Engraving and Etching

The same principals are employed today, though techniques have been refined and expanded. Etching grounds have evolved from an unpredictable waxy substance, to harder varnishes used by instrument makers, to petroleum derivatives like asphaltum. Early acids used on copper were made from a mixture of sulfuric acid, sodium nitrate, and alum, but they produced virulent fumes when used. Etchers switched to a weaker but safe mixture made from vinegar, salt, ammonium chloride, and copper sulfate. This solution produced rich detail, and was used by Rembrandt. Nitric acid was often used beginning in the late eighteenth century, but because of its strength, it sometimes destroyed fine details. Around 1850 a popular mixture was discovered consisting of hydrochloric acid, potassium chloride, and water. Sometimes called Dutch Mordant, it is still used today, and is the most widely used copper-etching agent, along with ferric chloride.

Plate usage has also evolved. The first etchings were done on iron plates, which corroded quickly. Around 1520, the Dutch artist Lucas van Leyden (1494-1533) began using copper plates, and other printmakers swiftly followed. However, copper plates can hold a lot of detail and are not expensive, but copper is too soft for large editions. In van Leyden's day, people used to pound it with hammers, creating a random alignment of the copper molecules, and thus a stronger plate. Today, copper can be bought in an already-hardened form. Better still, after etching or engraving, copper plates can be strengthened by putting a microscopically thin layer of iron on them through electrodeposition. This process is called steel facing.

In electrodeposition, copper and iron plates are placed in an electricity-carrying solution. Direct-current electricity is run through the plates, giving the copper a negative charge, and the iron a positive charge. The current removes iron ions, carries them through the solution, and deposits them on the copper plate. This technique, invented in France in the mid-nineteenth century, quickly spread throughout the world.

Zinc is often used as an etching plate because it is less expensive than copper. It is softer than copper, however, and requires a two-stage process for steel facing that results in some loss of detail. Zinc's softness can be an advantage in etching, where the plate is sometimes changed by scraping and polishing. It is too soft for fineline engraving, however.

Brass, an alloy of copper and zinc that is harder than either of them, is sometimes used for plates, and costs about as much as copper. Steel is the material of choice for engraving plates. Because it is so hard, very large editions can be printed. Steel also yields extremely fine detail. One disadvantage of steel is that it rusts easily. It must be stored carefully and protected from moisture with a coating of etching ground or oil.