Sadly not the 1970's rock band, but the colour Deep Purple. Here is Michael's description;
"After many years I was able to find a variety of this pigment that had a reasonable drying speed. It may interest some of you that I have PV 23 samples which I made in the late 1990s that still have not dried!! Deep Purple has tremendous use in all aspects of painting but should be used with caution by new artists as it has a tint power only matched by the Phthalocyanines. However, please do not be daunted by this description as when combined with whites it produces remarkable shades. Also, its slight addition to transparent yellows, such as Indian Yellow, can result in some extraordinary results that one can only describe as dark yellow which as a concept can be a little strange."
Pigment - PV23
Vehicle - Linseed Oil
Opacity - Transparent
Tint Power - High