﻿794 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Porcelain 
  

  

  The 
  same 
  materials 
  are 
  used 
  as 
  in'tlie 
  manufacture 
  of 
  white 
  

   granite, 
  but 
  the 
  proportions 
  are 
  usually 
  different; 
  the 
  ware 
  is 
  

   burned 
  to 
  vitrification, 
  so 
  that 
  the 
  body 
  is 
  transparent, 
  and 
  the 
  

   fracture 
  of 
  it 
  would 
  show 
  a 
  vitreous 
  luster. 
  

  

  Porcelain 
  which 
  is 
  fluxed 
  by 
  feldspar 
  is 
  spoken 
  of 
  as 
  spar 
  china. 
  

   It 
  shows 
  a 
  slightly 
  yellowish 
  color 
  by 
  transmitted 
  light, 
  while 
  

   porcelain 
  fluxed 
  by 
  calcined 
  bones 
  in 
  part 
  replacing 
  the 
  feldspar 
  is 
  

   spoken 
  of 
  as 
  bone 
  china. 
  It 
  shows 
  a 
  bluish 
  white 
  color 
  by 
  trans- 
  

   mitted 
  light. 
  

  

  The 
  proportion 
  of 
  fluxes 
  is 
  greater 
  in 
  porcelain 
  than 
  in 
  white 
  

   earthenware 
  ; 
  but 
  still, 
  taking 
  porcelains 
  as 
  a 
  whole, 
  there 
  is 
  a 
  wide 
  

   range 
  in 
  their 
  composition, 
  as 
  will 
  be 
  seen 
  from 
  the 
  following 
  

   figures 
  representing 
  the 
  range 
  of 
  the 
  ingredients 
  used 
  in 
  the 
  manu- 
  

   facture 
  of 
  hard 
  porcelains. 
  (Hecht.- 
  Dammer, 
  Chem. 
  Tech. 
  

   1 
  :773 
  and 
  following 
  .) 
  

  

  Per 
  cent 
  

  

  Olay 
  substance 
  40-66 
  

  

  Quartz 
  12-40 
  

  

  Feldspar 
  15-30 
  

  

  Carbonate 
  of 
  lime 
  (at 
  times) 
  , 
  . 
  6 
  

  

  The 
  variation 
  outside 
  of 
  these 
  limits 
  should 
  be 
  ver^^ 
  small, 
  for 
  if 
  

   the 
  clay 
  substance 
  gets 
  below 
  40^, 
  the 
  refractoriness 
  decreases 
  con- 
  

   siderably, 
  as 
  does 
  also' 
  the 
  ability 
  of 
  the 
  ware 
  to 
  withstand 
  sudden 
  

   changes 
  of 
  temperature. 
  

  

  As 
  excessive 
  shrinkage 
  in 
  burning 
  tends 
  to 
  cause 
  cracking 
  and 
  

   warping, 
  one 
  aim 
  of 
  ceramic 
  chemists 
  has 
  been 
  to 
  produce 
  bodies 
  of 
  

   low 
  shrinkage; 
  and 
  experiments 
  have 
  indicated 
  that 
  the 
  use 
  of 
  

   porcelain 
  sherds 
  ground 
  up 
  gives 
  a 
  much 
  more 
  homogeneous 
  mass 
  

   than 
  can 
  be 
  obtained 
  by 
  the 
  use 
  of 
  quartz. 
  {Chemihei^ 
  zeitung. 
  

   1895. 
  p. 
  89) 
  

  

  