Washing away fireplace smoke and soot, or cleaning the smoke off the glass in wood stove doors, is easy and safe using washing soda (available in the laundry section of the supermarket).
Washing soda is one of the best heavy duty cleaners I know, and an excellent substitute for powerful solvents.
Washing soda can peel wax off floors, and it isn’t recommended for aluminum, so only use on surfaces such as unpainted wood, glass or stone, that won’t be harmed.
1 bucket warm water
1/2 cup washing soda
Wash surface, wearing gloves; then rinse.
For really tough jobs, make a thick washing soda paste by mixing it with water, and then spread the paste on the soot. Keep the paste damp by spraying every hour or so with a spray bottle. Leave the paste on overnight, and then rinse. Make certain to only use this formula on inert surfaces such as glass and stone, as this amount of washing soda can peel off paint, wax, etc.