Chromium mordants in cotton dyeing.

The Textile Mercury, 13.12.1890

The bichromates of potash and soda are used to a large extent in dyeing cotton aniline black and chrome yellows and oranges. The dyeing of aniline black on cotton consumes large quantities of the bichromates if ungreenable blacks are to be produced. In dyeing of logwood blacks and cutch browns it is largely need. So far no method is known of mordanting cotton with chrome mordants in a perfectly satisfactory manner. In the cases of the use of chromes given above, these bodies are used either in the dye-bath or afterwards to fix the colour on the fibre.

For such colours as galloflavine, anthracene brown, gambine dioxine, which require the fibre to be previously mordanted, no chrome mordant has been found that will give full rich colours with these dye-stuffs; either there is not a sufficient qnantity of mordant fixed on the fibre or the mordant is not uniformily distributed on the fibre, and uneven colours result. The employment of basic mordants with or without the use of glycerine to prevent too rapid drying gives only imperfect results. A method of inordanting sensibly superior to that ordinarily used consists in fixing on by the other of a salt of chromium and an alkaline solution of oxide of chromium; a double precipitation of oxide of chrome occurs, which is derived partly front the salt of chrome and partly from the fixing bath. This gives very uniform and full shades more en than any other method of using chrome mordants. The basic mordant must contain a slight excess of oxide of chromium; if the caustic soda be in excess the results are not as good, as the alkali prevents the proper fixation of the chrome oxide. For light colours a bath of basic mordant may be used, the fibre being laid down in it over night, then wrung, dried, and washed. Treatment with silicate of soda or ammonia will help to fix the oxide of chrome on the fibre.

It has also been proposed that for colours where a light shade of grey will not have any apprepable effect, the cotton be dyed a light grey with bichromate, aniline acid and then dye in the colouring matter as usual. There is some quantity of oxide of chrome deposited on the fibre, and this acts as a mordant.