A silverpoint drawing is one in which the drawn line is created with a thin silver wire held in a stylus. A specially prepared surface is necessary to provide sufficient abrasion to remove silver from the tip. This surface can be achieved through a variety of methods on a variety of substrates, the simplest being a thin coat of white gouache painted on paper.
Values are created with patient cross hatching and layering of strokes rather than application of pressure which may tear the paper.
Over time the drawing oxidizes to a warm glow characteristic only of this medium.
Other metals used traditionally are copper and gold, each leaving a mark with slightly different color and oxidizing characteristics.
Although it is somewhat difficult to see here most of my silverpoint work has text related to the piece partially visible in the background.