I just came across this site http://www.tadspurgeon.com/puttymedium.php
Here, he has been creating a thick putty which should enable you to get the nice pastose brushwork of Rembrandt. It consists of chalk and elaborately prepared oil (washed manually, heated, put in the sun and what have we).
I am preparing some oil right now, but I am curious to know if any of you have tried it out. I am thinking about buying his book. Do you know if it is good?