An article has affixed to a surface thereof or to part of a surface, a coating which comprises an essentially continuous water-insoluble matrix of binder material having distributed throughout its entire volume multitudinous air-binder interfaces, substantially all of which have maximum dimensions between one half and one micron, so that the interfaces scatter light and make the coating opaque. The matrix is a dried uncollapsed residue of an oil-in-water emulsion in which the aqueous phase contains the binder material. If the binder is originally water-soluble it is rendered insoluble during the formation of the emulsion or after deposition of the coating. The discontinuous phase may be an organic liquid that is not a solvent for the binder, is not miscible with water, and has a boiling point higher than that of water. It may contain in solution a transparentizing agent. The coated article may be sensitive to the local application of pressure, which causes local transparentization of the coating. Binders referred to are: casein, bentonite, polyvinyl alcohol, methylcellulose, alphaprotein, animal glue, modified starches, sodium silicate, shellac, natural rubber and synthetic rubbers such as copolymers of butadiene with acrylonitrile or styrene. The natural and synthetic rubbers should preferably be used with a small proportion of non-elastic binder. Casein and alpha-protein are brought into solution with the aid of an alkaline solubilizing agent such as ammonia, sodium hydroxide, borax, sodium carbonate or tri-sodium phosphate. Casein, alpha-protein and glue may be insolubilized by reaction with a salt of copper, aluminium or chromium, or with an aldehyde. Transparentizing agents referred to are: paraffin wax, stearic acid, liquid polyamide, polyester, butadieneacrylonitrile copolymer, a silicone fluid, mineral oil, lanolin, blown soya bean oil, stearamide wax, polyethylene, polyglycol, glyceryl monostearate, petrolatum and oxidized microcrystalline wax. The emulsifying agent, if required, may be of soap, e.g. sodium or ammonium stearate, palmitate or laurate. Liquids referred to for the discontinuous phase are: xylene, kerosone, mineral spirits, high-flash naphthas, butyl methyl ketone, amyl ethyl ketone, octane, butyl acetate and amyl acetate. The coating may be coloured by adding a dye to the emulsion. Reference has been directed by the Comptroller to Specification 705,417.ALSO:An article, e.g. a sheet of paper, a board, or a wall, has affixed to a surface thereof or to part of a surface, a coating which comprises an essentially continuous water-insoluble matrix of binder material having distributed throughout its entire volume multitudinous air-binder interfaces, substantially all of which have maximum dimensions between one half and one micron, so that the interfaces scatter light and make the coating opaque. The matrix is a dried uncollapsed residue of an oil-in-water emulsion in which the aqueous phase contains the binder material. If the binder is originally water-soluble it is rendered insoluble during the formation of the emulsion or after deposition of the coating. The discontinuous phase may be an organic liquid that is not a solvent for the binder, is not miscible with water, and has a boiling point higher than that of water. It may contain in solution a transparentizing agent. The coated article may be sensitive to the local application of pressure, which causes local transparentization of the coating. Binders referred to are: casein, bentonite, polyvinyl alcohol, methylcellulose, alphaprotein, animal glue, modified starches, sodium silicate, shellac, natural rubber and synthetic rubbers such as copolymers of butadiene with acrylonitrile or styrene. The natural and synthetic rubbers should preferably be used with a small proportion of non-elastic binder. Casein and alpha-protein are brought into solution with the aid of an alkaline solubilizing agent such as ammonia, sodium hydroxide, borax, sodium carbonate or tri-sodium phosphate. Casein, alpha-protein and glue may be insolubilized by reaction with a salt of copper, aluminium or chromium, or with an aldehyde. Transparentizing agents referred to are: paraffin wax, stearic acid, liquid polyamide, polyester, butadieneacrylonitrile copolymer, a silicone fluid, mineral oil, lanolin, blown soya bean oil, stearamide wax, polyethylene, polyglycol, glyceryl monostearate, petrolatum and oxidized microcrystalline wax. The emulsifying agent, if required, may be a soap, e.g. sodium or ammonium stearate, palmitate or laurate. Liquids referred to for the discontinuous phase are: xylene, kerosene, mineral spirits, high-flash naphthas, butyl methyl ketone, amyl ethyl ketone, octane, butyl acetate and amyl acetate. The coating may be coloured by adding a dye to the emulsion. Reference has been directed by the Comptroller to Specification 705,417.ALSO:An article, e.g. a sheet of paper, a board, or a wall, has affixed to a surface thereof or to part of a surface, a coating which comprises an essentially continuous water-insoluble matrix of binder material having distributed throughout its entire volume multitudinous air-binder interfaces, substantially all of which have maximum dimensions between one-half and one micron, so that the interfaces scatter light and make the coating opaque. The matrix is a dried uncollapsed residue of an oil-in-water emulsion in which the aqueous phase contains the binder material. If the binder is originally water-soluble it is rendered insoluble during the formation of the emulsion or after deposition of the coating. The discontinuous phase may be an organic liquid that is not a solvent for the binder, is not miscible with water, and has a boiling point higher than that of water. It may contain in solution a transparentizing agent. The coated article may be sensitive to the local application of pressure, which causes local transparentization of the coating. Binders referred to are: casein, bentonite, polyvinyl alcohol, methylcellulose, alpha-protein, animal glue, modified starches, sodium silicate, shellac, natural rubber and synthetic rubbers such as copolymers of butadiene with acrylonitrile or styrene. The natural and synthetic rubbers should preferably be used with a small proportion of non-elastic binder. Casein and alpha-protein are brought into solution with the aid of an alkaline solubilizing agent such as ammonia, sodium hydroxide, borax, sodium carbonate or tri-sodium phosphate. Casein, alpha-protein and glue may be insolubilized by reaction with a salt of copper, aluminium or chromium, or with an aldehyde. Transparentizing agents referred to are: paraffin wax, stearic acid, liquid polyamide, polyester, butadiene-acrylonitrile copolymer, a silicone fluid, mineral oil, lanolin, blown soya bean oil, stearamide wax, polyethylene, polyglycol, glycerol monostearate, petrolatum and oxidized microcrystalline wax. The emulsifying agent, if required, may be of soap, e.g. sodium or ammonium stearate, palmitate or laurate. Liquids referred to for the discontinuous phase are: xylene, kerosene, mineral spirits, high-flash naphthas, butyl methyl ketone, amyl ethyl ketone, octane, butyl acetate and amyl acetate. The coating may be coloured by adding a dye to the emulsion. A thin overcoat, e.g. of polystyrene, may be applied over the coating of the invention. Marking tapes may be made by coating a flexible backing with a pressure-sensitive coating of the invention on one side, and an adhesive on the other. Reference has been directed by the Comptroller to Specification 705,417.ALSO:An article, e.g. a sheet of paper, has affixed to a surface thereof or to part of a surface, a coating which is pressure-sensitive and comprises an essentially continuous water-insoluble matrix of binder material having distributed throughout its entire volume multitudinous air-binder interfaces, subsequentially all of which have maximum dimensions between one half and one micron, so that the interfaces scatter light and make the coating opaque. The matrix is a dried uncollapsed residue of an oil-in-water emulsion in which the aqueous phase contains the binder material. If the binder is originally water-soluble it is rendered insoluble during the formation of the emulsion or after deposition of the coating. The discontinuous phase may be an organic liquid that is not a solvent for the binder, is not miscible with water, and has a boiling point higher than that of water. It may contain in solution a transparentizing agent. The local application of pressure causes local transparentization of the coating. If the backing is coloured tissue paper or synthetic resin film, the colour will show through the transparent area and so produce a visible mark. Copies can be made by superposing several such sheets with a sheet of plain paper on top, and writing or typing on the top sheet. These copies can be fixed by subsequent heating to a temperature below that at which the coating flows. Binders referred to are: casein, bentonite, polyvinyl alcohol, methylcellulose, alphaprotein, animal glue, modified starches, sodium silicate, shellac, natural rubber and synthetic rubbers such as copolymers of butadiene with acrylonitrile or styrene. The natural and synthetic rubbers should preferably be used with a small proportion of nonelastic binder. Casein and alpha-protein are brought into solution with the aid of an alkaline solubilizing agent such as ammonia, sodium hydroxide, borax, sodium carbonate or tri-sodium phosphate. Casein, alpha-protein and glue may be insolubilized by reaction with a salt of copper, aluminium or chromium, or with an aldehyde. Transparentizing agents referred to are: paraffin wax, stearic acid, liquid polyamide, polyester, butadiene-acrylonitrile copolymer, a silicone fluid, mineral oil, lanolin, blown soya bean oil, stearamide wax, polyethylene