Acid Patina. Any artificial coloring of metal in which an acid is employed. Because a large number of patina solutions are acidic, this is used for somewhat of a general – but inaccurate – term for all patinas. Those patina finishes for which acids are used in particular are torch finish and immersion finish techniques; torch where the acid is brushed on simultaneously with heating of the bronze with a blowtorch, and immersion patina where the object is totally immersed for a number of days. Among the 1,126 recipes for patina finishes listed by Hughes and Rowe in their 1983 work, approximately half are acid patinas. See patina.

References:

P6 {1983} Hughes and Rowe