As far as I know, that’s pre-Tang and one of the methods of making tea during the Tang, but Lu Yu already speaks against it in his Chajing. He doesn’t mind adding a bit of salt, though.Tead Off wrote:From what I've read, it was more than tea that they put into their tea bowls. Other things would make their way into the brew.

By the Song dynasty, from which Jian ware bowls (»Tenmoku«) come, powdered tea (without supplements) was whipped to a froth with a tea whisk (»whipped tea«), a tradition the Japanese imported along with Chan (Zen).