I associate Cobalt pigments with blues and violets not yellows, however thanks to Nikolaus Fischer who in 1848 created this semi-transparent straw/mustard yellow pigment we now have Cobalt Yellow also known as Aureolin.
Herr Fischer, maybe unwittingly, created a less fugitive alternative to the popular yellow colour Gamboge, whose beautiful, mustardy yellow hues are visible in Aureolin.
It's semi-transparent nature makes it excellent for glazes and as with so many transparent paints their true beauty is only revealed fully in a glaze, it's tint's are quite mid-value in temperature neither too green or orange. It has decent tinting power so provides a wide range of hues when mixed with white.
With the opaqueness and fiery nature of Cadmium Yellow this yellow with almost the opposite qualities really has a place on most palettes, it some how feels more natural and has a more earthy look than other yellows.
The source of the pigment is the UK where it is manufactured in very small batches.
Pigment - PY40
Opacity - Semi-Transparent
Drying time - Medium to fast
Binder - Linseed Oil