A coating composition comprises a dispersion of a film-forming resin in an aqueous medium including an aldehyde or a ketone and a component which contains solubilizing groups and has been made water-soluble or water-dispersible by treatment with a base, the base being liberated as free base during formation of a water-insoluble coating, the aldehyde or ketone being capable of reacting with free base to form a non-ionic compound, and the resin being incapable of modification by aldehyde or ketone under the conditions existing in the coating medium. The component made water-soluble or water-dispersible may be the film-forming resin or a dispersing or emulsifying resin for such resin. The base may consist of ammonia, primary, secondary, tertiary amines, hydroxylamine or its amine derivatives and compounds capable of reacting with such bases are formaldehyde, paraformaldehyde, acetaldehyde, or polymers thereof, glyoxal, chloral, acetophenone. The resin deposited e.g. a phenolic resin may react with the non-ionic product e.g. hexamethylene tetramine to effect cross-linking of the resin, and additional hexamethylene tetramine may be dissolved in the bath to maintain an increased concentration sufficient to complete the cross-linking. The film-forming resin may be natural or synthetic e.g. an ammonium salt of a polycarboxylic resin. In the examples, steel panels are coated by electrodeposition using a bath containing an aqueous solution of amine neutralized maleinized copolymer resin oil and (1) paraformaldehyde at an initial pH of 8.8 rising to 8.95, (2) formaldehyde at pH 9.0 rising to 9.05; steel panels are coated and form the anode in a bath of paint comprising a water dispersion of (4) a modified carboxylated oil, iron oxide pigment, talc, hexamethylene tetramine, formaldehyde at pH 7.0, (5) the resin of (1), carbon black, hexamethylene tetramine, paraformaldehyde at pH 9.0; in (6) a solution of a methacrylic acid - ethyl acrylate - 2 ethyl hexyl acrylate-styrene copolymer rendered soluble by the addition of ammonium hydroxide and containing formaldehyde is applied by spraying or electrodeposition at pH 9.7 to zinc; (7) steel panels are coated by electrodeposition using a bath comprising a phenolic-alkyd resin dispersion containing glyoxal; (8) a paint comprising a copolymer as in (6), zinc-coated rutile titanium dioxide, hexamethoxymethyl-melamine, formaldehyde is sprayed at pH 9.0 on to glass and baked; (9) mild steel panels are passed in succession through an electrodeposition bath having the composition described in (5) but omitting paraformaldehyde and replenished by the paint containing formaldehyde; (10) steel panels are coated in an electrodeposition bath comprising the composition described in (1), solid paraformaldehyde being present in the cathode compartment.ALSO:Coatings are produced by the application to the surface to be coated of an aqueous coating medium containing a film-forming resin capable of forming a coherent, paint-like or lacquer coating, such medium including a component which contains solubilizing groups and has been made water-soluble or water-dispersible by treatment with a base which is liberated as free base during formation of a water-insoluble coating of the resin on the surfaces, and an aldehyde or a ketone, or a compound containing an aldehyde group or a ketone group, capable of reacting with free base to form a non-ionic compound, the resin being incapable of modification by aldehyde or ketone under the conditions existing in the coating medium. The component made water-soluble or water dispersible may be the film forming resin or a dispersing or emulsifying resin for such resin. The surface may be of non-absorbent or absorbent materials such as paper, fabrics, non-woven fabrics. The coating can be produced by electro-deposition, and the effect of including an aldehyde or ketone is that pH value in the electro-deposition bath remains constant during coating and may be brought to any desired value. The base may consist of ammonia, primary, secondary, tertiary amines, hydroxylamine or its amine derivatives and compounds capable of reacting with such bases are formaldehyde, paraformaldehyde, acetaldehyde, or polymers thereof, glyoxal, chloral, acetophenone. The reactive substance e.g. formaldehyde may be added in solid, gaseous or aqueous form to the electro-deposition bath so as to be distributed throughout, or added to any liquid used to replenish the bath, or at any stage to reduce the pH as necessary, or to the cathode compartment, or the contents of the bath or cathode compartment may be circulated by pumping through say a tower in which a supply of formaldehyde is maintained. The resin deposited e.g. a phenolic resin may react with the non-ionic product e.g. hexamethylene tetramine to effect cross-linking of the resin, and additional hexamethylene tetramine may be dissolved in the bath to maintain an increased concentration sufficient to complete the cross-linking. The film-forming resin may be natural or synthetic e.g. an ammonium salt of a polycarboxylic resin. In the Examples, steel panels are coated by electro-deposition using a bath containing an aqueous solution of amine neutralised maleinized copolymer resin oil and (1) paraformaldehyde at an initial pH of 8.8 rising to 8.95, (2) formaldehyde at pH 9.0 rising to 9.05; steel panels are coated and form the anode in a bath of paint comprising a water dispersion of (4) a modified carboxylated oil, iron oxide pigment, talc, hexamethylene tetramine, formaldehyde at pH 7.0, (5) the resin of (1), carbon black, hexamethylene tetramine, paraformaldehyde at pH 9.0; in (6) a solution of a methacrylic acid-ethyl acrylate-2 ethyl hexyl acrylate-styrene copolymer rendered soluble by the addition of ammonium hydroxide and containing formaldehyde is applied by electro-deposition at pH 9.7 to zinc; (7) steel panels are coated by electro-deposition using a bath comprising a phenolic-alkyd resin dispersion containing glyoxal; (9) mild steel panels are passed in succession through an electro-deposition bath having the composition described in (5) but omitting paraformaldehyde and replenished by the paint containing formaldehyde; (10) steel panels are coated in an electro-deposition bath comprising the composition described in (1), solid paraformaldehyde being present in the cathode compartment.ALSO:Coatings are produced by the application to the surface to be coated of an aqueous coating medium containing a film-forming resin capable of forming a coherent, paint-like or lacquer coating, such medium including a component which contains solubilising groups and has been made water-soluble or water-dispersible by treatment with a base which is liberated as free base during formation of a water-insoluble coating of the resin on the surfaces, and an aldehyde or a ketone, or a compound containing an aldehyde group or a ketone group, capable of reacting with free base to form a non-ionic compound, the resin being incapable of modification by aldehyde or ketone under the conditions existing in the coating medium. The component made water-soluble or water dispersible may be the film forming resin or a dispersing or emulsifying resin for such resin. The surface may be of non-absorbent or absorbent materials such as paper, fabrics, non-woven fabrics. The coating can be produced by electro-deposition, and the effect of including an aldehyde or ketone is that pH value in the electrodeposition bath remains constant during coating and may be brought to any desired value. The base may consist of ammonia, primary, secondary, tertiary amines, hydroxylamine or its amine derivatives and compounds capable of reacting with such bases are formaldehyde, paraformaldehyde, acetaldehyde, or polymers thereof, glyoxal, chloral, acetophenone. The reactive substance, e.g. formaldehyde may be added in solid, gaseous or aqueous form to the electrodeposition bath so as to be distributed throughout, or added to any liquid used to replenish the bath, or at any stage to reduce the pH as necessary, or to the cathode compartment, or the contents of the bath or cathode compartment may be circulated by pumping through say a tower in which a supply of formaldehyde is maintained. The resin deposited, e.g. a phenolic resin may react with the non-ionic product, e.g. hexamethylene tetramine to effect cross-linking of the resin, and additional hexamethylene tetramine may be dissolved in the bath to maintain an increased concentration sufficient to complete the cross-linking. The film-forming resin may be natural or synthetic, e.g. an ammonium salt of a polycarboxylic resin. In the Examples, steel panels are coated by electrodeposition using a bath containing an aqueous solution of amine neutralised maleinised copolymer resin oil and (1) paraformaldehyde at an initial pH of 8.8 rising to 8.95, (2) formaldehyde at pH 9.0 rising to 9.05; steel panels are coated and form the anode in a bath of paint comprising a water dispersion of (4) a modified carboxylated oil, iron oxide pigment, talc, hexamethylene tetramine, formaldehyde at pH 7.0, (5) the resin of (1), carbon black, hexamethylene tetramine, paraformaldehyde at pH 9.0, in (6) a solution of a methacrylic acid-ethyl acrylate-2 ethyl hexyl acrylate-styrene copolymer rendered soluble by the addition of ammonium hydroxide and containing formaldehyde is applied by spraying or electrodeposition at pH 9.7 to zinc; (7) steel panels are coated by electrodeposition using a bath comprising a phenolic-alkyd resin dispersion containing glyoxal; (8) a paint comprising a copolymer as in (6), zinc-coated rutile titanium dioxide, hexamethoxy-methyl-melamine, formaldehyde is sprayed at pH 9.0 on to glass and baked; (9) mild steel panels are passed in succession through an electrodeposition bath having the composition described in (5) but omitting paraformaldehyde and