These pigments run the gamut on lightfastness, weatherfastness, brilliance, and resistance to bleeding and solvents, often trading good characteristics in one area for another. As a whole, azo pigments tend to fade in tints with white and to bleed or be soluble in some organic solvents. It is therefore recommended that they be used only for glazing in full color for best permanence. Unfortunately, in the bright yellow range, there is little else to choose from today. The more traditional Cobalt yellow, or Aureolin, shows worse permanence than the azos with an ASTM lightfastness rating of II compared to a rating of I for many azo yellows.
Cobalt is reactive with organic pigments, having a tendency to turn brown.
In the reds it has become easier to find brilliant replacements for the cadmiums and azos. To a lesser extent, some Anthraquinone reds show good stability in the brilliant reds as well.