408  PREPARATION  OF  FANCY  LEATHERS,  ETC. 
a  decoction  of  alum  ;  and,  lastly,  as  already  stated,  the  birch- 
tree  oil  is  used  in  currying  it. 
Enamel  Leather. — This  class  of  leather  is  usually  prepared 
with  calf  and  sheep  skins  tanned  in  the  ordinary  manner.  They 
are  dyed  black  by  rubbing  them  over  with  a  decoction  of  log- 
wood, and  then  iron  liquor  or  acetate  of  iron.  The  leather  is 
softened  with  a  little  oil,  and  is  ready  to  receive  a  varnish, 
which  is  applied  by  means  of  a  brush,  and  composed  of  bitu- 
men of  Judea,  copal  varnish,  oil  varnish,  turpentine,  and  boiled 
oil. 
Taived  or  Kid  Leathers. — The  manufacture  of  this  class  of 
leathers  differs  entirely  from  those  already  described,  as  their 
preservative  qualities  are  imparted  by  quite  different  substances 
from  those  used  with  other  leathers,  the  preservative  action  of 
the  tannin  being  substituted  by  that  of  a  mixture  of  alum  and 
common  salt.  Let  us  examine  together  a  few  points  connected 
with  the  production  of  this  class  of  leather.  One  of  the  most 
interesting  characteristics  is  the  method  of  unhairing  sheep, 
lamb,  and  kid  skins,  after  they  have  been  well  washed  and 
fleshed  on  the  beam.  The  old  process  of  unhairing  by  smearing 
on  the  fleshy  side  with  a  milk  of  lime,  was  improved  by  mixing 
with  the  lime  a  certain  amount  of  orpiment,  or  sulphuret  of 
arsenic,  but  Mr.  Robert  Warrington  having  ascertained  that 
the  rapid  removal  of  hair  in  this  case  was  not  due  to  the  ar- 
senic, but  to  the  formation  of  sulphuret  of  calcium,  proposed, 
with  great  foresight,  the  following  mixture  as  a  substitute  for 
the  dangerous  and  poisonous  substance  called  orpiment — viz., 
three  parts  of  polysulphuret  of  sodium,  ten  parts  of  slacked 
lime,  and  ten  parts  of  starch.  The  polysulphuret  of  sodium 
may  be  advantageously  replaced  by  the  polysulphuret  of  cal- 
cium. The  skins,  unhaired  by  any  of  these  processes,  are  now 
ready  to  be  placed  in  a  bran  or  rye  bath,  as  with  Morocco 
leather,  or  in  a  weak  solution  of  vitriol,  to  remove,  as  already 
stated,  the  lime.  After  the  lime  has  been  thoroughly  removed 
from  the  skins,  they  are  dipped  in  what  is  called  the  white  bath, 
which  is  composed,  for  100  skins,  of  13  to  20  lbs.  of  alum,  and 
4  to  5  lbs.  of  chloride  of  sodium  or  common  salt,  and  the  skins 
are  either  worked  slowly  in  fchis  bath  or  introduced  into  a  re- 
volving cylinder  to  facilitate  the  penetration  of  the  preservative 
