Tips On Painting Fixit Sculpt?

I patched up a spot in a smooth cast 300 replica I made. The fixit sculpt is a grey and the smooth cast a pure white. I was using a “wash” to color/paint the rack. Using oil colors mixed with lacquer thinner to stain/paint/wash the white rack to a normal color.
Problem is that the gray fixit sculpt isn’t staining/painting like the rest of the rack.
Any hints? Will I have to actually spray paint the fixit sculpt with white paint and then wash/stain it?

 

Here is one spot. The other is spot is on the antler tip.

 

So maybe airbrush the epoxy with white acrylic? Then stain with oil wash and then seal?

 

Thanks for the tips!

 

So last night I painted the two fixit sculpt areas with air brush. Then I hit it with a blow dryer for about 15 minutes. Waited about two more hours and then started to try to wash on some Van Dyck Brown oil paint thinned with lacquer thinner. My testors acrylic white that I had airbrushed on came loose in a few spots when I went to wipe the wash off. Frustrating!

So I took all the paint off and used lacquer thinner to clean it off really good. I had wiped it really good to get the oil paint off from before but I didn't clean it with lacquer thinner.

So I am hoping that if I lacquer thinner it off really well before I repaint ton the acrylic that next time the acrylic won't come off when I try to stain/wash it in oil and lacquer thinner.
Am I on the right track? Or will lacquer thinner want to remove the acrylic? Just trying to save a lot of wasted time and money.

Any hints are appreciated.