In the 15th century it was discovered that an acid bites out metals and thus a representation can be made that can be used as a printing plate. A preferably copper plate is polished and provided with an acid-resistant layer, often consisting of beeswax or resin. The artist draws the image in the etching ground with an etching needle. The plate is then placed in an acid bath with ferric chloride or nitric acid, so that only the recesses are bitten out, thus creating a printing plate. The acid concentration and duration determines the depth of the grooves. The deeper the groove, the heavier the line will be. In between, you can choose to protect certain parts of the image with lacquer so that shallower or no grooves are created.
Rembrandt van Rijn, among others, often did not use wax, but scratched directly on the copper plate. In between, he often fixed prints in order to complete or even change the performance afterwards. This technique is called the drypoint technique. More burrs are left behind where the ink gets stuck. As a result, fewer prints are possible and therefore the works on paper are more unique. The quality of the paper is the next choice.
Printing is actually done the same as an engraving. You can see the difference, only with a magnifying glass, but in the line thickness and evenness of that same line. Etching lines are more irregular, more nervous. The copper plate is smeared with ink and then wiped clean again, so that the ink only remains in the grooves. Then a slightly damp paper is placed on top and, if necessary, a matted piece of fabric, is again placed on top, which absorbs the ink to the paper. With a printing press, the ink is printed on the paper.
With multi-colour printing, the process takes place in several steps, applying color by color as with Arnold Iger's work. The paper is often placed in a container so that the paper and thus the print does not move while printing. With an intaglio technique you often see the print on the edges of the printing plate, so you can recognize that this technique has been used.
The first edition that an artist approves is given the 'predicate' AP: Artist Proof of EP: Épreuve d'Artiste. Of course we can have more of that in between. Subsequently, it is determined how many prints will be made, which the artist then signs and numbers.