A foggy mask ruins an entire dive. Fog blocks a diver’s view of the incredible underwater world and impedes communication between divers. Fog can be dangerous. A diver distracted by a foggy mask can lose track of his buoyancy or his surroundings. It is possible to prevent any mask from fogging. However, new masks and used masks must be treated in different ways.
New Scuba Diving Masks: New scuba diving masks have residue left over from the manufacturing process coating the lens. Unless this coating is removed from the inside of the lens, the mask will constantly fog up no matter how much defogging agent is used. There are two good ways to remove the residue.
1. The Toothpaste Trick: Squirt toothpaste on the inside of the lens and rub it around with your finger or a soft cloth for a few minutes. The simpler the toothpaste, the better, so try to find a paste without bleaching agents and confetti. It may help to leave toothpaste in the mask overnight or to scrub the mask several times to allow the chemicals to react. Avoid using an extremely abrasive toothpaste or rough cloth, as these can scratch the inside of the glass.
The Flame Trick: Run the tip of a flame over the inside of the lens until the glass turns black, the flame will burn the residue off. A lighter or a tapered candle works well. Once the inside of the mask lens is totally black, wait for the mask to cool and wipe away the soot with a soft cloth. Repeat this process two or three times until it is difficult to get the glass to turn black. Do not allow the glass to become extremely hot, and do not attempt this trick on masks with plastic lenses (they will melt). Be sure to keep the flame away from the soft silicon skirt of the mask as it will melt with very little heat.
Used Scuba Diving Masks: Masks should be treated with a defogging agent before every dive. If treatment with a defogging agent does not prevent the mask from fogging, it is possible that some residue is left over from the manufacturing process. Try the toothpaste or flame tricks to remove the remaining residue. Any agent that prevents condensation from adhering to the inside of the mask's glass will keep the mask from fogging. See why defogging agents work. There are numerous options:
1 Spit: Spit on the inside of the mask and rub it around with your finger. Dunk the mask briefly in fresh water. The goal is to leave thin layer of saliva on the inside of the glass. Spitting does not work well if the mask dries out before diving, so use this technique immediately before the dive.
2. Commercial Defogging Agents: Commercial defogging agents are specifically designed to coat a mask's lens, and many divers find these products more effective than spit. Put a few drops of the defogging liquid in the mask, rub it around with a finger, and rinse briefly with fresh water. Remember, the idea is to leave a thin layer of the defogging agent inside the mask, so do not rub out the defog when rinsing the mask.
3. Baby Shampoo: Baby shampoo can be used just like commercial defogging solution. Many divers carry a bottle of watered-down baby shampoo with their dive gear. A few drops rubbed into the lens and then briefly rinsed out will keep a mask from fogging. Baby shampoo is preferable to standard shampoo, as it is generally hypo-allergenic, less irritating to eyes, and biodegradable. Baby shampoo smells good, too.
4. Glycerin Soaps and Dish Washing Detergents: Glycerin soaps and dish washing detergents can be used the same way as baby shampoo. Put a few drops on the inside of the mask, rub them in, and rinse briefly. If a mask leaks, it is possible that the water will carry whatever defogging agent is used into the diver's eyes. The one problem with these products is that they really burn the eyes. Glycerin soap and dish washing detergents sometimes are not biodegradable. Be sure to not dump any non-biodegradable defogging agents into the water.
5. Toothpaste: Rub a non-abrasive toothpaste on the inside of the mask lens until it coats the glass completely. Rinse the mask gently with fresh water until the lens is clear. If a diver is highly sensitive to minty fragrances, the air inside the mask may burn his eyes or cheeks during the dive. Before diving for the first time after using toothpaste as a defogging agent, wear the mask for a few minutes to make sure the fragrance is not irritating.
6. Potatoes: A cut potato rubbed on the inside of a mask lens has been said to keep a mask from fogging. Rub the potato on the glass, rinse briefly, and dive. This method is a bit of a diving urban legend, but feel free to test it out the next time there is a potato and a knife handy before the dive.