Series number: 1 Chemical description: Benzimidazolone color index name: PY 175 color index number: 11784 Permanence rating: A ASTM lightfastness rating: II Transparency/Opacity: ST Granulating/Staining: St The colors are chosen according to mass tone (color from tube), undertone (bias of color when in a thin film), color strength, relative opacity and the character of the pigment in water color, ie. granulating, staining or even wash. The resultant color spectrum ensures the largest number of colors can be mixed from the range. The optimum brilliance of every color in the Artists' Water color range is unparalleled by any other water color.