Etching is the latest thing in 16th-century technology!
An image is worked into a metal plate by hand, and then printed on paper. Multiple prints can be made from the plate.
There are several etching techniques.  Mostly I use “line etch.”
  1. A copper, zinc, or aluminum plate is coated with a "hard ground," a tough, acid-resistant material.
  2. Once the ground has set, the artist uses an etching needle to scratch a design into the ground. The image on the plate is a mirror-image of what will be printed on the paper.
  3. The plate is soaked in an etching solution, such as nitric or ferric chloride.  The etching solution dissolves only the areas where the ground has been removed.
  4. The plate is inked, and the excess ink is wiped off, leaving only the ink in the etched grooves. The quality of each print is affected by how it's inked and wiped, how the pressure is applied, and how the paper takes the ink. 
  5. The inked plate is put on the bed of the printing press. A sheet of 100% rag paper, which has been soaked in water, is placed over the plate. The press is cranked by hand, pushing the plate between rollers, which causes the ink to be pressed into the paper. The edges of the plate become embossed into the paper.
  6. The etched lines can be modified, or even erased, by scrapping and burnishing the plate with special tools.
  7. When the plate is finished, and edition is printed. Each edition is limited to a predetermined number.  At the bottom of each etching, the artist writes two numbers, such as "8/50".  This means that the etching is the eighth of a edition of fifty.  At the end of the edition, the plate is usually defaced so that it cannot be used again.