Dissolution of metals utilizing an aqueous H.sub.2 O.sub.2 -H.sub.2 SO.sub.4 -thioamide etchant

A method of metal dissolution which comprises contacting a metal with an aqueous solution containing from about 0.2 to about 4.5 gram moles per liter of sulfuric acid, from about 0.25 to about 8 gram moles per liter of hydrogen peroxide and a catalytically effective amount of a thioamide additive having the general formula ##STR3## wherein R is either an aryl or a heterocyclic group and the aryl group is selected from phenyl, alkyl substituted phenyl groups containing from 7 to 10 carbon atoms and amino substituted phenyl groups and the heterocyclic group is selected from those containing at least one nitrogen atom in the ring structure.