Silver when comes in contact with a boiled egg, turns grey or black. Why

 Silver is a well known name in jewellery and coinage.Silver also has the highest electrical and thermal conductivity of all known materials.

A shining silver metal, when comes in contact with a boiled egg, turns grey or black due to a change that is explained below

A boiled egg has certain levels of hydrogen sulphide generated while boiling due to hydrolysis of some sulphur proteins in the albumin and yolk.This hydrogen sulphide removes an electron from each silver atom when it comes into contact with silver while hydrogen gas and silver sulphide are formed.

During boiling of eggs, some trace amounts of sulphur are also obtained and are hidden in colloidal state in the wetness of the boiled eggs. Elemental sulphur, especially in decimated state, like in colloidal form, also oxidises silver to give silver sulphide.

In other words, the hydrogen sulphide and elemental sulphur present in boiled eggs oxidise a

portion of metallic silver to form a layer of silver sulphide. 

The natural colour of silver sulphide is dirty black. Hence, a silver plate turn black when a boiled egg is placed on it.