Observations of onset of sulfide tarnish on gold-base alloys

In vitro Corrosion and Tarnish Analysis of the Ag-Pd Binary System

“…Such a plot is seen in Figs. 8 sharper, in that no detectable tarnish is observed in the Ag-Pd alloys with > 40%Pd.…”

Tarnishing of a Low-gold Dental Alloy in Different Structural States

“…Aqueous solutions containing sulfides, however, have been found to produce more tarnishing than with chlorides and various artificial salivae.2 These findings seem to correlate well with the results from an electron probe examination on 80 tarnished restorations where the tarnish was found to be essentially a sulfide intermixed with carbonaceous material. 3 Regarding the gold alloy itself, both Ag-3 and Cu-rich regions2 have been claimed to be the areas where tarnishing occurs.…”

“…3 The speed of rotation was 3 r.p.m., with the lower fifth of the diameter submerged in a solution consisting of 2 wt% Na2 S in water with a pH of 1 2. A sulfide concentration at that level was found necessary to give a visible tarnish within a reasonable amount of time.…”

Tarnish and corrosion behaviour of dental gold alloys

“…However, dentists occasionally reported gold-rich alloy restorations which tarnished in the oral environment. Electron probe analyses of several such restorations indicated that the tarnish product was a sulphide mixed with a carbon-containing substance (3). In order to simulate tarnishing in an accelerated immersion test, a tester was designed (3) in which a specimen is attached to a wheel which rotates in the vertical plane in such a manner that the specimen is immersed in a particular solution for part of each revolution.…”

“…In these specifications, alloys are classified according to their minimum contents of gold +PGM: 83 per cent by weight for Type I, 78 per cent for Type II (Vickers Hardness Number in the quenched condition 90 to 120) and Type III (Vickers Hardness Number in the quenched condition 120 to 150), and 75 per cent for Type IV. However, there have been occasional reports of tarnish in clinical restorations (3). Recent laboratory studies have confirmed that composition requirements alone are not sufficient to assure corrosion resistance (4).…”