Silver, under normal conditions, will not be easily oxidized, even in a heated atmosphere. But the H2O in the air will sulfurate with SO2 or H2S and darken silver's surface. Silver's conductivity will not be deteriorated with only thin layer of sulfuration. But when the sulfuration becomes thicker, its conductivity and weldability will deteriorate.

To strenghten silver's resistance to sulfuration, we usually dip it into a solution of NaCr and NaCO3 (PH7.5~13) and apply a current of 80 amp/ft² for 5 minutes. Sulfurated or darkened silver can be cleaned by polishing or dipping into KCN solution.

Supplementary material for Electrical Contacts

Non-Iron material	JIS No.	Density	Melting point	%IACS Electrical Conductivity
Cu 99.90% Electrolytic Tough Pitch Copper	C1100	8.91	1083	100
Cu 99.96% Oxygen-Free Copper	C1020	8.91	1083	102
Cu 99.90% Phosphorus Deoxidized Copper	C1201	8.91	1083	100
Brass 70/30 65/35 60/40	C2600 C2700 C2801	8.53 8.50 8.39	915 905 900	28 27 28
Phosphorus Bronze PB1 PB2 PB3 PBS	C5111 C5191 C5212 C5210	8.86 8.83 8.80 8.80	850 910 880 880	15 12 11 15
Nickel Silver NS1 NS2 NS3 NS4	C7351 C7521 C7541 C7451	8.82 8.73 8.72 8.70	1110 1120 1100 1050	6.2 6.8 6.9 8.6