Chemical machining method may be the oldest nontraditional
machining method which is used to shape copper with citric acid in
the Ancient Egypt in 2300 BC [7]. Until the 19th century this
process was widely used for decorative etching. The development of
photography provided a new dimension to chemical machining and
in 1826 J.N. Niepce was the first to use a photoresist made from
bitumen of Judea asphalt for etching pewter (an alloy of 80-90% of
tin and 10-20% of lead). William Fox Talbot (1852) patented a
process for etching copper with ferric chloride, using a photoresist
made from bichromated gelatin (GB Patent No:565). John Baynes, in
1888, described a process for etching material on two sides using a
photoresist which was patented in the USA (US Patent No: 378423).
The main industrial application of chemical machining
developed after the war. In 1953, North American Aviation Inc.
(California USA) used the process to etch aluminium components
for rockets. The company named the process "chemical milling" and
patented it (US Patent No: 2739047) in 1956 [8]. The machining
method is called in different names such as etching, chemical
etching, wet etching, etc.