What is Acid prickling in Electroplating?

Answer 1

Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale, from ferrous metals, copper, and aluminum alloys.[1] A solution called pickle liquor, which contains strong acids, is used to remove the surface impurities. It is commonly used to descale or clean steel in various steelmaking processes.

In jewelry making, pickling is used to remove the oxidation layer from copper surfaces, which occurs after heating. A diluted sulfuric acid pickling bath is used.

Source:
http://en.wikipedia.org/wiki/Pickling_(metal)
http://www.b2cjewels.com/metalguide.aspx