A method for treating a substrate is disclosed in which a propellant stream is passed through a channel and directed toward a substrate. Substrate pre-marking or post-marking treatment material is controllably introduced into the propellant stream and imparted with sufficient kinetic energy thereby to be made incident upon a substrate. A multiplicity of channels for directing the propellant and treatment material allow for high throughput, high resolution in-situ treatment. Marking materials and treatment materials may be introduced into the channel and mixed therein prior to being made incident on the substrate, or mixed or superimposed on the substrate without registration. One example is a single-pass, full-color printer.