Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Metal whiskers differ from metallic dendrites in several respects; dendrites are fern-shaped, and grow across the surface of the metal, while metal whiskers are hair-like and project at a right angle to the surface. Dendrite growth requires moisture capable of dissolving the metal into a solution of metal ions which are then redistributed by electromigration in the presence of an electromagnetic field. While the precise mechanism for whisker formation remains unknown, it is known that whisker formation does not require either dissolution of the metal or the presence of an electromagnetic field. Whiskers can cause short circuits and arcing in electrical equipment. The phenomenon was discovered by telephone companies in the late 1940s and it was later found that the addition of lead to tin solder provided mitigation. Restriction of Hazardous Substances (RoHS) in electronic equipment is driving the development of replacement alloys for pure tin and tin/lead alloys that resist whisker growth. Others have focused on the development of oxygen-barrier coatings to prevent whisker formation.