A low reflectivity coating (20) is formed of a layer of carbon nanostructures (20) over a contact surface (14) of a substrate (10), from a spray incorporating the carbon nanostructures in suspension in a solvent. The carbon nanostructure layer provides a very low reflectivity coating which may be further enhanced by etching the outer surface of the coating. The layer may be etched for reduced reflectivity. Very low reflectivity coatings have been achieved.