Von Kossa Calcium Staining Procedure Revisited

Probably the most sensitive and frequently performed stain for calcium deposits in mammalian tissues is the von Kossa, a stain used for over a century. When originally incorporated into daily use in the histopathology laboratory on paraffin tissue sections, the procedure called for immersion of tissue sections in an aqueous 5% silver nitrate solution and placed in direct sunlight for 20-30 min to make calcium deposits appear black. Although this effective method continues to be used in select locations, the modern laboratory often does not have access to bright sunlight. This study revisited the traditional von Kossa staining method with alternatives in light sources, silver nitrate concentrations, and timing of silver solution exposure and determined that a 1% silver nitrate solution is equally effective as a 5% solution in bright sunlight for 30-60 min. In addition, a 1% silver nitrate solution can be successfully used with exposure to a 3.5W light-emitting diode (LED) daylight lamp for 1 hr, sunlight through a tinted glass window for 1 hr, or overhead room lighting for 2 hr, and the staining reaction is unaffected by temperatures ranging from 1C to 40C.