﻿792 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  not 
  be 
  less 
  than 
  125 
  pounds 
  a 
  square 
  incli, 
  though. 
  150 
  is 
  pref- 
  

   erable. 
  The 
  clay 
  should 
  not 
  shririk 
  excessively 
  in 
  burning, 
  and 
  

   should 
  give 
  a 
  vitrified 
  body 
  at 
  not 
  over 
  2100° 
  F. 
  if 
  possible, 
  for 
  the 
  

   lower 
  the 
  temperature 
  of 
  vitrification 
  the 
  greater 
  economy 
  in 
  fuel. 
  

   The 
  clay 
  should 
  however 
  be 
  sufficiently 
  refractory 
  to 
  hold 
  its 
  form 
  

   at 
  the 
  temperature 
  required 
  to 
  melt 
  the 
  glaze, 
  and 
  not 
  do 
  more 
  

   itself 
  than 
  vitrify 
  at 
  that 
  temperature. 
  The 
  fusible 
  impurities 
  in 
  a 
  

   stoneware 
  clay 
  should 
  be 
  sufficiently 
  high 
  to 
  cause 
  vitrification. 
  

   Ferric 
  oxid 
  forms 
  a 
  desirable 
  coloring 
  ingredient, 
  the 
  same 
  being 
  

   true 
  of 
  lime 
  if 
  not 
  in 
  excess 
  of 
  2^-3^. 
  iSulfur 
  in 
  any 
  combination 
  

   is 
  undesirable, 
  as 
  its 
  escape 
  at 
  high 
  temperatures 
  causes 
  blistering 
  

   of 
  the 
  ware. 
  

  

  In 
  mixing 
  two 
  clays, 
  the 
  one 
  is 
  generally 
  used 
  for 
  supplying 
  stiff- 
  

   ness 
  to 
  the 
  body 
  in 
  burning, 
  and 
  the 
  other, 
  fluxing 
  qualities. 
  

  

  For 
  common 
  earthenware, 
  almost 
  any 
  plastic 
  clay, 
  one 
  which 
  is 
  

   not 
  too 
  coarse, 
  suffices. 
  

  

  If 
  the 
  ware 
  is 
  to 
  be 
  glazed, 
  the 
  clay 
  should 
  be 
  sufficiently 
  re- 
  

   fractory, 
  so 
  that 
  at 
  the 
  temperature 
  required 
  to 
  melt 
  the 
  glaze, 
  it 
  

   will 
  not 
  bum 
  to 
  more 
  than 
  incipient 
  fusion. 
  

  

  Analyses 
  of 
  stoneware 
  clays 
  are 
  given 
  in 
  the 
  table 
  at 
  the 
  end 
  of 
  

   this 
  report. 
  In 
  addition, 
  are 
  given 
  here 
  the 
  average 
  of 
  10 
  stoneware 
  

   clays 
  now 
  in 
  use. 
  (E. 
  Orton 
  jr. 
  Clays 
  of 
  Ohio, 
  Ohio 
  geoL 
  sur. 
  

   V. 
  7, 
  pt 
  1, 
  p. 
  95) 
  

  

  Clay 
  base 
  56.65 
  

  

  Sand 
  37.45 
  

  

  Fluxes 
  4 
  . 
  44 
  

  

  Moisture 
  1 
  . 
  57 
  

  

  100.11 
  

   Total 
  silica 
  65 
  .09 
  

  

  