Pigment Red 3 Toluidine Red shows insufficient fastness towards solvents; in fact, it is partially inferior even to monoazo yellow pigments, which is also true for other members of this class. Its stability to alcohols, aliphatic and aromatic hydrocarbons, and dibutyl phthalate equals step 3 on the 5 step scale; P.R.3 is even less fast to esters and ketones. P.R.3 is used primarily in air drying paints. Its hue varies considerably with the particle size, therefore pigment manufacturers usually offer a range of brands. The products with coarser particle sizes are bluer. Very bluish varieties, however, partially contain chemically modified P.R.3. Full shades of Toluidine Red are extremely lightfast and weatherfast, but deteriorate rapidly as the pigment is reduced with white pigment. P.R.3 application in printing inks is restricted; the pigments are being displaced by their stronger Naphthol AS pigment counterparts. P.R.3 is used primarily in flexo printing.