I keep a small pair of pliers among my tubes of paint to use for stuck paint caps. The hardest part of the process is generally finding them!
Tip from: Marion Boddy-Evans.
Try placing the cap of the tube inbetween a door frame, then close the door over enough to hold the cap, then turn the tube! Works for me everytime!
Tip from: Ginger Marshall.
You can use a small piece of the rubber shelf-liner people use in their RVs to keep things from sliding around to open the top of a tube. It works better than pliers and does not damage your paint cap. I keep a piece (bought at WalMart) in my paint supplies all the time.
Tip from: Ruby Canody.
If you can't get the cap on your tube of paint off, snip off the bottom end of the tube and then keep it closed it will a bulldog clip.
Tip from: SkyChild.
I use nutcrackers to open stubborn tube caps, but if the tube begins to twist, boiling water always loosens stuck caps in seconds. Just plop the tubes head down in a cup. (Use the rest of the water to make a nice cup of tea or to fill your thermos for a plein air outing.)
Tip from: Carol Kerner.
When the cap on an acrylic paint tube sticks, just invert the tube and soak it for a few minutes in hot water; it should then loosen up nicely.
Tip from: Joan Smith.
If you can't get the cap on your tube of paint off, heat it with a match ever so carefully to loosen. After the cap is off, clean the rim and the cap, rub Vaseline (petroleum jelly or glycerine) around the rim and cap; it will work perfectly for years to come!
Tip from: Lila Ailuro.
When using a pair of pliers isn't working to get a stuck top off a tube of oil paint, try heating up the cap on the paint tube with a match for a moment or two. Then take a towel and twist the cap off. It works well, but do not keep the heat on the tube for a long time.
Tip from: Mark Rechenberger.
A simpler way to get a resistant cap off a tube of paint: hold the cap under the hot water tap for a minute or so, then turn it (possibly using rubber gloves for grip). It works every time.
Tip from: Harry Robertson.
The method for removing stuck paint caps I show my students is generally more immediate than soaking them in hot water or using a dangerous flame to loosen them. Squeeze all the paint to the top of the tube (like with toothpaste), roll up the bottom as far as it will go, grasp the tube firmly in one hand (I'm right-handed, so I grasp the tube in my left hand), and unscrew the stuck cap. If the cap has "sharp" ridges, then simply use a paint rag to unscrew the cap. If that fails, then use those misplaced pliers which should always be at your easel or in your paint box - I even recommend that my students get a cheap pair of pliers to keep in their paint box. When the paint is squeezed to the top and held firmly in place it prevents the tube from twisting and possibly splitting.
Tip from: Jim Meaders.
I keep a clothes pin [clothes peg] in my paint box. Simply place it around the cap, hold firmly, and twist. Works like a charm!
Tip from Cagney King.
I once put a number of tubes of oil paint away for a long time and, predicably, the stoppers couldn't be unscrewed when I retrieved them as the paint had hardened around te neck of the tube. I put these top-down in a jar half filled with domestic heating paraffin and left them there for a couple of weeks. After two weeks or so, the paint around the neck of the tube had softened and the stoppers unscrewed quite easily. I expect that any solvent can be used instead of heating paraffin.
Tip from: George de Bono
Tired of having your paint tubes crust up so that you can't open them? Try using some Vaseline (petroleum jelly) around the cap. According to a little old lady I met at a watercolor workshop, this will prevent the top from sticking.
Tip from: Jeremy.
I had the problem of opening oil paint tubes after many years packed away. I turned them upside down with the tops submerged in turpentine. The tops were freed up within a week or so. It's best to then clean any paint residue from the thread and cap and lightly oil with olive or cooking oil.
Tip from: Ian.
If I have to deal with a stuck paint tube cap, I fold up the bottom of whatever jeans I'm wearing and wrap them around the cap. It works as well as any pliers and it's harder to lose a pair of pants than a pliers!
Tip from: Franklin Driessen
I found a small kitchen tool called a 'crab cracker' will open any size paint tube lid. If it is stuck I twist slightly to the left and then unscrew it to the right. The crab cracker has two different sizes in one handle and it seems to work much better than my pliers. A nut cracker doesn't seem to be as flexible and my husband often has the pliers.
Tip from: Janece McKinzie.