in the formation of a metal or metal compound coating on a face of a heated glass substrate during its forward displacement by contacting such face at a coating station with at least one stream of droplets comprising one or more substances from which the coating is formed , problems are encountered in controlling the thickness of the coating . to facilitate such control , the or each droplet stream is downwardly inclined towards the substrate in the forward direction or in a rearward direction , and at least one current of preheated gas is discharged into the environment above the substrate to flow in the same forward or rearward direction as the droplet stream and into contact therewith , the preheated gas current temperature being such as to influence the temperature of the droplets on their way to the substrate . the invention includes apparatus for performing the method .