In tracing the cause of the discoloration of silver coins in museum showcases, the liquid in which these silver coins were washed was tested by ion-chromatography and X-ray fluorescence. The air pollutants and particulates around the exhibition room were also tested to identify where the ion and element components came from. The results showed that most of the inorganic ion like chloride, nitrite, nitrate and sulfate (Cl-, NO2-, NO3-, SO42) came from the pollutants in the air, whereas some organic acids like formic acid and acetic acid were discharged by decorative materials used in exhibitions. Electron spectrum and the scan electron microscopy were used to analyze the materials on the darkened surface of silver coupons which had been exposed in the exhibition showcases for a period of time. The results showed that the main elements comprised of carbon, oxygen and sulfur, with sulfur at a deeper penetration. The results proved that oxides and sulfides exist in darkened materials. Further analysis by infrared spectroscopy found high absorption of hydrocarbon, demonstrating that the surface of the darkened silver not only contained inorganic oxides and sulfides, but also some organic matters. This discovery explained the presence of carbon during the electron spectrum analysis. Simulation experiments compared different environmental conditions such as the concentration of air pollutants, relative humidity, light and lighting types. It showed that in highly polluted air in which F- and SO32- exist; the experimental silver coupon seemed to darken very easily even when there was no illumination factor. However, in standard air, the experimental silver coupons do not change color even in 100% RH and 2000 lux of illumination. This showed that among factors such as air quality, light illumination and relative humidity that cause silver to tarnish or darken, air pollutant is the main factor. This paper also explains why there is more sulfide than oxide and how easily this can be detected in darkened silver surface by comparing the chemical property of silver compounds. Results of the simulation experiments pointed out some reference points and measures to lower the concentration of pollutants in the air, and to prevent silver from being contaminated. This information will be useful in modifying environmental conditions for culture heritage exhibitions.