Abstract: A magnetic recording medium is disclosed, which is formed by providing on a non-magnetic support, a lower layer comprising at least one of a ferromagnetic powder and a non-magnetic powder dispersed in a binder, and providing on the lower layer while the lower layer is in a wet condition, an upper magnetic layer comprising a ferromagnetic powder dispersed in a binder, wherein the upper magnetic layer has a dry thickness of 1.0 .mu.m or less, and the non-magnetic support is a multi-layer structural support comprising at least an uppermost support layer and a lowermost support layer, wherein the uppermost support layer is coated with the lower non-magnetic or magnetic layer, each of the uppermost layer and the lowermost layer comprises a biaxially oriented film comprising a thermoplastic resin containing filler particles, and the uppermost support layer has a center line average surface roughness Ra in the range defined by the following formula:Ra(Cut off: 0.25 mm)-Ra(Cut off: 0.08 mm).ltoreq.10 nm.

Abstract: A process for the preparation of a magnetic recording disk comprises the steps of providing a magnetic recording layer on a surface of a nonmagnetic support, punching the nonmagnetic support together with the magnetic recording layer into a disk having a circular hole in its central portion, and fitting mechanical members including a center core made of a synthetic resin into the hole of the support. The nonmagnetic support having the magnetic recording layer and at least the center core of the mechanical members are subjected to heat treatment independently prior to fitting the mechanical members including the center core into the hole of the support.

Abstract: A magnetic recording medium which comprises a non-magnetic support having thereon a magnetic recording layer comprising ferromagnetic particles dispersed in a binder, with the magnetic layer further containing an organoaluminum compound or with the surface of the ferromagnetic particles being treated with an organoaluminum compound.

Abstract: A method for coloring a stainless steel using a potential-time curve which comprises seeking for an individual coloring potential difference to be colored by compensating a standard coloring potential difference by difference between a standard inflexion point potential and an individual inflexion point potential, and stopping the coloring when the individual coloring potential changes in an amount corresponding to the individual coloring potential difference from the individual inflexion point potential.