Soot build-up is inevitable when you burn wood in your fireplace, as the smoke settles onto the glass and leaves your doors with a thick layer of dark film. When you're constantly burning wood in the fireplace, stay away from any type of chemically-based or flammable cleaning product, as this can create a very dangerous situation. Use a natural cleaning element that removes all of the soot without use of dangerous ingredients.
Saturate a handful of paper towels with white vinegar.
Scrub the paper towels over your fireplace glass, using new paper towels as needed until all soot is removed.
Lightly drizzle a clean paper towel with just a few drops of the white vinegar and give one final cleaning to both sides of the glass. Allow to air dry, and you are left with clean fireplace glass that is free of soot and streaks.
Heavy gunk on glass doors can be scraped off with a razor blade.