"Shaking Spray Paint" Topic

When shaking a can of spray paint are you just mixing the pigments or are you increasing the pressure in some way to make the paint come out of the can better?

Mike Bunkermeister Creek

You are mixing the pigments, with the propellant.
If you don't shake it, you will get sputter and inconsistency.
Plus, you will lose propellant, and have paint left over when the propellant runs out.

John +1

In combination with shaking, use the warm water trick. Fill a sink with warm water and let the can float in it for a few minutes shaking periodically. This will slightly increase the spray pressure, but also helps the paint to spray more evenly. Do this especially in cold weather or if the cans are stored in a cold space. Shaking the can itself does not appreciably increase pressure.

The analogy with carbonated beverage, for example, is probably suspect. Carbon dioxide dissolves in water so agitating soda releases more of the gas. Other gasses do not dissolve in water (argon, for example, which is why wineries that can afford it will sparge partially full tanks with that gas). I'm not a chemist so I don't know if aerosol propellant dissolves in liquid paint, but in any case I'm sure John the OFM and the others have got it basically correct – it's about paint coverage consistency and not spray can pressure.

I never said "dissolve". I said "mix".
When you're making cookies, you aren't dissolving the chocolate chips in the dough. You are mixing them. If you want to go to great bother, you can pick them out manually.
When I'm making stew, the bouillon does dissolve in the water.
Shaking the can mixes the pigment/paint with the propellant. If you let the can sit overnight, you should shake it again before using it.

Similarly, you always should shake the bottle of Italian dressing. Oil and water "don't mix", but they come together long enough to pour on the salad.

I never said that you said "dissolve." But what I said was true, (a) carbon dioxide doesn't just mix with water, it dissolves in it, and (b) that is not necessarily what is going on inside an aerosol can with paint and propellant.