"What can you mix with oil paint to keep the paint soft till the next painting day? I have heard of using oil of cloves. Does this work and where do you get it?" -- Ingrid OClove oil does work but it's perhaps not the best option as in the long term it darkens as it dries (see clove oil as a retarder for more details). I'd look for it in the health food section of a store as it's used for toothache.
I'd rather try dropping a little of whatever oil you're using as a medium onto the paint at the end of each day. Read more tips on keeping oil paint soft here...
Clove Oil as an Oil Paint Retarder, Or Not?
Freezing Oil Paints to Keep Them Soft
Readers Respond: What Do You Do to Keep Oil Paints Workable?