Cork-paper,  an  American  invention,  is  made
by  coating  one  side  of  a  thick,  soft  and  flexible
Cork  paper  with  a  preparation  of  glue,  gelatine,  and
molasses,  and  covering  it  with  finely  ground  cork
lightly  rolled  in.  This  paper  is  used  for  packing
bottles,  glassware,  etc.
Slate-paper,  which  takes  its  name  from  the
fact  that  it  can  be  cleansed  like  a  slate,  is  pre-
Slate  pared  from  the  regular  product,  of  the  required
thickness  and  consistency,  by  the  use  of  benzine,
followed  by  a  preparation  made  of  lead,  zinc
oxide,  turpentine,  seed-oil,  copal,  and  sandarach.
Soft  plate-paper  is  a  thick  unsized  paper,
especially  adapted  to  receive  impressions  for  fine
engravings  printed  from  steel  and  other  plates.
Filtering-paper,  much  used  by  chemists  and
druggists,  is  simply  unsized  open  or  porous
Filter  paper.  With  such  paper,  of  course,  the  process
of  manufacture  ceases  at  the  first  drying  or  crush-
ing rollers,  all  the  finishing  or  hardening  opera-
tions being  omitted.
Water-Marks  and  Varieties  of  Paper     1 1 1

Waterproof  papers  comprise  a  large  and  most
useful  class.  It  is  practically  only  within  the
past  twenty-five  years  that  a  process  has  been  Waterproof
known  and  employed  for  rendering  a  paper
waterproof  by  destroying  its  absorptive  proper-
ties. At  the  present  time  there  are  many  and
various  methods  used  in  waterproofing,  such  as
soaking  the  stock  in  dissolved  shellac  and  borax.
This  method  is  found  especially  satisfactory  in
waterproofing  heavy  paper  and  boards.  Another
process  is  by  brushing  the  surface  of  the  paper
with  boiled  oil,  and  paper  thus  prepared  was  for-
merly used  largely  in  lieu  of  bladders  and  gut-
skins  for  wrapping  butter,  covering  fruit-jars,  etc.,
but  it  has  been  almost  entirely  superseded  by  the
introduction  of  parchment-paper,  of  which  men-
tion will  be  made  later.
