Exactly....! BUT...unless you seriously know what your doing,DONT Put a Razor Blade to ANY Glass.
I owned a large Window Cleaning Business for 32 years and can say I've seen 10's of thousands of $$ in damage from people trying to use a razor blade on glass.Todays glass is way more complicated that the old stuff with coatings,tempered,etc...they have written books on the subject.BUT if you must use,as Wheelman said....WITH LUBRICANT...and you might do OK...WITHOUT...I can almost guarantee when the sun shines,you will see all the scratches..