I can distinctly remember my first day at my open water dive class, when our dive instructor asked us all to spit into our dive masks and put them on. Eyebrows went up in disbelief everywhere, and not to mention a few chuckles as well. When we asked our instructor why, his reply was simply “to prevent your masks from fogging up underwater.” We accepted this and proceeded with our class and found out quickly that the spit really did work well.
But have you ever stopped to wonder why spit? What makes ordinary saliva so effective against fogging of masks? Why do masks fog up in the first place? Why won’t simple water do the trick? To answer this, we have to get a little technical.
A Scuba mask fogs up when the inside of the lens is at a temperature below the dew point of the air inside the mask. So water condenses on the inside of the lens. But the explanation doesn’t stop there. The surface of the glass in your mask is potholed with microscopic depressions. Moisture is attracted to this uneven surface and adheres to the front causing the fogging. Decreasing the surface tension and creating a moisture film prevents fogging.
So how does Spit help? Saliva acts as a surfactant. Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading. The term surfactant is a blend of the words surface acting agent. As a surfactant; saliva decreases the surface tension of the droplets. The water from the condensation does not mound up as beads or droplets but, instead breaks to form bigger droplets that just roll away into the mask.
Ok so why use Spit? Well simply because it’s the most conveniently available surfactant and it works really well too. You could just as easily use shampoo, detergents, toothpastes, soaps, alcohols, or glycerin all used by divers as a spit alternative used to the same effect. You could also purchase manufactured defogging solutions. But spit is free, plentiful and doesn’t require a wetsuit with pockets to carry around!
Photographs by Many Cats 4 Me and rainspoo
