I apologize in advance for a long winded question.
I paint thinly and I need these thinly painted parts to dry very slow: I cannot retouch them after they dry. I use walnut oil but not much because too much oil will not result in a texture I want.
I don't paint over this layer after it is dry.
I experimented with Grumbacher's Painting Medium II that slows drying, but it does not keep paint wet for amount of time I need, e.g. five-six days.
It is a combination of very little pigment and not much oil that makes the paint to dry too fast.
Also, slow drying colors like ivory black are not the colors I use in those passages. It's usually a relatively fast drying earth color.
Is there a medium or combination you can suggest to slow drying time beyond what walnut oil can provide?