I have a problem that when I try to mix an oil base wash, with Grumbacher, burnt umber oil paint it will not dissolve with anything but water. I have tried Tamiya thinner, turpentine, turpenoid all to no avail. It just stays in the lump that squeezes out of the tube. If I do use water it will quickly seperate as soon as I stop stirring. What am I doing wrong? I have even tried another brand of oil paint, Winton and Newton and get the same results. I'd really appreciate some help here as this is really making weathering a hassle! I have had some small success adding some alcohol to the water but it just dosn't seem right.

Have you tried white spirit? It's what I use for thinning oils. I think it's called stoddards solvent in the US.

Erik

Thanks Erik, I'll see if I can find some and try it.
Gary