ABOUT BLACK SCRATCHBOARD

Scratchboard (North America and Australia) or scraperboard (Great Britain), is a form of direct engraving where the artist scratches off dark ink to reveal a white or colored layer beneath. Scratchboard refers to both a fine-art medium, and an illustrative technique using sharp knives and tools for engraving into a thin layer of white China clay that is coated with dark, often black India ink. Scratchboard can be used to yield highly detailed, precise and evenly textured artwork. Works can be left black and white, or colored. 

Technique

Unlike many drawing media, where the artist adds in the mid-tones and shadows, with scratchboard the artist is working by adding in the highlights. The artist can use a variety of tools to scratch away the black ink from the board and reveal more or less of the white clay that is underneath.

After black ink has been removed as desired the work may be colored with watercolors, airbrush, colored pencils or acrylics. Transparent media are generally used to color scratchboard, as they fill in the white scratches without affecting the black ink left on the board. Artists that begin with a white clay-coated board will add their own ink to the surface, and then scratch away the ink in the same manner as described above. After completion, the artwork may be varnished to protect it against damage.

(Wikipedia)