How does mask anti-fog work?

[ChrisA]

I figure the reason a mask fogs up is that the inside of the lens is at a tempure below the dew point of the air inside the mask. So water
condenses on the inside of the lens. So how does de-fog (spit or
whatever) prevent this?

My first guess is that the stuff (spit, 500PSU, kelp juice....) afftects the water surface tension alowing the litle droplets to merge and form big droplets that roll of the lens, Or maybe it makes the lens less "sticky" so the condensed water rolls off.

I really don't even know why the condensed water on the inside of the lens stays in place Perhaps the antifog prevides a hydrophobic coating.

I could go on and propose many theories but maybe some one knows the answer.

[MechDiver]

A mask will fog due to particles on the inside of the lens. Antifog cleans the lens so there is nothing for the condensation to adhere to. All I have ever used is spit. As long as you clean the glass, it doesn't matter what you use.

MD

[H2Andy]

what a great question! it had never occurred to me to ask...

and thanks for the quick answer, MechDiver

[getwet2]

:06: I always used spit until I tried an antifog product, gold seal I believe it's called, it works way better than spit. I never thought about how it works, never really cared. I see from your profile that you are an Imagineer, so is this what you guys think about when you're staring through your mask at 60'? Maybe try some different dive sites that are more interesting! Just kidding, interesting question.

[scubasean]

:06: I always used spit until I tried an antifog product, gold seal I believe it's called, it works way better than spit. I never thought about how it works, never really cared. I see from your profile that you are an Imagineer, so is this what you guys think about when you're staring through your mask at 60'? Maybe try some different dive sites that are more interesting! Just kidding, interesting question.

Not sure how it can be "better than spit", at least in my case. Spit works quite nicely for me. I use it before every dive and never get fog. So, price is the only factor, and spit is free.

[Scubakevdm]

Anti-fog works due to the priciples of molecular-tension and cohesive dynamics. Simply stated, the anti-fog molecules repel water molecules by giving them the finger and timing the punchlines of very funny jokes to cause them to shoot distinct streams of milk or soda from each nostril. This is why the worse your breath is, the better your spit works as defog. I have bottled mine, and am making it available for a modest fee. Please PM me with any requests.

[theskull]

Anti-fog works due to the priciples of molecular-tension and cohesive dynamics. Simply stated, the anti-fog molecules repel water molecules by giving them the finger and timing the punchlines of very funny jokes to cause them to shoot distinct streams of milk or soda from each nostril. This is why the worse your breath is, the better your spit works as defog. I have bottled mine, and am making it available for a modest fee. Please PM me with any requests.

Yes, I have a request. . . and for a modest fee I will reveal what it is.

theskull

[jimisurf]

I little trick I learned from the divemasters in Thailand is to use baby shampoo. It seems to work as well as any of the defogs or spit (maybe even Scubakevdm's spit, I think...:-). It smells reasonably good too. > Jimi

[cancun mark]

90% of comercial defog is a tiny bottle of very expensive watered down dishwasher liquid.

Most of the time in the ocean spit works fine, but if you use suncream or (ladies) makeup, itputs a greasy layer on the inside of the glass, and you need the soap to break the surface tension.

I have one of those soap dispensers that you get in bathrooms on the side of my training pool, as there is always a layer of suncream on the top of any swimming pool, and I use regular anti bacterial liquid soap in it. It works great.

I did just have chance to use some comercial stuff recently though, and it seemed to be a little more like gel toothpaste mixed with soap. The mild abrasive helps.

The toothpaste trick for new masks breaks the surfactant layer used during the manufacturing process of the glass. When they make glass, they float it on top of molten metal to get it flat, but they need some kind of wax so it doesnt stick. This wax is why new masks fog up.

One other way to break in a new mask is with a cigarette lighter and burn this wax off, just be careful you dont burn the silicone skirt off too.

[crispos]

90% of comercial defog is a tiny bottle of very expensive watered down dishwasher liquid

Do you know that for a fact, cancunmark? You know, I was just looking at the bottles of Sea Drops (www.mcnett.com)
and thinking what a great business that is, selling them for $6 a pop. Great thread.

I would have thought it was glycerin, also used in K-Y jelly, which conjurs up alot of possibilities...

http://www.pioneerthinking.com/glycerin.html

As glycerin seems to be a by-product of soap manufacturing, you may be correct in substance. So indeed it is acting as a surfactant of sorts.

I think ChrisA probably has the mechanism of the fog formation right. It would seem to me that the warm breath of the diver hits the cold mask face. I don't think you need particles for that to create the condensation, although agreed the initial coating on the glass definitely enhances droplet formation. The glycerin dissolves the water molecules rather than allowing condensation.

At depth no more mask equalization occurs and the air in the mask gets colder and it stops fogging.

Probably the pool students continue to fog the mask because they keep taking it off at the surface to clear the fogging up, or they wash the glycerin off during the mask clears.

We can't use spit in the pool due to the usual rules against this.