The biggest problems that I've had in achieve an oil are with all white and all black colors (I think I have a decent solution for the white). I then had an inspiration for black. I isolated the black colors from the rest of the image and set it aside and oil rendered the remaining part of the image. I then lightened the dark layer and applied my brush stroke technique to this layer. I then used GIMP's map function for this layer and cleaned the edges up a little before merging this layer with the other. The complete rendering can be found here: http://home.att.net/~lylejk3/Birthday_Bash.htm