HELMUT RUHEMANN'S INPAINTING TECHNIQUES
Pigments have to be permanent and compatible with each other, and with the medium used.
There are many such permissible pigments, but on the whole I prefer a fairly simple palette, as far as possible using earth colors with translucent additives. It is usually possible to restrict one's palette for any particular painting to very few pigments, often only four or five in addition to black and white, in the same way as the printer probably did.
The sharpness and bite of old oil paint can often be imitated only by adding traces of very transparent pigments such as Indian Yellow, Alizarin Orange, Alizarin Crimson and Bone Black. Although not absolutely permanent, it is permissible to use them in the small quantities needed.