How long can you effectively store a certain paint color in a sealed glass jar without it going bad?

What kind of paint? Latex or oil based?

Sorry Createx opaque and Pearl - water based

I have some paints that I've had for at least 10 years or better that are as good now as they were the day I bought them. If the container hasn't been opened it'll be good for a very long time as long as you don't let it freeze or get too hot.

Oil based in containers other than what they came in I usually take a teaspoon and add either a little Penetrol to cover the paints surface or boiled linseed oil, just pour it off before you use it and you're good to go. Latex is the same but I take a sponge and cut it to the size of the container, I then push it in and get it seated on the paints surface and then add water to expand the sponge, when you want to use the paint just pull the sponge out of the container and it's good to go.

Hope this helps.

Air is everthing whether its water or oil based.No air is good.Vacuum seal all your paint .

Btw teaser good call.Penetrol is great stuff.

And for plug sealing a 50/50 mix of Penetrol with Naptha beats anything else out there.Penetrates insanely deep and dries within 12hrs.The turpentine and linseed mix takes up to two weeks(not 36hrs) to fully dry/cure.

Using any type of shellac based product is just wrong.Never understood why anyone would use Sealcoat to seal a piece of wood that will enter water or see any type of temp change.Shellac,dewaxed or not,ain't made to be exposed to water or temp changes...ever.