Oil mediums gone stiff

If it's dried up entirely, then it's too late, but how about adding some white spirits to it? This is what's used as thinner for Liquin. I don't know if Liquin is sold in plastic bottles, but in that case one should choose the glass bottle variant, because plastic isn't entirely airtight. Strangely enough, oil paints are also sold in plastic tubes, which can't be ideal. In fact, aliminium tubes aren't entirely airtight either, unlike lead tubes, still in use for Old Holland Classic Oils. But this is idiotic, of course. Mats

I should chuck the dammar varnish - though you can try heating it and the method you suggest is the safest way. Liquin can usually be brought back by vigorously shaking the bottle until you think your arm will fall off - or you can pierce the top, to see if it's just hardened on the surface; but if air has got to it, which it must have done, and it's hardened all through ... I don't think Turps will help and again, I'd throw it. I give my bottle of Liquin a good shake every now and then, and invert my bottles of stand oil (which I much prefer) just to ensure they don't dry right out. I also keep the bottles of both in a bureau - where it's dark - they seem to last longer that way (and Turps should certainly be kept that way, in glass bottles, preferably inside the cardboard box they usually arrive in). This sort of problem does arise when you've taken a break from oils for a while, and then come back and find your medium has dried out, or you didn't put the cap back on a tube of paint (or it just doesn't fit because of paint build-up on the thread): so far as the paint's concerned, a good poke with a toothpick (don't pierce the side of the tube though), will usually hit something soft and squishy....