What is the actual purpose for storing in glass jars. I know this is curing it. But how does this process cure it to completion? How do you know when curing is done?

Curing is necessary to ensure that:
The chlorophyl had dissipated as much as possible
The THC has turn from inactive to psychoactive
The bud tastes good
The bud is burnable

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well put, couldn't have said it better

indeed.....

and curing never really ends....
Usually unless you sell your bud or need to take it along with you somewhere, you would leave it in the jar FOREVER well atleast until your done smoking it hahahaha.....

I usually put them in the jar after about 10 days of drying, seal the jar for 12 hours and burp it open once...
after that... i only open the jar to get a little amount to last 2-3 days which i put in tiny jars... and leave the big jars alone...
after about 2 months.. if i still have a jar full i put it in the fridge.. Making sure that it is really well sealed so no humidity can enter the jar and rest in the bud... which would call for mold......

No curing..= Average bud.....
Cured= DIVINE!!

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Ok thanks for your input!

Got to talking about this on another thread. I skipped to where I was yapping about the curing process:

The real secret behind jar curing is how the product dries. If you left the product out on a table the moisture in it would dry up almost completely, from the outside in. When you use jar curing, you are limiting the amount of moisture that can be dissipated from the product until the next time you open the jar. What this does to the product is allows for a more controlled drying, or curing. Once the moisture in the product fills the space occupied by the air with humidity within the jar, no more evaporation can occur. (What happens next is where a lot of old school growers swear is the secret when it comes to maximizing your potency in the curing stage.) Moisture in the product is not just drying, there is a lot going on, sugars are breaking down, and acids are mixing to create the potent THC. Once the air in the jar is filled with the humid air from the product, very little evaporation is going on inside the jar at this point. Instead, the moisture is being wicked from the stems, leaves, everything, to the buds. (basically it is drying from the inside out in a way). So, on a slow cure like this, you are getting as much out of the stems and leaves that you can, instead of a faster type of drying where there might be some potent THC making compounds still inside the plant.

Jar curing basically allows you to allow the product to dry while giving the product time for the sugars to break down. If the sugars break down too quickly, or are forced to simply be evaporated, you are missing out on THC. If the moisture is brought out of the product too slowly, mold will occur.

As far as 'when it is done', that's all up to the person enjoying the product. (Since it should be able to barely be smoked when you put it in the jar in the first place) I have a couple different ways that let me know.
Weight: (This is highly debatable in the area I live due to the massive amounts of weed and money that go through here, more water weight = more money, sometimes when you get an opinion from someone who sells pot for a living, the tips might be a lot different from the ones given to you by a grower who grows it for personal pleasure)
Stickyness: more or less to your taste. Most of the people I know cure it to where it just barely sticks on your fingers. When you roll a joint, the paper should just slightly stick to your fingers, just enough to not let the paper slide around in your fingers. If the paper is sticking to this finger, and that one...let it cure a little more. Again, personal preference.
Third is how it looks, you are starting to over dry your weed when it starts getting more and more brittle. It shouldn't fall apart if you bump the bud around, or drop it on a plate. Rub some nuggets in the direction of growth a few times on different buds with your finger and thumb, there should be some resistance on the nuggets as they break apart.
Fourth is how it smokes or eats. Try a little when you first put it in the jar, everytime you open it smoke a joint, or eat something with it. You'll feel it get more potent as the sugars break down and the curing process continues.

When to stop curing is a personal preference.

Hope this helps explain it a little bit.