VEGETABLE TANNAGE 31 



protuberances known as " beard," which contains usually 

 about 40 per cent, of tannin. The cup alone contains 

 usually about 25 per cent, tannin, and the whole about 

 30 per cent. The valonia tannin has been thought to 

 contain two chemical individuals, only one of which produces 

 bloom. Parker and L,each 1 found that the tannin of the 

 cup produces more bloom than that of the beard, and that 

 Smyrna valonia yields more bloom than Greek. The more 

 bloom is deposited, the less acid will be produced. Under 

 all conditions the yield of bloom is large, and its deposition 

 in and on the leather assists materially in giving the weight 

 and water-resisting powers associated with sole leather 

 which has been largely tanned with valonia. The valonia 

 tannins have only a moderate affinity for hide, which, like 

 myrabolans, they penetrate very slowly. When used alone 

 the leather is less yellow than that from myrabolans, and 

 is also duller. After most of its bloom has been deposited 

 valonia makes a very suitable tannage for dressing leather, 

 and in conjunction with gambier has been largely thus 

 used. Since the outbreak of war the Turkish product has, 

 of course, not been available for importation. 



Sumach 2 is the other pyrogallol tan of commercial 

 importance. It consists of the leaves and small twigs of 

 the Sicilian sumach (Rhus coriaria) cultivated in Italy 

 extensively for export. The leaves are hand picked, dried 

 and often ground to powder. It contains 26-28 per cent, of 

 a tannin which yields little or no bloom, but much gallic acid. 

 It is an unstable tannin, and its infusion rapidly ferments. 

 Sumach is a very valuable tanning material, and when used 

 alone gives an exceedingly durable leather of excellent light 

 colour. It gives a soft mellow tannage, and is therefore 

 most suitable for light leather tanning, and is extensively 

 used for this purpose. It is used, nevertheless, in large 

 quantities by the heavy leather tanners for finishing pur- 

 poses, for it contains some organic reducing agent which 



1 /. S.S.I., 1903, 1184. 



8 Also spelt Sumac and Shumac, and always pronounced like the 

 latter. 



