It is not hard to make. The idea is based on my experience with a ceramic coffee cup that started to sing (make noise) one morning. It sang ever morning when it was filled with hot coffee. The singing lasted nearly a minute.

Upon inspection, I discovered that the cup had a microscopic crack through the ceramic covering, perhaps leading to the porus clay within the ceramic covering.

I think it works like this when hot coffee is poured into the cup, air expands from the pourous clay to excape through the crack. If the crack is just the right thickness excaping air flowing through crack will create tone..

To keep it going the next day I think it is important to dry the cup before it cools so the clay will refill with air instead of coffee.

Remarkable, I didn't dry it before it cooled down. After washing, the clay dried on its own. I used the cup for weeks until the wife convinced me that I deserve to drink coffee in the morning from an unbroken cup in silence.

Alas, my wife finds joy in perfection, a quality that I am often reminded to strive for.

el dueno