Originally Posted by oolong
I'm sorry but air does get into the bottles to equalize the pressure when you spray. If it didn't you would very quickly not be able to get any fragrance out. It is simple physics.
You will not get enough of a vacuum inside a small perfume bottle to override the pump/pressure cabability of the sprayer. How is air getting into the bottle? There are no bubbles coming up from the sprayer if i turn it upside-down and spray, no matter how many times i spray. And there are no bubbles coming up from the bottom of the tube if I spray it right-side-up - everybody who has eyes can see this. So how exactly is air getting in there? If it is coming in from the top/cap upon each release of the sprayer, why are no air bubbles produced when I turn the bottle upside-down and spray? As I said, if you turn it upside down and spray until the juice in the tube is emptied, you MAY then get an exchange of air in and out of the bottle and MAY get an equalization of pressure because of the way the pump mechanism operates. It is not "simple physics," it is simple mechanics and fluid dynamics.
Ever use spray-type concentrated laundry stain removers like Spray-N-Wash? Ever notice that the sides of the bottle tend to collapse inward a bit the emptier it gets? This is because there is no air getting in. A vacuum is being created. But the bottle is small enough and the trigger-pump powerful enough that the pump mechanism can overcome the vacuum pressure. Same concept.http://science.howstuffworks.com/question673.htm
Originally Posted by oolong
Chemistry tells you that exposure to oxygen will degrade a fragrance over time. While I agree that it will take a while, over time shaking the bottle will degrade the fragrance.
There is only one way oxygen might get into the bottle, as i described, and I advise not doing it because yes, over time, oxygen exposure will degrade perfume - I don't disagree with that. I am just pointing out that under normal conditions, you are not going to get additional air into the bottle AND most people (granted, BNoters don't necessarily fall into the "most people" category) will use the juice up before the air already in the bottle can do enough damage to noticeably change the scent. In other words, it's essentially a mute issue.
Assuming the pump works as I describe and that additional oxygen does not get into the bottle under normal use, wouldn't the juice degrade only to a certain point and then stop? I have only a basic knowledge of chemistry but I would not expect that an oxygen molecule could bind to a perfume molecule, destroy it (oxidize it; change its scent), and then move on to the next perfume molecule. Doesn't the oxygen molecule bind to the perfume molecule and essentially, stay bound? If so, I conclude that the small amount of oxygen left in the bottle at production time will only alter a very tiny portion of the juice, of which is not enough to cause a perceptible change, even over a long period of time.
Light and heat are the evildoers you have to watch out for. I say you will not detect a difference in the scent of a cologne whether shaken, stirred, or calm.