Silver articles become black after some time when exposed to air because

Silver articles tarnish and turn black when exposed to air due to a chemical reaction with sulfur-containing compounds. While silver is a noble metal that does not react with oxygen even at high temperatures, it has a high affinity for sulfur [2]. Traces of hydrogen sulfide (H2S) or other sulfurous fumes present in the atmosphere react with the silver surface in the presence of moisture and oxygen [3]. This reaction results in the formation of a thin, greyish-black coating of silver sulfide (Ag2S) [2]. The chemical process is represented by the equation: 4Ag + 2H2S + O2 → 2Ag2S + 2H2O. Unlike copper, which forms a black oxide layer, or silver chloride, which turns grey in sunlight [1], the specific blackening of silver in ambient air is primarily attributed to this sulfide formation.

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.9 > p. 42
2. [3] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Activity 1.8 > p. 9
3. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 9: Distribution of World Natural Resources > silver > p. 34