A technical dictionary of printmaking, André Béguin.


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Etching

outline of the article

 
1. DEFINITION AND BRIEF HISTORY OF THE TECHNIQUE.
2. MATERIALS AND WORKSHOP NECESSITIES.
  • A. POLISHING THE PLATE.
  • B. GROUNDING THE PLATE.
  • C. DRAWING ON THE PLATE.
  • D. ETCHING OR BITING THE PLATE.
  • E. INKING THE PLATE.
  • F. PRINTING THE FINISHED PRODUCT.
  • G. WORKSHOP NECESSITIES.
3. THE FIRST STEP: DRAWING ON THE PLATE.
4. THE SECOND STEP: BITING THE PLATE.
1. DEFINITION AND BRIEF HISTORY OF THE TECHNIQUE.
Etching is one of the most important of all intaglio techniques. In many languages the term for this technique was derived from nitric acid diluted with water which the alchemists called
aqua-fortis. At present the term etching is used more generally since it is not limited to etchings done with nitric acid only. Thus etchings done with iron perchloride come under the same name. Furthermore, it is quite difficult to determine after the fact the kind of mordant used to make a particular etching. Generally speaking the term etching is used to denote the process, the plate on which it is done, and the impression itself. Etching may be opposed to other intagho techniques done using tools (gravers, burns, dry points, etc.) as it is a technique of engraving in which the plate is worked by a mordant. Aquatint* , crayon* manner , and sugar* lift are all types of etching in that they use a mordant to attack the plate but, since they are each characterized by particular procedures, one usually refers to them by their precise name. The making of an etching may be broken down into three distinct steps:

  1. Drawing, either with a point on a previously grounded plate or else with a brush charged with some ground or varnish. The outcome is the same in both cases even though one is the reverse of the other.
  2. Biting the plate (which has already been drawn on) so that the mordant etches the metal plate in those areas where it is not protected by the ground.
  3. Printing the plate. Printing is done by placing the ink in the hollows of the plate followed up by cleaning or wiping those parts that must not bear any ink. The pressure of the printing cylinder is such that the paper is forced into the intaglio parts of the plate where it picks up the ink.

Of these three steps two are almost always carried out by the same person; drawing and biting. The reason is that biting must faithfully render the drawn image and because of this one should consider the drawing and biting phases as being part of a whole. If the image drawn on the plate is a copy of an original drawing then the drawing and biting may be done by a person other than the author of the original drawing. Such work, usually called reproductive work, is very rarely done at present as photochemical processes have replaced most manual reproduction.
Etching is the engraving process most readily used by painters and because of this etching is sometimes referred to as
painter's engraving. Contrary to line engraving done with a burin or a graver, etching requires relatively little technical knowledge and because of this painters adopted it very readily. Further more, etching has become almost synonymous with what the French call "gravure libre" [ "* engraving gravure libre"] and which in English may be called "free engraving" because it can be done quite spontaneously, like a drawing. Etching may therefore be considered to be in opposition to line engraving hich is done by specialists as it requires a more rigorous technique. Thanks to the relative ease with which etching is done it became an artist's medium as of the 16th century when Parmigianino began the tradition of artist-engravers. It has been said that etching was invented by Wenzel von Olmutz, a German goldsmith of the end of the 15th century, but etching had already been practiced by the Arabs during the Middle Ages in Spain and at Damascus in order to decorate their weapons. At the beginning of the 16th century etching was used to make plates but "sometimes an irregular line and the thickness of the ink (in relief) makes one think that etching might have been done as of the end of the 15th century. Furthermore, a manuscript of 1431 written by Jehan Le Bègue (to be found in the Bibliothèque Nationale , Paris, ms . lat. 6741) seems to suggest such early usage. In other words etching might have been practiced a full hundred years before Urs Graf, Dürer , Mazzuoli of Parma (known as Parmigianino), and Lucas of Leyde who are usually considered to have been the first to use the technique (cf. André Blum, Les origines du papier, de l'imprimerie et de la gravure, p.164).
In any case Urs Graf began etching in 1513. In 1515 Dürer did his first etching "the Man of Sorrows" which was followed up by five more etchings some of which were the "Abduction of Proserpine on a Unicorn" (1516) and "Landscape with Cannon" (1518). Dürer worked on iron plates which presented a major problem since they rusted easily.
Etching came into its own in Italy after 1530 thanks to Francesco Mazzola (known as Parmigianino) who used this technique with remarkable verve. In fact he was the first to make the famous "free engravings" of artists which were distinct from the engraving done by artisans. In the course of time such free engraving was to be called original engraving. A pupil of Parmigianino, Antonio da Trento, exported the technique to France where it was used above all by the Fontainebleau school. Etching then spread to the rest of Europe in the second half of the 16th century.
The 17th century was the golden age of etching. The engravers who worked for Rubens used the etching technique along with graver work (etching being used to prepare the outlines of the plate). Van Dyck, a student of Rubens, drew some extraordinary portraits on plates which were unfortunately somewhat spoiled by the "corrections" made by professional engravers.
Jacques Callot, Hercule Seghers (who had a very contemporary taste for the technicalities of the process), and Elsheimer (all three masters of printmaking according to Henri Focillon) contributed significantly to the development of this technique and especially to what may be called the "spirit" of etching. Abraham Bosse, on the other hand, thought of etching in a very different way. As a professional line engraver his only aim was to imitate the precision of line engraving which he knew so well and considered to be the nobler art. Thus he ceaselessly sought to imitate, by means of etching, the well cut line usually attained with a burin or a graver. In his treatise on the various ways of engraving, published in 1645, Bosse explains in great detail how to etch so as to obtain a line resembling one cut with a graver.
The type of ground he worked with (in general use as of the times of Jacques Callot, who had first adopted it) was a varnish used by string instrument makers. It was a hard ground that allowed for a sharp line scratched with a point. After Bosse this hard ground was progressively abandoned in favour of a softer ground much the same as the one used today. This softer ground allowed, and still allows, for a softer line better suited to the drawings made by painter-engravers.
More or less at the same time as Bosse tried to "put order" into etching, Rembrandt, who was four years younger than Bosse, began etching and gave the technique a new dimension. History of art is at times marked by a miraculous coincidence between an artist and a technique. Dürer's line engravings, Ingres' lead pencil drawings, and La Tour's use of pastel are such coincidences. Rembrandt is identified with etching more than any other artist due to the ease and strength with which he worked this process. His knowledge of this technique was due to a meeting of affinities, a revelation. " Rembrandt needed only a short spell as a helper of Liévens to know far more than his master" (Claude Roger-Marx,
La Gravure).
In France, 17th century etching was dominated by the
landscapes of Claude Lorrain who had a lasting influence on his time. Landscape etching was further developed by Ruysdael while Potter and Van Ostade etched animals and scenes from peasant life.
The 18th century was essentially devoted to etching of portraits. It was the century of Watteau, Boucher, Canaletto, and the Tiepolos, but it was also the century of the greatest French etchers such as Gabriel de Saint-Aubin who foreshadowed, in is treatment of light and his sheer nervous strength, present day work. The 18th century saw also the etching of Piranesi whose strange universe is made of grandiose monuments and prisons. Finally, it was the century that saw the birth of the various manners derived from etching. During the second half of the century appeared the
crayon* manner on soft ground, the lavis manner or brush etching, and aquatint, all of which were used in connection with colour printing.
Goya begins 19th century etching. His country was not known for engraving and he himself did not begin to engrave until the second half of his working life when he began to go deaf and his vision of the world became increasingly dramatic. Rembrandt had repeatedly etched his self-portraits, looking into a mirror, appearing as a disheveled, mocking, slightly peasantile person. Goya's self-portraits show a well dressed man in profile with a bitter expression around the mouth. Both, however, show the same supreme ease with this medium.
According to the Goncourt brothers (who were also engravers besides being literary men) the 19th century was the century of the "Aquafortistes" the term they coined to designate etchers. In 1862 the
Société des Aquafortistes (Etcher's Society) was founded and was joined by such artists as Manet, Jongkind, Legros, Degas, Pissaro, Courbet, Boudin, etc. In the course of the 19th century and even in the 20th century many artists turned to etching despite the competition coming from lithography which, since the beginning of the 19th century, offered what seemed to be greater possibilities for both painters and drawers.

2. MATERIALS AND WORKSHOP NECESSITIES.

The materials needed by an etcher are those used in the six different steps of etching: polishing the plate, grounding it, drawing on it, biting it, and, finally, printing it.

A . POLISHING THE PLATE.
The plate most generally used is made of
copper since this metal offers the best results especially insofar as concerns biting and wiping (before inking). However, zinc plates must not be underestimated. When used properly zinc is an inexpensive and supple material to work on. Furthermore, zinc is particularly appropriate for the test trials needed to build up one's experience with etching. If some of the trials are particularly successful it is always possible to have the plate copper faced or steelfaced so that large quantities of impressions can be printed. Steel is another metal that may be used for etching but it tends to give rather hard and cold lines [ metals ].
Today plates are usually bought ready for use being already polished to a mat or brilliant finish. One may, nevertheless, wish to do the polishing oneself and a partial or total polishing is often necessary during or after work on the plate [
polishing ].
The materials used for polishing are
abrasive sheets, charcoal , a scraper , one or more burnishers , some mineral oil , and oil.

B. GROUNDING THE PLATE.
Grounding a plate is a delicate operation which conditions both the drawing and the subsequent etching or biting. Etchers have a variety of
etching grounds available each one being appropriate to a particular task.

  1. NORMAL GROUND. Normal grounds are the black ball ground, soft ground, or what may be called a brush ground since it is applied with a brush.
  2. RE-BITING GROUND or STOP OUT GROUND. Such grounds are used for further bitings and are various types: roller ground, ball ground, or liquid ground.
  3. COVERING GROUND. Such grounds are used for protection of the back and sides of a plate. They are not suitable for drawing on.

The role of these different grounds will be examined further on. The reader may also turn to the article devoted to etching* grounds where the ingredients of these grounds are discussed. Etchers must have various brushes (a big one for grounding the whole plate and both medium and small ones to cope with details), dabbers* , a roller* for applying grounds, a vice* , tapers* to blacken the plate, and a hot plate (or at least a source of heat).

C. DRAWING ON THE PLATE.
To do the drawing all that is needed are the fine and thick etching needles with which to cut into the ground or even into the metal plate itself. As far as the sizes are concerned, one may use anything from the fine etching needles to points that are bevelled and which are called
oval points or echoppes (not to be confused with the mushroom handle oval points used for line engraving).
However, it is quite useful to have various tools used for other types of engraving such as
burins , oval points , roulettes , a scraper , and a burnisher to flatten out the incorrectly cut lines. Finally, one should have some abrasives and a wetstone for sharpening the tools.

D. ETCHING OR BITING THE PLATE.
For this operation one must have an
etching basin whose dimensions should be larger than the plate to be etched. Generally speaking two etching basins of different sizes are usually needed. Remember that a small basin is not much good since one needs a generous mordant bath to disperse the used mordant. In the case of re-biting when the plate is not completely immersed into the mordant, one may use the wax damming method. The pouring technique is no longer used but when it was still in use it required a wooden easel "in order to hold the plate at the right angle to pour the mordant over it" (Bosse). The mordant was then gathered in a kind of trough from which it ran into an earthenware receptacle. The mordant was poured from a stoneware jug
The most commonly used mordants are
nitric acid and iron perchloride. The reader will find a full description of the various mordants below whereas their makeup is explained in the article on mordants.
The article on
attacking agents is, on the other hand, devoted to a general description of acids and salts.
To begin with, it is best that the etcher have a sufficient amount of pure (40B) nitric acid and of 45B iron perchloride. Furthermore, a
pigeon feather, a brush or a badger hair brush with long supple bristles will be needed to stroke the plate during biting. Place a water basin close to a water faucet making sure that it is not far away from the etching basin.
A set of
funnels and filters will be necessary in order to put the mordant back into its container.
The work must be done wearing
rubber gloves or at least wearing a rubber finger. An hydrometer is essential in order to make precise mixtures and doses [attacking agents].

E. INKING THE PLATE.
An inking slab is a necessity and gives the best results if it can be slightly heated. Always have available a reserve of
ink for printing etchings (there are several types, see under ink) and some oil which is used to prepare such inks. Furthermore, one must have one or two inking dabbers , some tarlatan to wipe the plates, and some rags. Finally, it is necessary to have a palette knife to mix colours on the inking slab.

F. PRINTING THE FINISHED PRODUCT.
It is not necessarily the etcher himself who prints his plates but it must be said that the work is much simplified, especially insofar as concerns possible corrections, if the etcher does his own printing. When the etched plate is quite finished it may, on the other hand, be simpler to have the impressions made by a professional printer who will do it more rapidly and may be even better. Thus, an etcher might do well to have an intaglio
press for his trial impressions.
For printing one must have
paper , a water basin , blotting paper to be used for drying the paper, and a brush to clean the sheets of paper [ dampening]. One must also have a free surface on which to dry the impressions and some boards made of compressed wood shavings [drying].

C. WORKSHOP NECESSITIES OF AN ETCHER.
Without being a full fledged laboratory, the etcher's workshop is perforce bigger and more elaborate than the workshop of an engraver who uses only tools to work his plate. This is especially true if the etchings are relatively big since it will be necessary to have a rather large space for the various mordant baths and rinsing facilities. Satisfactory results and a certain amount of safety are not compatible with cramped quarters. The basins and spaces used for the different steps in making an etching must be arranged in such a way as to avoid detours and loss of time. Furthermore an etcher must keep in mind the problems raised by acid vapours and thus must have some kind of
airing system.
Finally, an etcher working on a grounded plate must have a
screen to light up his work [studio].

3. THE FIRST STEP : DRAWING ON THE PLATE.
First make sure that the plate to be used has been properly scoured. In the best case, when the plate is already clean, one need only degrease the plate using turpentine oil and cellulose paper. When it is dry follow up the cleaning by rubbing with some tissue paper. In case a more complex cleaning has to be carried out turn to the article on
scouring.
The ground will only adhere to the plate properly when all traces of grease have been removed. If oily traces remain accidents will happen both during the drawing phase and during the biting.
Applying the ground is a delicate operation. In fact the layer of ground must be well distributed, thin, and adherent. In order to attain this one must heat the plate on a hot plate. The heating must be just right and can be checked by putting a bit of saliva on the plate which should come together and bubble at the same time. One must not heat the plate any more than this because the ground might burn.
The ground must not boil when being applied since this will make it brittle and crumbly after drying. If one notices that the ground boils when being applied wait until the plate has cooled off somewhat.
Deposit on the plate a quantity of ground sufficient for the amount of biting foreseen. The plate must be held with a wooden handled vice (or a vice entirely made of wood) so that the plate does not burn the etcher's hands and in order to keep the plate stable, especially when
dabbing. The vice must be padded with some protective layers of cloth or cardboard so as not to damage the plate when it is being gripped. Of course, if there are to be no margins on the plate it will be necessary to take the vice off at one point or another so that the entire surface can be grounded.
When the plate is warmed to the right temperature pass the black ball ground over the surface of the plate making sure that the distribution is the same all over. After putting down the ball (which has to be in a gauze bag in order for the larger particles not to be lost on the plate) spread the ground with a silk dabber stuffed with cotton. The dabbing process (preceeded by a slight heating of the pate must be done regularly, beginning in a corner and moving along the plate. The dabber must he used quite firmly and can be used as long as the ground is hot. When the plate surface cools off the French say that the dabber "sings", the reason being that the dabber becomes hard to pull away from the plate and makes a characteristic ripping noise. When this happens the dabbing must stop and the plate grounding must have been finished.
It is quite difficult to repair a badly done ground by just re-heating the plate. If one notices that there are some mistakes it is easier to remove the ground with benzine and scour the plate again.
The ground may be laid with a
roller in which case the roller must be very clean and the ground must be of the type suited to rollers.
One may also ground the plate using a
brush. This is the simplest way of laying a ground but, on the other hand, it is also the system that gives the least satisfactory results. In fact, the ground laid with a brush is much less resistant than the preceeding ones, especially when the biting is a long one.
Such a ground tends to crack and split both during drawing and during biting despite the fact that commercially made grounds available at present are of superior quality.
Thus it will be best to use a brush ground only on etchings that are to be lightly bitten. A brush ground is applied on a cold plate.
When the copper plate is still lukewarm proceed to blacken it.
Smoking or blackening a plate was, in the past, practically indispensable. At present many etchers do not see the reason for doing it even though the smoking is far from being useless. In fact, by moving lit tapers* back and forth under the grounded side of the plate (the plate being held upside down for the purpose) one blackens the ground which then will show up any drawing done on it, even if the lines are very slight. The plate must be held with a hand held vice or suspended above the tapers by means of rings holding the corners of the plate. If one does not blacken the ground it will be found that upon cooling even the darkest ground will be only light brown in colour.
If the smoking or backening is done immediately after laying the ground when the plate is still lukewarm the resulting finish on the plate will be quite
brilliant. If one waits for the plate to become cold the result will be a mat finish. Generally speaking and personal preferences put aside, it must be said that the blackening works better on a lukewarm plate. However, one must never heat the ground too much with the tapers since it might crack open. Large format plates are difficult to blacken. An improperly done blackening is even harder to remedy than a poorly done grounding. Usually it is simpler and more expeditious to remove everything and start over again.
Once the blackening has been done may proceed to draw on the plate. Two possibilities exist: either direct and improvised drawing or a
tranfer* of an original drawing. In both cases one must keep in mind that the impression will be in reverse as compared to the image on the plate [ reverse ].
There are various ways of transferring a drawing by contact onto a grounded plate [
tracing , transfer]. The main advantage of improvisation is the spontaneousness of the drawing. Insofar as tracing is concerned it is very easy indeed since the etching point scratches through the ground in the same way as a crayon draws on paper. According to the fineness of the point used, the pressure applied, and the closeness or superimposition of the lines the etcher will obtain, after biting, lines that are more or less wide, deep, accentuated, or intense. Blacks are obtained by crossing lines. The depth of the lines can be varied from simply scratching the ground to cutting into the plate itself (through the layer of ground). The reader should be reminded that the wider a line is the more lateral and superficial the biting will be. If two lines are too close to each other the biting (especially if prolonged) will tend to wear away the ground separating them and will cause a burst-through* or crevé.
In this case a burst-through will turn the two black lines into a grayish spot because a hollow surface with a flat bottom will keep only part of the ink when the plate is wiped.
I do not counsel working on a grounded plate when it is too cold since it makes drawing more difficult. Etchings that are drawn in summer are, in many cases, more beautiful than those drawn in winter or in a cold studio. If the temperature in the studio is too low one can slightly warm the plate that is to be worked on another plate that is just lukewarm. By heating the ground in this way the drawing will turn out to be quite precise without being too rigorous.
There are two main techniques of actually etching the plate: one in which the biting is done all at once and another in which the biting is done several times over (re-biting). The first technique requires that the entire plate be etched after having been grounded in the way described above. For this kind of etching different sizes of etching points are used in order to give different sized lines (thinner, thicker, or crossed).
Re-biting is done in several steps with the aid of a stopping out varnish. Some of the etched lines are stopped out when they are judged to be sufficiently bitten and then the rest of the plate is re-bitten. Thus a plate can be re-bitten several times over beginning with the thinnest lines and progressing towards the deeper ones, the first and thinner lines being stopped out with a quick drying varnish.
It is also possible to etch "backwards" using the technique of re-biting. Thus one begins by biting the lines that will be the deepest and progresses to those that are more superficial and fine. If one chooses this procedure the first lines to be etched will be exposed to all of the bitings carried out on the plate.
As the reader can see etching is not a strictly defined working procedure but rather a technique that affords a great deal of freedom.
The etching needle is not the only tool used to scratch through the plate surface. Etchers may also use
roulettes or try out textile grains and abrasive grains. One may also paint directly onto a plate using a brush and some liquid ground or an oil base ink. Such ground or ink may also be put on the plate by means of splatter work.
An etcher must work according to the result required after the biting has been carried out. In this sense an etcher is always less sure of the result than a line engraver or a dry point engraver. When the latter two work their plate the resulting image will be exactly the same when printed whereas the etcher must still contend with the biting process. In fact, biting may cause a real transformation of the plate. Some etchers deliberately use the imponderables of the etching technique, searching for surprises in chance happenings much like the surrealists who, influenced by psychoanalysis, saw particular meanings in just such chance arrangements. Thus one can leave a large part of the work to unknown reactions between materials, to an impulsive decision, and to apparently incompatible combinations in order to achieve an extraordinary result...or something of no interest at all. In any case etching is the engraving technique that leaves the greatest amount of latitude for the inventiveness of a painter.
An etching can have any kind of line: regular, parallel, crossed, crossed to form squares, crossed to form lozenge shapes, etc. Etching can also have a great variety of
granulated* textures, achieved by projecting or printing with different types of wood, vegetable substances, all kinds of objects, spots, etc. Anything can be tried out. The final test is the impression and from it alone may one judge the success of one's work. The artifices so readily allowed for in etching will not stand up to judgement unless they are accompanied by talent, taste, and intelligence.
More practically speaking, lines will print according to their depth and width. The deeper and narrower a line is the better it will hold ink and thus the blacker it will print. The wider and shallower a line is the more it will "give up" the ink when the plate is wiped and thus will print gray with darker borders. If one wishes to have wide spaces that print quite black it will be necessary to engrave or grain these hollow spaces themselves so that the ink will be retained during the wiping and the impressions will be black.

4. THE SECOND STEP: BITING THE PLATE.
Before beginning to bite the plate make sure that the ground is perfectly dry. A dry ground will become mat when breathed upon. If this does not happen wait some more. A ground that is not sufficiently dry will cause accidents during biting. The next step is to cover the back and sides of the plate with an appropriate ground [
etching ground].
The etching bath (solution) may be prepared according to the instructions given in the article on
attacking* agents, mordants*, and biting*. Whatever mordant is chosen (usually nitric acid or iron perchloride (ferric chloride)) one can bite the pate in three different ways: by immersion , by covered biting , or by pouring the mordant.
The immersion technique requires that the plate be completely immersed in the mordant. Covered biting can be done either by brushing the mordant over the plate or, after building up the sides of the plate with some wax, by pouring the acid into the container formed by the plate and the wax dam.
Biting done with the pouring method calls for an easel on which to place the plate almost vertically and then the mordant is poured onto the top part of the plate washing down all along it.
It would be worth while to revive the pouring technique which at present is hardly ever used. In fact it presents certain advantages compared to the other two techniques: the used mordant, charged with particles of bitten metal, is immediately washed away and the bubbles formed by the biting process on the plate surface are removed, making the biting more even. Evenly done biting is essential in order to obtain a clear and precise etching. Of course, as we will see, it is possible to achieve even biting using other biting techniques but not as well. Furthermore, the pouring technique (as well as all vertical biting) is more rapid than horizontal biting.
If one chooses the wax damming system be sure that the wax adheres properly to the plate. One way of making the wax stick properly is to pass a hot key, for example, along the inside edge of the container formed by the wax. One must also have a way to empty the "basin" when the biting is done. This may be done by pushing an oiled pencil through the wax dam and leaving it there until the emptying has to be done.
If the plate is to be etched in a basin remember to put the mordant in before the plate and not inversely has to be done. as is the case in
aquatint* or when a plate must be watched closely during biting. In this case (the latter one ) the mordant is poured in until it barely comes up to the level of the plate and then the basin is rocked back and forth. To come back to the normal etching, the immersion of the plate must. be done all at once by sliding it into the mordant by one of its shorter sides, much in the same way as a diver enters the water, making sure that no splashing occurs. If the bottom of the basin is not already in relief one must glue some plastic rods to the bottom so that it will be possible to pick up the plate by putting a finger or stick under it. All manipulations which involve the mordant must be done wearing a rubber glove or a rubber finger.
After a short time the plate will be covered with bubbles in those areas where it is not protected by the ground. In case iron perchloride is used the plate wilt not bubble but it wilt turn black.
One must clean these bubbles and the blackening during the entire biting period since they act as a barrier between the metal and the mordant, thus weakening the etching. One must therefore "feather" or wipe the areas being bitten with a pigeon feather or with a badger hair brush.
The bubbles and the blackening also prevent one from watching the biting, which is a most important task. The biting should not be too rapid since this ruins the lines but one can speed up an overly slow biting by increasing the concentration of the mordant.
The effects of the mordant are determined by its concentration, by its freshness, and by the temperature of both the environment and the mordant itself. The degree of concentration is more closely studied In the article on biting as average strengths may be varied in function of need. If the mordant seems to bite too rapidly it can be diluted by adding some water and if it is too slow it can be reinforced by adding a more concentrated solution. One must, of course, make sure that such additions are made promptly and that they are quickly mixed otherwise some parts of the plate will be bitten more or less than others. One can also (as is done in grain photogravure*) use different concentrations of mordant, in different basins, in order to achieve bitings of different depths.
The freshness of a mordant can also be changed if one so wishes. Too fresh a mordant, one that has been used very little or not at all, bites nervously. This can be remedied by "ageing", by adding some filings of the same metal which is to be attacked. This kind of ageing must be done before biting. In the past such ageing was done by putting a coin into the mordant. Another way of ageing a mordant is to add some used mordant to it. The amount of used mordant (used mordant should be kept at all times) to be mixed into a new one is usually about 10%. If a mordant is too old or used (this is seen above all from its dirty colour and the irregular biting it does) one can freshen it up in an emergency but usually it is better to replace it with some fresh mordant [attacking agents, mordant).
Finally it must be kept in mind that temperature plays an important role. Heat and summer months activate and increase the biting. Too cold a studio (less than 18C or 64F) make the mordant bite very slowly. Changes of weather and approaching storms also have adverse effects on biting.
Biting time is variable and depends on all of the above-cited factors including the intentions of the etcher, the type of ground used, and the type of biting preferred (in one or several steps, by immersion, by covering, etc.). Some very slight bitings ("biting until boiling begins") may last less than a minute. On the other hand, Dunoyer de Segonzac at times etched his plates overnight with an extremely weak mordant. Nevertheless an average biting time using the more usual mordant concentrations (20 to 25B for nitric acid, 55 to 45B in the case of iron perchloride ) will be anywhere between two and fifteen minutes.
Biting properly is the result of a great deal of experience. Generally speaking it is better to withdraw the plate too soon than too late. When one removes the plate from the bath it must be immediately plunged into a basin of water or under running water from a faucet. Rinsing must be quite thorough, even if the plate has only been removed to check up on it. After drying with blotting paper examine the results of the biting. If one only wishes to check to what extent the biting has progressed remove a corner of the ground preferably in a place where the lines are crossed or where there are parallel lines. The biting may continue if the lines have not undergone any damage and if the areas between the lines are still intact. If one decides that the biting has attained the desired effects proceed to remove the ground.
If the biting is done by the wax damming method (which is only possible if the border areas of the plate are not to be etched) it is carried out in much the same way as above. However, it is not as easy a method since it will not be possible to rock the mordant back and forth and, furthermore, a certain amount of precautions are necessary in pouring the mordant onto the plate and then removing it again. If the plate is a big one the time it takes to pour the mordant onto it may bring about some irregularities in the biting process since it will begin earlier in the place where the mordant is poured and later on the other end of the plate.
Insofar as the pouring method is concerned: "... once you have put enough mordant into an earthenware container you may begin to scoop up the mordant using a stoneware jug or something else that is suitable. Pour the mordant onto your plate, onto its highest part, in such a way as to have the mordant spread to all of the plate. Make sure that the jug does not touch the plate. Once you have poured eight or ten jugs full, small jugs are used, stop and turn the plate around . now pour ten or twelve jugs of mordant before turning the plate around again... in this new position pour eight or ten jugs of mordant... continue to do this for about seven or eight minutes depending on the strength of the mordant and the characteristics of the copper plate " (Bosse). The reader must have understood that it is important to turn the plate around (upside down) so that the biting be regular and that the plate not be marked by the "runs" of the mordant. When the biting has been completed proceed to remove the ground with turpentine oil and wipe the plate carefully. For the time being one may leave the ground on the back and sides of the plate since it may come in handy if further biting has to be done.
The only way to find out whether a biting is successful is to print a state of the plate. It is fairly common that an etching needs to be worked somewhat more either because one wishes to deepen the lines or because one wishes to attenuate them. To diminish the lines one may try to close them up using a burnisher. If the lines are too deep they must be knocked up by hammering from the other side of the plate. Knocking up is done resting the plate on a steel anvil* and after having found the exact place that needs to be worked with callipers*. The hammering done on the plate during the knocking up procedure causes a little bump which must be removed with a scraper and then run down [polishing]. To deepen lines one can continue to bite or use such tools as burins, points, and roulettes. One must, however, take care to maintain the same over all character of the etching as the tools do not give the same result as biting. Tools are more precise and more mechanical than mordants (especially nitric acid) which give a more uncertain and lingering line. However, it is not forbidden to mix styles: burn work, some dry point, and graining may result in a new intensity of expression.
If one wishes to re-bite the whole plate one can ground it again on its printing side. This must be done making sure that the ground does not fall into the lines and hollows. In order to do this one must apply stopping out varnish with a roller, which is a very delicate task. The varnish used must be relatively thick, "like honey in winter".
If one wishes to re-bite only certain areas one may use a white ball ground or some other transparent ground so as to see the work that has already been done. White ground is not very resistant to biting and therefore the amount of biting must be limited. Such a ground is applied hot and using a dabber until the ground becomes cooler. A transparent ground is less easily scratched than many other grounds and the lines appear to be enlarged. If one wishes, a drying varnish may be used that is less transparent but more manageable.
During the supplementary biting make sure that the biting goes in depth and that the lines are not just being widened. In order for this to happen remove the ground only from the bottom of the lines. When etching is done using stopping out varnish and the technique of successive bitings the varnish is mixed with some lamp black to make it more visible and is applied with a brush. Remember that stopping out varnish is not as resistant as a ground and that its principle advantage lies in the fact that it dries quickly. Keep in mind its relative resistance when proceeding with further bitings.
The plate can also be bitten by applying some mordant to selected areas using a brush [brush etching]. In order to make the mordant spread properly either on a ground or on a partially cleaned area of the plate rub the area with a bit of saliva. The acid can be removed with some blotting paper.


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