Scraping old paint off window glass
Don't try and do it with just the razor blade in your hand - it is not only dangerous - you can't get a good angle on the blade.
Remember to wear gloves and glass (razor blades sometime snap off and the pieces fly)
This has always worked for me - and I have scaped a window or two in my day...
You can also take a rag and dappen the window where you want to scrape with goof-off
this will soften the aged paint for you so you don't have to use more muscle.