﻿CLAYS 
  OF 
  NEW 
  YORK 
  797 
  

  

  that 
  a 
  great 
  number 
  hold, 
  without 
  crazing, 
  on 
  bodies 
  having 
  the 
  

   following 
  composition, 
  whether 
  burned 
  in 
  a 
  hard 
  porcelain 
  fire 
  

   or 
  moderate 
  white 
  earthenware 
  fire: 
  

  

  Composition 
  of 
  bodies 
  on 
  which 
  many 
  earthenware 
  and 
  porcelain 
  g-lazes 
  

  

  do 
  not 
  craze 
  

  

  Per 
  cent 
  

  

  80 
  ... 
  . 
  Claj 
  substance 
  " 
  30 
  

  

  20 
  ... 
  . 
  Quartz 
  and 
  feldspar 
  70 
  

  

  The 
  degree 
  of 
  tenacity 
  with 
  which 
  the 
  glazes 
  hold 
  depends 
  on 
  

   the 
  temperature 
  at 
  which 
  the 
  biscuit 
  and 
  glazed 
  ware 
  are 
  burned, 
  

   and 
  to 
  a 
  greater 
  or 
  less 
  extent 
  on 
  the 
  relative 
  amounts 
  of 
  kaolin 
  

   and 
  plastic 
  stoneware 
  clay 
  in 
  the 
  body. 
  

  

  The 
  practical 
  value 
  of 
  the 
  above 
  observations 
  is 
  that 
  it 
  points 
  

   toward 
  much 
  greater 
  possibilities 
  in 
  undergiaze 
  decoration, 
  for 
  

   while 
  in 
  the 
  past 
  such 
  work 
  could 
  only 
  be 
  done 
  under 
  hard 
  fire 
  

   glazes, 
  we 
  can 
  now 
  paint 
  the 
  porcelain 
  with 
  undergiaze 
  colors 
  

   hitherto 
  used 
  only 
  for 
  white 
  earthenware 
  and 
  cover 
  them 
  with 
  

   easily 
  fusible 
  muffle 
  glazes. 
  

  

  The 
  effect 
  of 
  excessive 
  grinding 
  on 
  the 
  ingredients 
  of 
  a 
  porcelain 
  

   mixture 
  has 
  recently 
  been 
  shown 
  to 
  be 
  serious. 
  (Sprechsaal. 
  

   1896. 
  no. 
  29. 
  p. 
  812) 
  It 
  was 
  found 
  that, 
  when 
  a 
  mixture 
  of 
  

   kaolin, 
  quartz 
  and 
  feldspar 
  was 
  ground 
  in 
  a 
  ball 
  mill 
  for 
  120 
  

   hours, 
  the 
  ware 
  in 
  burning 
  became 
  blistered 
  and 
  showed 
  a 
  fijiely 
  

   vesicular 
  structure 
  throughout. 
  If 
  on 
  the 
  other 
  hand 
  only 
  the 
  

   quartz 
  and 
  feldspar 
  were 
  ground 
  for 
  96 
  hours, 
  and 
  the 
  kaolin 
  

   then 
  added, 
  the 
  result 
  was 
  a 
  strong, 
  translucent 
  porcelain 
  of 
  normal 
  

   color, 
  free 
  from 
  blisters. 
  The 
  experiments 
  suggest 
  how 
  porce- 
  

   lains 
  which 
  are 
  only 
  slightly 
  transparent 
  can 
  be 
  made 
  more 
  so. 
  

  

  Delft 
  ware. 
  This 
  name 
  was 
  originally 
  applied 
  to 
  a 
  white 
  ware 
  

   made 
  at 
  Delft 
  in 
  Holland, 
  which 
  was 
  ornamented 
  with 
  blue 
  de- 
  

   signs 
  representing 
  Dutch 
  scenery. 
  It 
  is 
  extensively 
  manufactured 
  

   at 
  many 
  localities 
  at 
  the 
  present 
  day, 
  the 
  body 
  of 
  the 
  ware 
  being 
  

   porcelain 
  or 
  white 
  earthenware. 
  The 
  articles 
  which 
  are 
  usually 
  

   decorated 
  under 
  the 
  glaze 
  include 
  clocks, 
  vases, 
  jardinieres, 
  toilet 
  

   articles, 
  etc. 
  

  

  