Indigoid vat dyestuffs are obtained by condensing a 5 : 8 - dihalogen - 1 : 2 - naphththioindoxyl or a reactive a -derivative thereof with a component suitable for producing indigoid dyestuffs. The products may be treated with a halogenating agent such as bromine or sulphuryl chloride. The 5 : 8 - dihalogen - 1 : 2 - naphththioindoxy are more especially the 5 : 8-dibromo- and 5 : 8-dichloro-compounds and may be obtained from the corresponding dihalogen aminonaphthalenes by the known xanthate synthesis or from the sulphonic acid chlorides by way of the mercaptans, and can be converted into their reactive derivatives, e.g. their para-dimethylamino-anils, and may be used in this form for condensation with indigoid dyestuff components, e.g. thioindigoid or indole-indigoid dyestuff components, for example the para-dimethyl-amino anils of thionaphthene-quinone, of 5-methyl-6-chloro-thionaphthene-quinone, of 1 : 2-naphthtioisatin, of 1-chloro-2 : 3-naphththioisatin and of 6-ethoxy-thio-naphththene-quinone; the a -chlorides of isatin, of 4-methyl-7-methoxy isatin, of 4-methyl-5-chloro-7-methoxy isatin, of 5 : 7-dibromisatin and of 5-bromisatin; also 5 : 7-dibromisatin, 6-chloro-7-methyl-isatin, 5-bromisatin and acenaphthene-quinone. The condensation may be carried out at a raised temperature in an inert solvent such as chlorobenzene or glacial acetic acid. In many cases concentrated sulphuric acid may be used. The dyestuffs can be converted into leuco-ester salts, for example those of sulphuric acid and may be used in this form for dyeing or printing. The dyestuffs are especially suitable for printing cellulosic fibres such as cotton, linen and artificial silk or staple fibres of regenerated cellulose, preferably by the usual potassium carbonate printing process. In examples: 5 : 8 - dichloro - 1 : 2 - naphththioindoxyl is condensed by heating in the presence of glacial acetic acid with the 2-(41-dimethylamino)-anils of thionaphthene-quinone, of 4-methyl (or 5-methyl)-6-chloro-thionaphthene-quinone, of 6-ethoxy-thionaphthene-quinone or with acenaphthene-quinone itself with 1-chloro-2 : 3-naphththio-isatin (41 - dimethylamino) - anil, 5 : 7 - di - bromisatin, 5-bromisatin or 6-chloro-7-methylisatin; the 5 : 8-dichloro-1 : 2-naphththioindoxyl is also condensed in the presence of chlorobenzene with the a -chloride of 5 : 7-dibromisatin or of 5-bromisatin or 4-methyl-5-chloro-7-methoxy-isatin; also the a -(41-dimethylamino)-anil of 5 : 8-dichloro-1 : 2-naphththioindoxyl is heated in the presence of glacial acetic acid with 1 : 2-naphththioindoxyl; the dyestuff obtained from 5 : 8-dichloro-1 : 2-naphththioindoxyl and a -isatin chloride is introduced into nitrobenzene mixed with bromine and after standing is slowly heated to obtain a dyestuff practically identical with that obtained above from 5-bromisatin chloride; a mixture of p isatin, sulphuric acid monohydrate, ice and bromine is heated and after removing excess of bromine and hydrogen bromide the suspension is diluted with sulphuric acid monohydrate and heated with 5 : 8-dichloro-1 : 2-naphththioindoxyl to yield a dyestuff practically identical with that obtained on heating 5 : 8-dichloro-1 : 2-naphththioindoxyl with 5 : 7-dibromisatin as above; 5 : 8-dichloro-1 : 2-naphththioindoxyl is prepared by diazotising 5 : 8 - dichloro - 1 - naphthylamine hydrochloride, partly neutralizing with sodium carbonate and running into an aqueous solution of potassium xanthate. The xanthic ester formed is hydrolysed with alcohol and caustic potash and chloracetic acid rendered weakly alkaline with sodium carbonate is added. The potassium salt of the thioglycollic acid is precipitated and converted to 5 : 8-dichloronaphthalene-1-thioglycollic acid by adding hydrochloric acid. The latter is converted to the acid chloride by heating with phosphorus trichloride and tetrachlorethane and is then dropped into a suspension of aluminium chloride in tetrachloroethane, the whole poured on to ice and the lemon yellow indoxyl separated by filtration. Specification 233,831, [Class 2 (iii)], is referred to. The Specification as open to inspection under Sect. 91 includes the use of any dihalogen-naphththioindoxyl or a reactive derivative thereof, the following being specified: 4 : 8-dibromo (or dichloro)-1 : 2-naphththioindoxyl, 4 : 8- (or 5 : 8)-dichloro-2 : 1-naphththioindoxyl, 1 : 6-dichloro- or 1-bromo-6-chloro-2 : 3-naphththioindoxyl. Additional examples are given of the condensation of 5 : 8-dichloro-2 : 1-naphththioindoxyl with (1) the 21-(41-dimethylamino)-anil of thionaphthene - quinone; (2) with acenaphthene-quinone; (3) with the a -chloride of 5 : 7-dibromisatin prepared by heating the latter with phosphorus pentachloride and chlorobenzene; (4) with the a -chloride of 5-bromisatin; (5) with 5 : 7-dibromisatin, also of the condensation of 4 : 8-dichloro-2 : 1-naphththioindoxyl with 5 : 7-dibromisatin and with the a -(41-dimethylamino)-anil of 1-chloro-2 : 3-naphththioisatin, of 5 : 8-dibromo-2 : 1-naphththioindoxyl with 5 : 7-dibromisatin and with the 2-(41-dimethylamino)-anil of 4-methyl-6-chloro-thionaphthene-quinone; of 1-bromo-6-chloro-2 : 3-naphththioindoxyl with the 2-(41-dimethylanino)-anil of thionaphthene-quinone and with the a -chloride of 4-methyl-5-chloro-7-methoxy-isatin prepared by heating the latter with phosphorus pentachloride and chlorobenzene. An example is also given in which the dyestuff obtained from the condensation of 5 : 8-dichloro-1 : 2-naphththioindoxyl and 5 : 7-dibromisatin is pasted with water and vatted with sodium hydrosulphite after adding caustic soda solution, the stock vat being then added to a dye-bath of water, caustic soda solution and sodium hydrosulphite from which cotton is dyed fast blackish brown tints, 5 : 8- (and 4 : 8)-dichloro-2 : 1-naphththioindoxyl are prepared from 5 : 8-(or 4 : 8) - dichloro - b - naphthylamine by the xanthate method, in the case of the 5 : 8-dichloro compound, the 5 : 8-dichloronaphthalene-2-thioglycollic acid is converted into the acid chloride by treatment with phosphorus trichloride in chlorobenzene and the acid chloride is ring closed with aluminium chloride. 5 : 8-Dibromo - 2 : 1 - naphththioindoxyl is obtained by converting 5 : 8-dibromonaphthalene-2-sulphonic acid into the acid chloride by means of phosphorus pentachloride and reducing the acid chloride in known manner to the corresponding mercaptan which is condensed with chloracetic acid to form 5 : 8-dibromonaphthalene-2-thio-glycollic acid, the latter is converted to the acid chloride which is ring closed with aluminium chloride in chlorobenzene. 1-Bromo-6-chloro-2 : 3-naphththioindoxyl is obtained by treating 6 - chloronaphthalene - 2 - thioglycollic acid with bromine in carbon tetrachloride in the presence of anhydrous iron chloride to form 1 - bromo - 6 - chloro - naphthalene - 2 - thioglycollic acid which is converted into the acid chloride with phosphorus trichloride in chlorobenzene and the acid chloride is ring closed with aluminium chloride. This subject-matter does not appear in the Specification as accepted.ALSO:Indigoid vat dyestuffs are obtained by condensing a 5 : 8-dihalogen-1 : 2-naphththioindoxyl or a reactive a -derivative thereof with a component suitable for producing indigoid dyestuffs. The products may be treated with a halogenating agent such as bromine or sulphuryl chloride. The 5 : 8 dihalogen-1 : 2-naphthioindoxyls are more especially the 5 : 8 dibromo and 5 : 8 dichloro compounds and may be obtained from the corresponding dihalogen aminonaphthalenes by the known xanthate synthesis or from the sulphonic acid chlorides by way of the mercaptans, and can be converted into their reactive derivatives, e.g. their para-dimethylamino-anils, and may be used in this form for condensation with indigoid dyestuff components, e.g. thioindigoid or indole-indigoid dyestuff components, for example the para-dimethyl-amino anils of thio naphthene-quinone, of 5-methyl-6-chlorothionaphthene quinone, of 1 : 2-naphththioisatin, of 1-chloro-2 : 3-naphththioisatin, and of 6-ethoxy-thio-naphthene-quinone; the a -chlorides of isatin, of 4-methyl-7-methoxy-isatin, of 4-methyl-5-chloro-7-methoxy-isatin, of 5 : 7-dibromisatin, and of 5-bromisatin; also 5 : 7-dibromisatin, 6-chloro-7-methyl-isatin, 5-bromisatin and acenaphthene quinone. The condensation may be carried out at a raised temperature in an inert solvent such as chlorobenzene or glacial acetic acid. In many cases concentrated sulphuric acid may be used. The dyestuffs can be converted into leuco-ester salts for example those of sulphuric acid and may be used in this form for dyeing or printing. The dyestuffs are especially suitable for printing cellulosic fibres such as cotton, linen and artificial silk or staple fibres of regenerated cellulose, preferably by the usual potassium carbonate printing process. In examples: 5 : 8-dichloro-1 : 2-naphththioindoxyl is condensed by heating in the presence of glacial acetic acid with the 2-(41-dimethylamino)-anils of thionaphthene-quinone, of 4-methyl (or 5-methyl-)-6-chlorothionaphthene-quinone, of 6-ethoxy-thionaphthene-quinone or with acenaphthene quinone itself, with 1-chloro-2 : 3-naphththio-isatin (41-dimethylamino)-anil, 5 : 7-dibromisatin, 5-bromisatin or 6-chloro-7-methylisatin; the 5 : 8-dichloro-1 : 2-naphththioindoxyl is also condensed in the presence of chlorobenzene with the a -chloride of 5 : 7-dibromisatin or of 5-bromisatin or 4-methyl-5-chloro-7-methoxy-isatin; also the a -(41-dimethylamino)-anil of 5 : 8-dichloro-1 : 2-naphththioindoxyl is heated in the presence of glacial acetic acid with 1 : 2-naphthioindoxyl; the dyestuff obtained from 5 : 8-dichloro-1 : 2-naphththioindoxyl and a -isatin chloride is introduced into nitrobenzene mixed with bromine and after standing is slowly heated to obtain a dyestuff practically identical with that obtained above