A white material appeared from time to time on the top surface of ceramic floor tiles which was difficult to clean off.  This caused the installer greatly increased tile installation costs. We were asked to identify the white material so that the installer might either get the tile supplier to remove it prior to shipment or that the installer would know better how to remove it.

We examined the material with FTIR and determined that it was not organic and likely had magnesium and silicon oxides in it.  We then analyzed it with XPS and compared the results to similar analysis of white material from the bottom side of the tile and from an area on the top side of the tile which was not covered with the white material.  The white material on the top surface was found to be rich in magnesium oxide and a match with the much larger quantities of white material on the bottom side of the tile.  The top surfaces were becoming dirty because the bottom surfaces were dirty.  The magnesium-rich white powder may have come from refractory bricks, which are easily eroded.

The report is here: XPS of White Material on Tile