PAINTS, DYES, AND VARNISHES 



tion as dyes differs from their use as paints and stains, 

 their composition is identical. 



Without regard to the natural scientific grouping of 

 artificial colors, the dyer divides them into six or more 

 groups based upon their practical application. A recent 

 grouping by Farrell is as follows: 



1. Direct or substantive cotton dyestuffs 



2. Acid dyestuffs 



3. Basic or tannic-acid dyestuffs 



4. Mordant dyestuffs 



5. Vat dyestuffs 



6. Developed dyes 



The first of these, direct or substantive cotton dye- 

 stuffs, are probably the most important to the dyer, as 

 most of the colors are azo compounds, and dye vege- 

 table fibers direct from an aqueous bath, with the ad- 

 dition of some such salt as sodium chloride. Some of 

 them are also adapted to dyeing such animal fibers 

 as wool and silk, and the shades are usually very 

 fast. 



The second of these, the acid dyestuffs, are the so- 

 dium salts of sulphonic acids and the nitro-colors. 

 These are particularly useful in dyeing animal fibers. 



The third, or basic dyestuffs, are substantive to wool 

 and silk fibers, but may also be used to dye vegetable 

 fibers. They are not very fast colors, however, and are 

 not used very generally. 



The fourth, mordant dyes, are little used on account 

 of the difficulty of applying them. The one color for 

 which they are used extensively is Turkey-red on cotton 

 textures, the color being produced from alizarine and 

 an alumina lime and fatty-acid mordant. 



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