Prevent Bathroom Mirror Fogging with Soap

In summary, when you take a shower the bathroom mirror fogs. Rubbing a thin layer of soap on the mirror and then gently rubbing it in with a cloth helps to prevent the mirror from fogging.
  • #1
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Whenever you take a shower the bathroom mirror fogs. I discovered if one rubs a thin layer of soap on the mirror, then gently rubs it in with a cloth, the mirror does not fog. I could not think of any other reason other than some chemical reason. Why does this happen?
 
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  • #2
Fog is actually millions of little water beads. Soap reduces surface tension between water and glass causing the water to sleet rather than bead. The water is still there; it's just more together.
 
  • #3
ShawnD said:
Fog is actually millions of little water beads. Soap reduces surface tension between water and glass causing the water to sleet rather than bead. The water is still there; it's just more together.
I think you meant to say 'adhesion', rather than 'surface tension'.
 
  • #4
Soap will indeed reduce the surface tension of the beads of water, thus making the wetting angle of the droplets much smaller, and tending to allow them to form a film rather than collection of droplets.
 
  • #5
So does the water just sheet off the water?
 
  • #6
Yeah pretty much. The same thing will happen after you wash your car.
Pay attention to how water sits on the hood of your car:
-before you wash it
-after you wash it (with soap)
-after you wax it

Before you wash it, water will sort of stay on and sort of fall off the hood. Cohesion and adhesion are not too different.
After you wash with soap, water will just slide off the hood. Adhesion is much stronger than normal.
After you wax, water will form little beads. Cohesion is much stronger than normal.

That beading effect is why I will never wax my car. If your car is left out when it rains, rain water (which is far from clean) will bead all over the car. With cohesion being so strong, there is a lot of added friction between water and your car, so that water just stays there. The water eventually evaporates after the rain has stopped, and the crud that was in the rain water is now all over your car in the form of brown dots. Your car looks like crap after that, and it's incredibly difficult to clean.
 
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  • #7
brewnog said:
Soap will indeed reduce the surface tension of the beads of water, thus making the wetting angle of the droplets much smaller, and tending to allow them to form a film rather than collection of droplets.
This is true. The soap molecules (stearates I guess) will reduce the surface tension of water. I was a bit confused by the "between water and glass" bit.
 
  • #8
I use rain-x no fog{for cars} for my indoor mirrors, it works for a really long time with one application without the haze that soap can leave.
 
  • #9
hypatia said:
I use rain-x no fog{for cars} for my indoor mirrors, it works for a really long time with one application without the haze that soap can leave.

Onion or Potato juice also does the same thing.
 
  • #10
Onion or Potato juice also does the same thing

But I would'nt want the smell of onion, or any food that might attract bugs.
When I dive I spit into my facemask to keep it from fogging. But I can't get myself to stand and spit on my mirror..lol
 

What causes bathroom mirror fogging?

Fogging on a bathroom mirror is caused by condensation. When warm, moist air comes into contact with a cool surface, it turns into water droplets, causing the surface to fog up.

How does soap prevent bathroom mirror fogging?

Soap works as a surfactant, which means it reduces the surface tension of water. When applied to a mirror, it creates a thin film that prevents water droplets from forming, thereby preventing fogging.

Is soap the only way to prevent bathroom mirror fogging?

No, there are other methods to prevent bathroom mirror fogging, such as using a defogging spray or installing a heated mirror. However, soap is a simple and cost-effective solution that is readily available in most households.

Can any soap be used to prevent bathroom mirror fogging?

Any type of soap, whether liquid or bar, can be used to prevent bathroom mirror fogging. However, soaps with a higher concentration of fatty acids, such as dish soap and shampoo, tend to be more effective.

How often should soap be applied to prevent bathroom mirror fogging?

The duration of fog prevention depends on factors such as the humidity in the bathroom and the type of soap used. In general, soap should be reapplied every 1-2 weeks for optimal results.

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