What is the origin of the idiom "dumb as a coal bucket" and when to use it?

The exact origin of the phrase "dumb as a coal bucket" is unclear. It is likely a variation or adaptation of the more commonly known phrase "dumb as a box of rocks," which has been in use since at least the mid-20th century. Both phrases share the same meaning, implying a lack of intelligence or mental acuity. This phrase is primarily used in informal or colloquial contexts and is not considered a widely recognized idiom.