I had to use pliers yesterday to open my modelmaster and poly s paints. How do I avoid this I think it's the paint drying on the lip of the bottle.

After you are done painting, whipe the lip of the bottle off with a rag or watever you use to whipe your brushes on after cleaning. When I do this it helps alot and I hardly ever have to brake out the pliers.

First thing, never shake a bottle of paint. You shake the paint, it coats the inside of the lid. You lay the lid down, inside up, and the paint spreads out beyond the bounds of the lip of the bottle. You put the lid back on the bottle, and the paint coating the inside of the lid flows down and around the threads. Next time you need it, the lid is stuck.
Always stir your paints and store them upright. Many people will tell you to store the bottles upside down to keep the paint from drying out. Frankly, that's stupid. All the pigment will collect in the lid and makes a hell of a mess when you finally get around to using it. If a bottle of paint dries out, it's because the lid was not on tight and air got in, or, you haven't used that bottle of paint in a really (I mean REALLY) long time. And it's just aged it's self to death. And if it's that old, are you really going to be disapointed or suprised that it's dried out?
And finally, always wipe the threads of the bottle off before putting the lid back on. Simple cleanup and a firm grip and twist will keep your paint in useable condition for years and never a stuck lid.

hi no cure to old paint bottles but when you buy new paint bottles rub a candle round the treaded part of the bottle , stops paint from sticking the lid down cheers ian

If you get one that is particularly stubborn, turn it upside down and put a few drops of thinner on the edge of the cap and let it sit for a while. That usually enough to loosen it up.

If after trying various things to open a lid (like heating it up with hot water, the thinner suggestion, and using plyers), doesn't work, then I find that using a pipe wrench to open it up will never fail. I've yet to have a bottle of paint that I couldn't open with a pipe wrench. I'm not talking about those huge pipe wrenches, however, I'm talking about the little 6" ones.

I know that's not what you're asking, but I thought I'd mention it anyways.

My two cents worth
Cent 1 - Wipe it down before you put the lid on it.
Cent 2 - Use one of those rubber bottle openers that give you better grip. Pliers can ruin the lid by denting it making more space for more excess paint.

Ive tried all postings, but the easiest/cleanest method is to heat your stuck lids with a bic lighter, then one of the rubber bottle openers. Even the stubborn lids yield to the heat

Just after using that bottle, clean the lid with a rag. To prevent the paint from drying up, shake it atleast every 2 days.

Just be careful about using flame. You might get things on fire

Guys,
Be very, very careful when using tools to get the lids off. Three weeks ago I was attempting to get a stubborn cap off a paint bottle with a jar opener (V shaped tool with a handle on it) when the neck of the small bottle broke off in the lid and cut the hell out of my thumb causing me to have to get six stitches. The cut was so deep they were concerned about ligament damage. Now, after trying all other means of loosening the lids, I slip on leather gloves when using a tool to assist.

m38 - no fun man. That's gotta be a hard lesson to learn. Thanks for the reminder to be safe.