How Do 'Fogless' Shower Mirrors Work?

[Surreal]

I bought one of these things so I could shave in the shower, but I don't understand what's preventing it from fogging up. The shower door fogs up, the other mirror fogs up, but this mirror does not. How does it work? Why don't they use this technology on automobiles??

Thanks.

[kferr]

I don't know if this is true for yours, but some types of shower mirrors mount between the pipe and the shower head so that the hot water flows thru it. The water heats the mirror which prevents condensation.

[Surreal]

This one is not that complicated. No hot water is channeled through it. It's just a small mirror that cost $5.

I couldn't find anything about it at howstuffworks.com either.

[dantheman]

Funny, I was just thinking about this. Here's a wrinkle for your question, though. I've gone through several of these so-called fogless mirrors. They're fogless for a while (say a few months), and next thing you know, they're fogging up every day. Fogless, my tuckus.

[ftg]

I don't know if most work this way...

"Fog" on glass is caused by droplets of water sticking to the mirror and remaining drops. This has to do with the tiny crevices that even glass has. If the mirror is coated with a ultra-thin layer of a lighweight oil, the drops "spread out", merge and thus form a more or less uniform layer. Hence, a clearer image.

Commerical products such as "Rain-X" do this for car windows and for larger drops. However, I have found a tiny amount of "Armor-all" type products to work just as well in that application. Repeat, tiny.

[NurseCarmen]

Yep, a thin layer of oil keeps em fogless, and thin layer wears out pretty quick. I've found rubbing some shaving cream on them rejuvinates them for a short while. Rain-X would work better, but I'm usually unwilling to walk to my garage naked and wet. The shaving cream is right there.

[dantheman]

Yeah, but if you rub shaving cream on the mirror, how are you gonna see? :)

[xash]

Originally posted by dantheman
Funny, I was just thinking about this. Here's a wrinkle for your question, though. I've gone through several of these so-called fogless mirrors. They're fogless for a while (say a few months), and next thing you know, they're fogging up every day. Fogless, my tuckus.

my spectacles have this fogless option built into the lenses. i think i remember the guy selling it to me saying that it's a property that is built into the plastic lens ( as opposed to a film on top of the lens).

it used to work like a beaut initially, but after some months it doesn't clear out as fast as it used to (in the same circumstances). most useful when i get out of a/c cars and step into the hot outdoors.

[Squink]

The surface of a fogless mirror is treated with a silicon compound that reacts with water loving hydroxyl groups, and replaces them with hydrophobic silicon compounds. Over time, the glass weathers and produces more surface hydroxyls that fog can form around.

[dantheman]

Well, then they should be "temporarily fogless mirrors"!

[NurseCarmen]

Originally posted by dantheman
Well, then they should be "temporarily fogless mirrors"!

I haven't the foggiest.