative effect to aquatint, with the surface covered in a in a galaxy of pinpricks of exposed metal. The plate is stopped out in stages as with aquatint but care must be taken to cover the plate evenly and densely with dots, and that the pressure is not enough to scratch the plate (if the pressure is too great the small pinpricks in the hard ground will still be evident on the surface of the metal even in the stopped out (white) areas)
An domestic alternative to aquatint is car spray – acetone based as this will not come off in the acid or dissolve when stopped out!
AN ALTERNATIVE TO TRADITIONAL AQUATINT
I have in the past used acetone based car spray to create an aquatint but recently have discovered that small inexpensive atomiser spray bottles filled with a mixture of acrylic plate backing resist diluted with water will create a fine enough mist to give a more convenient alternative to a traditional aquatint. Place the degreased plate on a sheet of white paper and curve a funnel of corrugated card around it. Place a sheet of card on top and spray 18 inches above the plate in strong bursts. Any larger droplets should hit the back wall of card and the finer spray should fall evenly on the plate.(the white paper
should give an indication of the density). The resist is removable with methylated spirits allowing stop out varnish to be painted on and removed with white spirit with no harm to the “aquatint”
Mezzotint and Drypoint
Mezzotint is a printmaking process of the intaglio family, using the drypoint method. It was the first tonal method to be used, enabling half-tones to be produced without using line- or dot-based techniques like hatching, cross-hatching or stipple. Mezzotint achieves tonality by roughening a metal plate with thousands of little dots made by a metal tool with small teeth, called a “rocker”. In printing, the tiny pits in the plate retain the ink when the face of the plate is wiped clean. This technique can achieve a high level of quality and richness in the print.
Mezzotint is often combined with other intaglio techniques, usually etching and engraving The process was especially widely used in England from the eighteenth century, to reproduce portraits and other paintings. It was somewhat in competition with the other main tonal technique of the day, aquatint. Since the mid-nineteenth century it has been relatively little used, as lithography and other techniques produced comparable results more easily.
is a printmaking technique of the intaglio family, in which an image is incised into a plate with a hard-pointed “needle” of sharp metal or diamond point. In principle, the method is practically identical to engraving. The difference is in the use of tools, and that the raised ridge along the furrow (the burr) is not scraped or filed away as in engraving. Traditionally the plate was copper, but now acetate, zinc, or perspex (plexiglass)are also commonly used. Like etching, drypoint is easier to master than engraving for an artist trained in drawing because the technique of using the needle is closer to using a pencil than the engraver’s burin.
The lines produced by printing a drypoint are formed by the burr thrown up at the edge of the incised lines, in addition to the depressions formed in the surface of the plate. A larger burr, formed by a steep angle of the tool, will hold a lot of ink, producing a characteristically soft, dense line that differentiates drypoint from other intaglio methods such as etching or engraving which produce a smooth, hard-edged line. The size or characteristics of the burr usually depend not on how much pressure is applied, but on the angle of the needle. A perpendicular angle will leave little to no burr, while the smaller the angle gets to either side, the larger the burr pileup. The deepest drypoint lines leave enough burr on either side of them that they prevent the paper from pushing down into the centre of the stroke, creating a feathery black line with a fine, white centre. A lighter line may have no burr at all, creating a very fine line in the final print by holding very little ink. This technique is different from engraving, in which the incisions are made by removing metal to form depressions in the plate surface which hold ink, although the two methods can easily be combined, as Rembrandt often did. Because the pressure of printing quickly destroys the burr, drypoint is useful only for comparatively small editions; as few as ten or twenty impressions with burr can be made, and after the burr has gone, the comparatively shallow lines will wear out relatively quickly. Most impressions of Rembrandt prints on which drypoint was used show no burr, and often the drypoint lines are very weak, leaving the etched portions still strong. To counter this and allow for longer print runs, electroplating (called steel-facing by printmakers) can harden the surface of a plate and allow the same edition size as produced by etchings and engravings.
Line and tone
Half tone dots and hatching
For most printing processes printing is done off one surface and so using one colour effectively means any mid-tones have to be achieved by an optical illusion. With the mechanical half tone screen the original is photographed and the amount of light is separated by a grid into either black or white.
This is the way most commercial lithography is produced – the Dots per Inch measurement is the measure of how convincingly tones will be rendered:. A half tone of 300 DPI fools the human eye – 150 gives about newspaper photo quality and is less believable! The engraver working on a plate by hand creates the illusion of tone by using a similar method but with cross-hatched lines or stippling. As the metal has to be removed by physically cutting into the plate a certain consistent amount of force has to be applied – resulting in hatched lines of the same depth often running parallel and in many cases giving a mechanical or more controlled appearance. Accomplished engravers can be judged by the looser, fluid and more varied marks they use – reproduction bookplates and engravings that are copies of paintings are often noticeably more constrained and consequently lack the vibrancy of the original.
The obvious problem for the artist working in monochrome (most often Black and White) is how to avoid the overly mathematical patterns caused by half tone screening or the monotonous and systematic cross hatching used in reproduction prints. The Holy Grail of such artists is Continuous tone as best achieved in the traditional Black and white photograph.
Traditional photographs work on the principle of a flat surface covered by a fine grain that reacts to light. Each particle of grain is effectively analogue: it can be an infinite number of shades of grey (as opposed to halftone screening which is essentially Digital (Black or White). This photographic grain reacts according to the amount of light and the size of the grain – Fast film reacts quicker and is obviously grainier with less fine detail and higher contrast, slow film is more detailed. (Photographic papers work the same)
Controling tone through depth of bite
Etching is related to engraving in that it is an intaglio process; the ink is pulled out of the incised lines and deposited on the paper by the action of a heavy press as opposed to transferred from the surface, as in relief printing. The work of removing metal from the lines is done by the action of acid and is infinitely more controllable than the purely physical action of the engravers burin. For this reason the depth of lines can be precisely controlled so that they consequently hold varying amounts of ink. Whilst deeply bitten lines will be almost exactly the same width as more shallow ones (especially with Dutch Mordant on copper) they will print a correspondingly darker and richer tone. when I was exhibiting in wine bars and restaurants in the late 1980s I only had access to photocopiers for producing catalogues and flyers and so all my images had to be reduced to black and white. I thought that would be no problem with my etchings, but they almost uniformly came out heavy and dark, with no tonal differentiation – it was then I worked out why half tone screening is so important.
Cross hatching in layers
Using cross hatching in conjunction with a series of biting stages means closely hatched areas, lightly bitten can be “interlaced” with widely hatched areas heavily bitten to create rich textural tones unachievable in any other printmaking media.
The effect is to create an elaborate network of intermeshed “trenches” in the metal each dug to a specific level. These are far more delicate than standard hatched lines and can be subtly modified by burnishing to create new tones even within the existing tones.
The action of the burnisher rounds off the edges of the “trenches” lightening and softening the steps between tones to create smoky graduations ideal for clouds and for modelling contours.