for the following reasons
1, cleaning ability: stone pickling, at the beginning is only part of the stone to quickly and effectively remove the dirt and impurities attached to the stone skin and a chemical cleaning method. Through different concentrations of oxalic acid (i.e., oxalic acid, chemical formula CO O H), hydrochloric acid (i.e., hydrogen chloride aqueous solution, chemical formula HCL) as a cleaning agent.
General water flushing stone, pebble, after oxalic acid or low concentration of hydrochloric acid immersion, the dirt of the skin and impurities included in the cracks in the holes can be quickly removed, off, and then washed with water after residual acid, stone skin will appear very clean, smooth, such pickling is only to remove dirt and scale, but also the essence of the stone, of course, should not be regarded as fake.
2, for fraud: some quite clever people, in the process of pickling, found some calcium carbonate rich stone species, easy to be corroded and dissolved by concentrated acid, so, \"pickling\" this is a normal method of stone cleaning, it gradually evolved into a means of fraud.