Mix two parts rubbing alcohol with one part water in a spray bottle. Spray your windshield. The ice melts in seconds.

I learned this the hard way — standing in a Michigan parking lot at 6 AM, scraping furiously while my fingers went numb inside gloves that were not warm enough. A guy in the next car over sprayed his windshield, waited about ten seconds, and wiped it clean with his wipers. I was still scraping.

Why rubbing alcohol works

Rubbing alcohol — isopropyl alcohol — has a freezing point of -128°F. It does not freeze in any weather you will ever drive in. When you spray it on ice, the alcohol lowers the freezing point of the water at the surface, and the ice melts almost instantly.

Water alone freezes at 32°F. The alcohol-water mixture stays liquid far below that. You are basically pouring liquid anti-freeze onto your windshield.

How to make the spray

Get a spray bottle. Fill it two-thirds full with 70% isopropyl rubbing alcohol — the kind in the first-aid aisle at any drugstore. Fill the remaining third with water. Add a drop of dish soap if you want — it helps the mixture cling to vertical surfaces.

Shake to mix. Keep the bottle in your car, not in the house — the whole point is having it ready when you walk outside to a frosted windshield.

Do not use 91% alcohol undiluted. It evaporates too fast to work well. The water in the mixture slows the evaporation enough for the alcohol to do its job.

How to use it

Spray a generous layer onto the frosted or iced windshield. Wait ten to fifteen seconds. You will see the frost start to dissolve. Turn on your wipers and the slush wipes away.

For thick ice — the kind that requires chipping — spray, wait thirty seconds, then use your scraper. The ice will come off in sheets instead of flakes because the alcohol has weakened its grip on the glass.

What not to do

Do not pour hot water on a frozen windshield. I know people who have done this. The temperature shock can crack the glass. It happens fast and it is expensive.

Do not use vinegar. It does not work nearly as well and the smell lingers in your car for days.

Do not leave the spray bottle in direct summer sun inside your car. Alcohol expands with heat and the bottle can leak. Store it under a seat or in the trunk when not in use.

This spray has saved me at least five minutes every frozen morning. Over a Michigan winter, that adds up to hours of not scraping.