Ink jet printing is continuing to move into commercially attractive but technically demanding markets, such as the marking and decoration of glass, ceramics and metals. These markets can require inks with exceptional weather fastness, very high temperature resistance or chemical resistance. The organic pigments and binders commonly used in existing ink jet inks are not sufficiently resistant for such applications. There is therefore a need for jet inks based on stable dispersions of dense inorganic pigments and powdered glass frits. Such inks require a new understanding of jet ink formulation. This paper reviews some of the requirements and looks at how the problems are being resolved to make these emerging applications feasible.