A chemical cleaning composition for silver- or copper-containing surfaces
consists of a water-soluble solid or powder comprising thiourea or a
derivative thereof, and is formulated in unit application form, e.g. in
tablet or sachet form. A preferred composition comprises up to 60%
thiourea or a derivative thereof; up to 4% surfactant; not more than 40%
acidifier; less than 20% disintegrant; up to 10% binder; 0-1% lubricant;
and up to 40% diluent.