First, the color change after drying is carbon black, which can be brushed off with a brush. If there is still some scale, you can add a little vinegar to the kettle and remove it later.

Second, you can use toothpaste or detergent and other cleaning products containing friction agents to scrub.

It should be noted that before cleaning the kettle, it is best not to use the kettle, because the black is burnt metal residue, and the dispersed heavy metal content is high, which is harmful to human body.