How does the sulfur gas in the air influences to chip resistor? The main material of two terminals on a resistor is Ag and the sulfur transforms Ag into Ag₂S (Silver Sulfide). Shown here is the cross section of the chip, this Ag₂S disconnects the terminals. This sulfur gas penetrates into overcoats and plating level and meets Ag terminal and makes a chemical reaction. Users may find these reactions on the picture as a black or flower shaped mark(s).