I'm finding that if I underpaint the portraits that I work on they come out much better. The last few I've done I've underpainted with acrylic first and then applied the oil. However a screw up in the underpainting is very very difficult to hide with the oil. Oil tends to be translucent or even transparent and you just can't cover up a blunder of dark acrylic paint with oil. Not even with Titanium White which is supposedly opaque will do it. Obviously not really opaque.
Well if the oil is a very dark color like Umber Brown it can block out the acrylic under it as long as the acrylic is a lighter color, but anything lighter will not block out a darker acrylic under it. It shows through kind of like a shadow and I'm thinking that is the whole logic behind underpainting. What would be the need to underpaint if there were no effect from it.
What I'm thinking about doing Liz is the next time I paint a white animal like that white on that dog I did awhile back I'm going to underpaint it with blue acryllic and put the white oil on top. I believe it would give me the effect of the dog really looking white. It's worth the try anyway.
Ben Lustenhower a professional portrait artist says the same thing about oil paint. I'm sure he uses the very best quality paint. It's just a matter of knowing how the paint works and using it to your advantage.
The blue underpainting for the white dog seems like a good idea. If you get around to doing it, post the painting, I'm curious how it would look.
I was also thinking maybe the brand of paint affects how well it would cover over.
I didn't do a white dog, but I did use a blue/grey undercoating on the white of the tiger's fur and I'm really happy with the results. I think that blue or grey underpainting on a white animal is the way to go.