ALUM TANNAGES 175 



of salt, the hygroscopic nature of which would keep the 

 leather moist and thus interfere with a glossy finish. About 

 one-third the weight of the alum used is usually sufficient. 



All that has been said in Part III. as to the empty 

 nature of the chrome tannage is equally applicable to the 

 alum tannages. It is as necessary therefore to employ 

 filling agents. A fat liquor is quite satisfactory for many 

 purposes, but is too dark coloured and greasy for glove 

 leather. Egg yolk is the favourite emulsion in these cases. 

 It contains about 30 per cent, of an oil very similar to 

 olein and in very perfect emulsion. Olive oil is also largely 

 olein and is also used, being emulsified by the egg yolk and 

 effectively reducing the proportion required of this expensive 

 material. Flour is also used as a filling agent. It acts also 

 as a whitening agent and as an emulsifier. Its use enables 

 the tanner to obtain the required fullness without so much 

 greasiness. Thus softness and fullness may be obtained, 

 and yet a glossy finish be possible. It will be clear that 

 the more flour is used, the more oil may also be used. 



The materials mentioned, viz. alum, salt, flour, egg 

 yolk and olive oil, are all mixed together into a paste with 

 some amount of water. The goods are drummed in this 

 paste and then dried out. This operation is known as 

 " tawing." The goods are then '" aged " for several weeks 

 and finished as required. 



The manufacture of " glove kid " from lambskins and 

 kid skins is the most typical example of alum tannage. 

 Lambskins are unwoolled very usually by painting the 

 flesh with a mixture of lime and sodium sulphide. There 

 must not be too much of the latter on account of its tendency 

 to give harshness, a fatal defect in glove kid. The addition 

 of calcium chloride is desirable, and the skins, which should 

 be pulled as soon as possible, should be quickly placed in 

 soft water or weak lime. For kidskins a set of lime liquors 

 may be used, and in preference to sodium sulphide red 

 arsenic is employed. About one per cent, realgar on the 

 weight of the lime is used, but more often larger quantities 

 are preferred, even up to 6 per cent. The liming is thus 



