254 BLACK DYES. OAK GALLS. 



nails, is a very permanent brown dye ; the colour not disappear- 

 ing, until the substance of the nails is changed by growth. It 

 is also employed for dyeing ordinary stuffs ; but it has not been 

 introduced into this country. 



399. The Vegetable kingdom affords several substances, 

 which are capable of themselves producing a permanent black 

 dye ; but a much larger amount of such materials is required, 

 than could thus be obtained ; and the black colour of our cloths 

 and stuffs is procured by a chemical process, of which one im- 

 portant ingredient is furnished by Plants. This process consists 

 in adding gallic acid to a solution of iron ; by which an insoluble 

 bluish black substance, the gallate of iron, is immediately formed. 

 If a cloth, therefore, previously steeped in a solution of iron, be 

 jmmersed in an infusion of any vegetable matter containing 

 gallic acid, a black dye will be communicated to it. Almost all 

 vegetable substances having an astringent taste, contain gallic 

 acid ; but especially the Oak tribe. It is from the abundance of 

 this acid in the Gall-nut (which is an excrescence resulting from 

 a kind of inflammation, excited by a wound of the soft tissue of 

 the leaves or young shoots by the gall-fly), that it takes its name. 

 Gall-nuts are not, however, formed upon the Oak of this country;* 

 but upon a smaller species, which grows wild in the countries 

 bordering on the Mediterranean. They are usually pounded and 

 then boiled in water, in which the eloth is steeped ; and this is 

 afterwards placed in the solution of iron (commonly termed cop- 

 peras). The colour thus communicated is not a deep black, but 

 rather a dark blue. It is improved by logwood, which is boiled 

 with the copperas ; and the stuff should have been previously 

 dyed of a deep blue, with indigo. A similar process is employed 

 in the manufacture of common black writing-ink, which essen- 

 tially consists of gallate of iron suspended in water by means of 

 a small quantity of gum ; and logwood is here also added to 

 improve the colour. Galls are imported from the East Indies, as 

 well as from Turkey ; but of late years they have been in less 



* The Oak Apples, however, are similar formations ; as are also various other 

 excrescences, formed upon different parts of the Oak, which is infested by several 

 species of Gall-fly 



