Mask fogging is not an unavoidable consequence of diving!
Mask fogging results from:
Under water the air inside a mask's face pocket is warmed by your face, while its glass face plate is cooled by the water. The layer of warm air that comes in contact with the face plate becomes cooler, and condenses into liquid water on the inside of the glass. Whether it forms that annoying fog depends on another factor however.
If water condenses on a hydrophobic (water repelling) surface, it forms lots of tiny little droplets. These droplets are the mask fog.
If water condenses onto a hydrophilic (water attracting) surface, it forms an even sheet which you do not notice.
Greasy substances are hydrophobic and cause masks to fog up. Hydrophobic substances typically encountered on a scuba mask are:
During the manufacture of most masks an invisible hydrophobic chemical residue is left on the glass. This makes the mask glass very prone to fogging. The residue must be removed by scrubbing the glass with a mildly abrasive cleaning agent like toothpaste. Scrub both sides of the lens. Your finger will do. If new masks (except no-fog models) are not scrubbed before their first use, they will fog regardless of other preventive measures. Avoid using mint-flavored toothpaste as it may irritate your eyes. Gel toothpaste may not be abrasive enough.
Warning! The above only applies to standard tempered glass masks, not to non-fog or prescription masks. Before scrubbing any diving mask, read the printed material that accompanies it. Non-fog, and some prescription masks (including gauge readers) can have plastic inserts which may be severely damaged by even mildly abrasive substances like toothpaste. These masks will usually be supplied with their own cleaner/defogger solutions.
Sun screen lotion, body grease, petrol and engine oil are always present in the diving environment
and build up on the mask, so you need to clean them off regularly.
Plain old detergent, shampoo and toothpaste do a fine job. Baby shampoo will not hurt your eyes if you forget to rinse the mask properly. Specialised cleaning solutions work well too.
Put a drop inside each lens and rub well, rinse thoroughly.
Clean your mask before every dive.
Don't believe it?
Try this experiment: rub a little sun screen lotion on to your mask glass, rinse with water, and go for a dive.
Control: wash your mask thoroughly with detergent, rinse, and go for another dive.
You be the judge!
Adding a commercial defogger also helps. Some defoggers include a cleaner. Defoggers basically leave a hydrophilic residue on the mask that breaks the surface tension. They come in many varieties, some are gels, others are solutions. Some must be rinsed off before use otherwise they sting your eyes. If the defogger does not include a cleaner, it is essential to clean the mask first. Popular defoggers include:
Plain old saliva is an effective defogger on a reasonably clean mask, but is not effective on a really greasy mask.
So you cleaned your mask glass with detergent, spat in it before you dived, and it still fogged up! Why? Common causes of grease accumulation are:
OK that is all fine in theory, but I'm in the middle of a dive and my mask is fogged up!
What to do?
Easy, just let a little bit of water into your mask, swill it around, and clear your mask. This should work, at least temporarily. If your mask fogs up too quickly, just leave a little bit of water in it. Not good enough? Well you can always take your mask off under water, lick it and scrub it with your fingers, some times this offers some relief. Too scared to do this underwater? - practice in a non-stressful situation.
Ron Henry 29/09/2008