Before doing this, you should note the following:
For safe household use, you should only use ashes that are free of heavy metals. It is therefore particularly important to use natural and untreated fuel. Charcoal and barbecue briquettes, for example, are not suitable because they contain heavy metals such as chromium and harmful phosphates.
Fuels containing mineral oil, such as printed newspapers, should also be avoided. Also, always wear gloves when handling ashes, as the high pH of ashes can damage your skin.