I have to paint the walls and trim in a house and they think the trim is painted with oil but not sure. Is there any way to test it?
Here is a simple test that works really well.
Use a clean cloth, painters rag, and denatured alcohol. Apply the alcohol to the cloth and gently rub the surface. If any paint is softened or removed then the finish is an acrylic or latex paint. If no color is on the rag and the finish is still unaffected then it is an oil base.
Use a white rag for checking dark colors and a dark rag for light colors. This will make it easier to see any removed paint.
Denatured alcohol readily dissolves acrylic and latex paints but leaves oil base paints alone.
Acrylic, latex, house paints cannot be applied over Alkyd, oil base, finishes without being primed first. However an Alkyd, oil base, house paint can be applied over an Acrylic, latex finish.
The easiest way to do that is try it with your thumb nail (not too hard)if it leaves a dent its latex if it is hard and doesn't dent its oil. I don't know about the rag with alcohol, oil paints degrade faster than the acrylics so it should leave a stain on the rag easier.
That really helps us to see what the walls are… latex or oil.. We just moved in the summer and not knowing whats on the wall.. Everyone should look into that before painting.