If you have not figured out that you NEED clay for proper car care, you won't' have any idea why you should pay for this stuff. Realistically, you can use any fine-grit clay, but this stuff is nice and soft, and if you use it right, it'll be SO worth it Clean windshield first. Use soap, Windex, whatever. Then make a hand-sized thin piece of this and wipe it over the entire windshield, while keeping a low flow of water on it constantly. You NEVER want high friction, but don't believe the hype that you have to waste exterior detailer spray doing this. Water works fine. Once you've gone over the entire windshield, dry completely and apply (yes, I'm gonna pimp something else Amazon sells) Rain-X as directed. Original Rain-X, NOT the "cleaner/protector" stuff. The Rain-X will last about twice as long, and water will just fall off of your windshield. Do this and you will almost never need your wipers, which is actually a good safety practice. Losing a wiper motor without treating your windshield means you're stuck until the rain ends. Clean, clay, and treat your windshield, and just don't worry about it. Then clay the rest of your car using clay for paint. Amazon sells lots of it, and I'm not going to argue which is best. But if you don't clay your car once a year, you'll never get that shine you saw when you bought it again.. But I digress. This stuff rocks just like anything else I've ever bought from Griot's. Go get some.

BTW, if Amazon lets me get away with the headline, it's a direct homage to Blazing Saddles. If you didn't realize that, stop, go watch that movie, then come back and order some of this blue stuff.

I used this to clean the back window of my 2008 Corvette. The Corvette back window is fairly horizontal and water gathers easily to leave monster water spots. I had over 9 years worth of buildup and on a sunny day, it was difficult to see out of the back window.

Griots glass clay is the only thing I found that worked when removing these water spots. I used a mixture of dish soap and distilled water in a spray bottle as lubricant and worked the window in sections. Each section for some round motion followed by an up and down motion and a side-to-side motion. Be generous with the lubricant.

I regularly folded the clay back over on itself.

In all, the large window took about 1 hour to clean. When done, it had a mirror finish. I can't see any water spots. I'm amazed. I had already tried vinegar water, barkeeps friend, and even gentle scraping with a razor blade and none of them made a difference.

As for people complaining of the size: the clay was just the right size if you ask me. It fit comfortably in my hand. And the package really isn't oversized because I put the clay in quart ziploc and had to squish it to fit back in the container. A smaller container wouldn't have held it.

I would have never thought that a clay for glass would work. I bought this based on using other Griot products, that were superior and hope this would be too. OK, it is well worth it. You all use clay bars on paint jobs, and it would be get the junk out of paint. This gets the gunk out of your windshield. Makes the windshield closer to new. Follow up with Griot's glass cleaner and glass is better than its been in a long time. There is something different about this clay versus the clay used on paint jobs; clay bars aren't interchangeable. Kind of pricy, but worth it.

It worked. A safety razor blade worked better to remove accumulated mineral deposits on the windows. I'll still have to buff the glass, but this did seem to work some. I'm not sure I know how to effectively use it. Other clays have worked better on painted surfaces so I thought to try this on glass . . . and the razor blade and vinegar work better.

I never used clay before and I'm kicking myself for not knowing about this sooner. I use the clay to prep the windshield for Rain-X and it makes a huge difference. you can clean you windshield all you want, you will still feel a noticeable difference after using the clay: It makes it silky smooth.

I wipe the windshield down using Invisible Glass and then wet it again with the same. I use the clay horizontally and then vertically and then wipe clean. I usually apply Rain-X next. but even when I don't, I could still see a big improvement in shedding water.

Ever see the grim build up where your windshield wipers stop? especially when you get stuck behind a diesel in the rain, the clay pulls that right off.