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Etchings are made from metal plates. The image to be printed is scored into the plate and ink is pushed into the groove. The raised surface is wiped clear of ink. Dampened paper is pressed onto the plate, resulting in the ink within the groove being transferred to the paper. By contrast, when a rubber stamp is used to make an impression, it is the raised surface of the stamp that is inked and the impression left on the paper will be of this raised area.
Plates are etched by placing them in a mild acid bath. Before a plate is placed in the bath, its surface is coated with a fine layer of bee's wax or bitumen. The image to be etched is scored into the wax, which is soft and therefore requires hardly any pressure to be removed. Very fine lines are possible using a needle-point stylus. Scoring the wax effectively exposes the metal beneath the wax. When the plate is immersed in the acid solution, the exposed portions of the plate are etched by the acid, while the rest of the plate's surface remains intact. The wax is then wiped clear and the plate made ready for printing. Every print requires the plate to be cleaned, re-inked and put through the press, manually.
It is possible to create tones on a plate by dusting the cleaned surface of the plate with finely powdered resin. The plate is heated slightly, causing the resin dust to adhere to the metal surface. Dipping the plate in a mild acid solution will cause the plate to be 'bitten' around the fine grains of the resin. The longer the plate remains in the acid, the deeper the pits in its surface will be, resulting in darker tones. Different depths of tone can be created by covering portions of the plate in successive stages with liquid 'ground'1.
Those areas that are to remain white must be covered before the plate is dipped in acid. The lightest tone requires about thirty seconds in the bath, while five minutes ensures a rich solid colour. Plates processed in this way are called acquatints. Even after the tone has been applied, it is possible to vary its effect by applying a burnishing tool to the surface of the plate, flattening out the grain..
A great deal of subtlety and complexity can be achieved in the way that ink is applied to the plate. Different artists have different techniques. The simplest approach to producing two or more colours on one plate is to use one colour of ink for the 'intaglio' or grooved portion of the plate and another colour on the surface, using an inked roller. Masks of tracing paper can be used to protect areas of the plate from the roller.
In a viscosity print, the plate is prepared in such a way that ink can be made to settle at varying depths within a single groove. Using rollers of increasing hardness, a transparent medium is laid into each of the different depths of the groove, followed by a layer of ink. The medium protects each layer of ink from mixing with any successive layer. If such a plate is planned and inked precisely, it is possible to see each distinct colour, perfectly registered and printed, in one impression.
Another technique is to use thin coloured papers cut into the desired shapes, rolled with glue and positioned on the plate, glue-side up. When the paper is passed through the press, the coloured paper sticks to the surface of the paper, with the ink riding over it. It is also possible, though rare, to use separate plates for different colours.
All the prints made from one plate (or plates in the case of multi-coloured prints) are collectively called an edition. It is only when prints are made by a manual process such as etching, lithography, silk-screen, linocut and woodcut, to name a few, can they be called original prints. An original print must bear the seal (often embossed) of the studio in which it was printed, the signature of the artist, the date and a number revealing how many impressions were made in the edition and a number representing the order in which each print was pulled. Typically this notation is made in the lower left hand corner beneath the printed area.
For instance, in an edition of ten prints, the first would be numbered 1/10, the second 2/10 and so on. The plate deteriorates in the course of printing so there is sometimes a difference in price between the first and final impressions in an edition. Copper-plate etchings tend to be produced in larger editions (often 100 to 250 impressions) than zinc-plate etchings because a zinc plate deteriorates faster than copper.
It is up to the artist to decide whether all the impressions of an edition are similar enough to deserve to belong within the edition. If there is a significant variation, then the print is declared an AP, meaning Artist's Proof. Such prints typically have a different (lower) value than edition prints from the same plate. Some artists prefer to work exclusively in APs, which results in each print being valued as a unique and original artwork, just like a drawing or painting.
When an edition has been completed, the artist is obliged to cancel the plate by scoring a line through it and the studio is expected to take one final impression from this cancellation plate, to keep a record of it. It is possible to confirm whether a plate is truly an original print or a commercial reproduction which is being sold as an original print, by checking the edition numbers with the studio. There are additional notations used to identify various other types of impressions permitted in connection with an edition.
It is worth knowing that commercial reproductions, such as posters or fine art reproductions, which are created by mechanical processes and printed in the thousands cannot be called original prints even when they are signed individually by the artists. The conventions governing the sale and notation of original prints were brought into force in Europe in the early years of the 20th Century, when print-making gained popularity as a valid art form. There are of course art-dealers and artists all over the world, who resist these conventions.