I've got this 2kg tub of Gamblin cold wax that's been sitting in the studio since maybe March. Not old. But the top layer has this weird stiff skin on it, almost rubbery, and underneath it's still soft. I scraped the skin off and stirred what's left and it seems fine but I'm not sure if the ratio's changed, wax medium is supposed to be consistent and if it's lost solvent or something I'll feel it in how the paint moves.

I know the official answer is keep it sealed, use it faster, don't let air get in. But I've got four paintings going at once and I don't work through it that fast. So do people just stir and carry on, or does this stuff actually degrade? Because I've had a tub that went completely hard after a year and that was done, but this in-between state I don't trust.