Artificial fibres are impregnated with an aqueous preparation containing (1) an optical brightening agent having no brightening effect upon the fibre when applied by exhaustion of a dilute bath at elevated temperature, and (2) an artificial resin; they are then dried. The preparations may be applied at room or slightly elevated temperature by spraying or by treatment on the foulard. Fibres treated may be of cellulose triacetate, polyamides, polyurethanes, polyacrylonitrile or polyesters, e.g. of terephthalic acid and glycol, or of mixtures or copolymers of polycondensation or polymerization products, or mixtures of such artificial fibres or of artificial and natural fibres of animal or vegetable origin, e.g. in mixed yarns or mixed fabrics, may be treated. The preparations may contain dispersing or emulsifying agents. The optical brightening agent and resin may be selected so that one is basic and the other acidic. The many optical brightening agents specified include bisazole, dibenzazole, and azole compounds and derivatives; coumarin derivatives; stilbene derivatives which may not contain triazine rings; bisstyryl-benzene derivatives; benzidine sulphone derivatives; 1 : 2 : 3-triazole derivatives; pyrazoline derivatives; oxacyanine derivatives; oxdiazoles; imidazolones; dehydrocollidine derivatives and naphthalene-1 : 8-dicarboxylic acid imides. The many artificial resins specified include polyvinyl acetate; copolymers from isobutyl acrylate, acrylonitrile and acrylic acid; from n-butyl acrylate, vinyl acetate and acrylic acid; from the compound <FORM:0835719/IV(c)/1> and vinyl acetate or from these two components and n-butyl acrylate; condensation products of formaldehyde and urea, melamine, dicyandiamide, the reaction product of ethylene diamine dihydrochloride and dicyandiamide, acetoguanamine, acetoguanidine, biguanide, dicyandiamidine, ethylene dibiguanide, 1 : 3-propylene dibiguanide, 1 : 6-hexamethylene dibiguanide, 1 : 4 - cyclohexylene dibiguanide, melam, melem, ammeline, ammelide, 2-chloro-4 : 6 - diamino - 1 : 3 : 5 - triazine, benzoguanamine, acetoguanamine, formoguanamine, guanyl melamines, a mixture of methylol-melamine-methyl ethers or acetylene di-urea; and a condensation product (obtained step-wise) of stearic acid methylolamide, triethanolamine and methylol melamine methyl ether reacted with glacial acetic acid. The basic formaldehyde condensates may be used as salts with hydrochloric, sulphuric, formic, acetic, propionic or glycollic acid. Also included are copolymers of unsaturated acids containing hydrazide or hydrazide derivative groups with other unsaturated compounds and condensates of ethers of low M.W. aliphatic alcohols, e.g. methanol, with methylol-melamines.ALSO:Artificial textile fibres are treated with an aqueous composition which contains an optical brightening agent having no brightening effect upon the fibre when applied by exhaustion of a dilute bath at elevated temperature, and an artificial resin. Emulsifying or dispersing agents may be added. The optical brightening agents specified include bisazole, dibenzazole and azole compounds and derivatives; coumarin derivatives, stilbene derivatives which may or may not contain triazine rings; bis-styryl-benzene derivatives; benzidine sulphone derivatives; 1:2:3 triazole derivatives; pyrazoline derivatives; oxacyanine derivatives; oxdiazoles; imidazolones; dehydrocollidine derivatives and naphthalene-1:8-dicarboxylic acid imides. The resins specified include polyvinyl acetate; copolymers from isobutyl acrylate, acrylonitrile and acrylic acid; n-butyl acrylate, vinyl acetate and acrylic acid; the quaternary compound H2C = CHCONH(CH2)3N(CH2CONH) (C2H5)2(Cl) and vinyl acetate or these two components and n-butyl acrylate and copolymers of unsaturated acids containing hydrazide or hydrazide derivative groups with other unsaturated compounds. Also specified are condensation products of up to 4 mols. of formaldehyde with one mol. of urea, dicyandiamide, dicyandiamidine, guanidine, acetoguanidine, biguanide, ethylene biguanide, 1:3 - propylene dibiguanide, 1:6-hexamethylene dibiguanide, 1:4 cyclohexylene dibiguanide and their alkyl or hydroxyalkyl derivatives, organic nitrogen compounds produced by heating dicyandiamide with hydrochlorides or sulphates of aliphatic or cycloaliphatic amines containing at least 2 primary or secondary amino groups or chlorides of polyalkylene polyamines or of such polyamines as are obtained by reacting ethylene dihalides or glycerol dichlorohydrins with ammonia or alkanolamines, the condensates being obtained by reacting the components either alone or in the presence of a solvent or in the presence of caustic soda at 90 DEG to 95 DEG C. or in the presence of sulphuric or hydrochloric acid and acetic or formic acid under pressure at 80 DEG to 100 DEG C. A condensation resin specified is obtained by reacting 2 mols. of a non-cyclic compound containing at least once the group <FORM:0835719/IV (a)/1> in a first stage with 0.5 to 4 mols. of formaldehyde and 1 mol. of a salt of an aliphatic amine containing at least 2 primary or secondary amino groups, at above 100 DEG C., e.g. by reacting the organic nitrogen compounds at 150 DEG to 260 DEG C. and then condensing the product with paraformaldehyde at 170 DEG to 180 DEG C., or in the presence of a solvent at 110 DEG to 130 DEG C., and in a second stage condensing with 1 to 8 mols. of formaldehyde. Also specified are condensates of formaldehyde with melamine, melam, melem, ammeline, ammelide, 2-chloro-4:6-diamino-1:3:5 triazine, benzoguanamine, acetoguanamine formoguanamine, methylol melamine methylether, stearic acid methylolamide, tertiary amines containing a reactive hydrogen atom attached to an O or S atom, e.g. triethanolamine, guanylmelamines and mixtures thereof and substituted guanyl melamines. The condensates may be used as salts with hydrochloric, sulphuric, formic, acetic, propionic or glycollic acids. Other resins specified include reaction products of condensates of formaldehyde and aminotriazines or "urea compounds" which contain at least one methylol group etherified with a low molecular alcohol, nitriles or amides of unsaturated polymerizable acids and compounds with at least one active hydrogen atom which are capable of becoming attached to double bonds of the unsaturated compound. Examples are given.