Stove Glass gone black?

You may have noticed that an area of the glass in the stove door has gone cloudy, even after cleaning it does not wipe off.

Unfortunately there may be nothing that can be done, except for replacing the glass. However, the glass is not weakened and the stove can be used as normal, the damage is cosmetic.

The white cloudiness can be related to the presence of sulphur. All stove manufacturers give a very detailed list of acceptable fuels that can be used on their stoves. It is important that this is adhered to. The list can vary according to manufacturer, so one fuel that is suitable for one make of stove may not be suitable for another.

During lighting of a stove a small amount of condensation will build up on the surface of the glass, this is quite normal. If sulphur is present it will mix with the water and sulphuric acid will form. Sulphuric acid is corrosive. If left for any length of time it will start to etch into the surface of the ceramic glass. As the stove heats up the moisture boils away leaving a mixture of sulphur dioxide and sulphur trioxide which is a white powder. As it is contained in the etched areas, it cannot be cleaned off, resulting in the cloudiness. When the glass is wiped with a wet cloth, it will first look as though the cloudiness has gone. But, as soon as the glass has dried, the white powder, trapped in the etched glass appears again.

Here are ways in which you can avoid any discolouration of your stove glass:

• Regularly clean the glass. You can do this using something as simple as a damp cloth. Dip it in some clean ashes - make sure there are no bits of charcoal in the ash. When the stove is cool (and not running obviously!) use the cloth to wipe the inside of the glass in small circular motions. The ash acts as a gently abrasive and you should see the colouration coming off. When you're done finish off with a clean dry cloth. You can buy glass cleaner products but to be honest the ash on a rag trick nearly always sorts it.

• Most modern stoves are fitted with air-wash. Make sure that your stove is set correctly for the air wash to be operating. So if you're burning wood, when the stove is going well the bottom air control should be more or less shut and you then use the upper one to control the burn rate - this will help route more air to the top of the burning chamber and that will help keep the glass clearer.

• Do not let your stove 'slumber burn'. This means that you should avoid letting your stove tick over gently for overly long periods. When you first light the stove let it come up to temperature and let it burn hot for at least 20 minutes. If you have a multifuel stove that is designed to stay in overnight, make sure, after refuelling the stove before bed, that you open the vents and get the fire blazing, you can then close the vents and let the stove run slowly through the night. When you turn the stove down make sure that you're getting good flames still, with no darker whisps of smoke. If you want a stove to give out less heat then put a little less wood on rather than turning it right down.

• Use well seasoned wood. Burning wet wood is a sure way to blacken the glass and you'll also get little heat. Woodsure Ready to burn certified firewood is a way to be sure that it's properly dry.

• Having a nice hot fire every so often will also burn off some of the deposits. Make sure that your chimney is kept well swept and you should be good to go.