The  advantages  of  this  kind  of  a  blackboard
are  its  comparative  cheapness,  its  opportunity


for  proper  coloring,  its  ready  adjustment  to  the
building,  and  the  readiness  with  which  the
material  may  be  obtained.  The  disadvantages
are,  the  absorption  of  moisture  from  within  or
without,  the  tendency  to  become  oily  from
contact  with  the  hands  of  the  children,  the
liability  to  crack  or  chip,  the  difficulty  of  get-
ting a  surface  which  will  take  the  chalk  readily,
evenly,  but  not  wastefully,  and  the  more  or  less
inevitable  alteration  in  the  color  of  the  board
through  washings  and  uneven  use.
(6)  Recent  years  have  seen  the  rapid  develop-
ment of  so-called  hyloplate  blackboards,  and
these,  when  thoroughly  made,  serve  their  pur-
pose for  a  time  satisfactorily.  In  general  this
style  of  blackboard  is  constructed  of  several
layers  of  heavy  specially  prepared  paper  so
fastened  and  pressed  together  as  to  make  a
solid  "  board  "  which  can  be  cut  to  suit  the
needs  and  requirements  of  any  schoolroom.
