Cyanide could be blue metal. It is used in mining and associated with intentional poisoning and heavy metal/satanic bands.
Cyanide is mainly produced for the mining of gold and silver: It helps dissolve these metals and their ores. In the cyanide process, finely ground high-grade ore is mixed with the cyanide (concentration of about two kilogram NaCN per tonne); low-grade ores are stacked into heaps and sprayed with a cyanide solution (concentration of about one kilogram NaCN per ton). The precious metals are complexed by the cyanide anions to form soluble derivatives, e.g., [Au(CN)2]− and [Ag(CN)2]−.[
Niche uses
Potassium ferrocyanide is used to achieve a blue color on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of cyanide in the mixture varies according to the recipes used by each foundry.
Cyanide is also used in jewelry-making and certain kinds of photography such as sepia toning.
Cyanides are used as insecticides for fumigating ships.[30] Cyanide salts are used for killing ants,[31] and have in some places been used as rat poison[32] (the less toxic poison arsenic is more common).[33]
Although usually thought to be toxic, cyanide and cyanohydrins have been demonstrated to increase germination in various plant species.[34][35]
Human poisoning
Deliberate cyanide poisoning of humans has occurred many times throughout history.[36] For notable cyanide deaths, see Cyanide poisoning: History.
Most significantly, hydrogen cyanide released from pellets of Zyklon-B was used extensively in the systematic mass murders of the Holocaust, especially in extermination camps. Poisoning by hydrogen cyanide gas within a gas chamber (as a salt of hydrocyanic acid is dropped into a strong acid, usually sulfuric acid) is one method of executing a condemned prisoner as the condemned prisoner eventually breathes the lethal fumes.
Food additive
Due to the high stability of their complexation with iron, ferrocyanides (Sodium ferrocyanide E535, Potassium ferrocyanide E536, and Calcium ferrocyanide E538[37]) do not decompose to lethal levels in the human body and are used in the food industry as, e.g., an anticaking agent in table salt.[
https://en.wikipedia.org/wiki/Cyanide