This brush is quite small (2°), flat, fine, and has a square point. It, too, is made of choice marten's hair. It is especially designed for lateral segmentation and is used to create the illusion of enamel cracks.
The flat shape obviously predestined the brush for that purpose. It is also possible to apply staining colors in order to mimic cracks on stress-bearing segments. A brush with a pointed tip would only permit the application of fine streaks of color. The square-pointed brush, on the contrary, permits small, colored patches, which give natural cracks the appearance of depth.
(G.Ubassy, Shape and Color, Quintessence Publishing Co. Berlin Germany ).

 

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