Pickling systems can be mechanical, chemical or electrochemical.

Mechanical pickling can be performed with silica sand, corundum, or with glass or stainless steel spheres.

 

The most energetic mechanical pickling can sometimes precede the chemical ones when the quantity of scale is of considerable thickness and is very adherent to the metal surface. In the case of chemical pickling, baths are usually used at temperatures above the ambient temperature and for times commensurate with both the size of the scale to be removed and its adherence. All pickling baths are highly aggressive and sometimes toxic (presence of hydrofluoric acid) and it is therefore absolutely necessary to set up the pickling systems with the appropriate safety systems and then proceed with careful washing of the artifacts and of the pickled parts in general. It is also necessary to avoid too long residence times in the pickling baths to avoid damage to the artifacts; if the scale is very adherent, it is better to alternate the pickling baths with a mechanical brushing action (with brushes of inert fibers or stainless steel wires) to facilitate their removal.