We had purchased a Rohl Fire Clay kitchen sink 2-3 years ago that developed what looked to be hard water deposits along with normal stains. We tried sink a cleanser (Comet) and it did not remove the hard water deposits nor the stains very well. After calling the sink manufacturer, they asked if we had tried Astonish. We did not even know what Astonish was and looked it up on the Internet. We found it, ordered it and now the stains and deposits are gone. Would highly recommend this product for clay sinks.