﻿CLAYS 
  OF 
  IS^EW 
  YORK 
  Y95 
  

  

  One 
  mixture 
  of 
  tliis 
  type 
  is 
  as 
  follows 
  : 
  

  

  Composition 
  of 
  porcelain 
  mixture 
  for 
  the 
  production 
  of 
  bodies 
  of 
  low- 
  

   shrinkage 
  

  

  Parts 
  t 
  y 
  

   «tf 
  weight 
  

  

  Quartz 
  sand 
  120 
  

  

  Feldspar 
  (ISTorwegian) 
  85 
  

  

  Marble 
  3 
  

  

  Zettlitz 
  kaolin 
  60 
  to 
  70 
  

  

  Porcelain 
  sherds 
  ......! 
  20 
  to 
  60 
  

  

  It 
  has 
  also 
  been 
  found 
  that 
  porcelains 
  rich 
  in 
  fluxes 
  are 
  softy 
  

   while 
  those 
  poor 
  in 
  these 
  ingredients 
  are 
  hard 
  ; 
  neither 
  do 
  the 
  most 
  

   plastic 
  masses 
  always 
  show 
  the 
  greatest 
  shrinkage. 
  The 
  shrink- 
  

   age 
  of 
  Soger's 
  porcelain, 
  which 
  is 
  rich 
  in 
  fluxes, 
  occurs 
  mostly 
  in 
  

   drying,' 
  and 
  the 
  total 
  linear 
  shrinkage 
  is 
  10;^ 
  ; 
  it 
  expands 
  in 
  firing 
  

   when 
  a 
  certain 
  temperature 
  is 
  reached, 
  owing 
  to 
  the 
  high 
  percent- 
  

   age 
  (45;^) 
  of 
  quartz 
  which 
  it 
  contains. 
  Plastic 
  clays 
  give 
  a 
  very 
  

   smooth 
  surface 
  and 
  are 
  difficult 
  to 
  dry, 
  and 
  are 
  not 
  adapted 
  to 
  the; 
  

   manufacture 
  of 
  large 
  pieces. 
  A 
  mixture 
  poor 
  in 
  fluxes, 
  with 
  a 
  

   high 
  shrinkage, 
  can 
  be 
  very 
  lean 
  when 
  it 
  contains 
  no 
  sedimentary 
  

   clay 
  but 
  kaolin 
  as 
  the 
  plastic 
  element. 
  Bodies 
  of 
  good 
  plasticity, 
  

   but 
  low 
  in 
  fluxes, 
  are 
  of 
  comparatively 
  recent 
  introduction, 
  and 
  

   are 
  specially 
  adapted 
  to 
  large 
  objects 
  and 
  chemical 
  stoneware.-*- 
  

   Owing 
  to 
  its 
  high 
  percentage 
  of 
  clay 
  substance 
  and 
  low 
  fluxes,. 
  

   the 
  mass 
  acquires 
  little 
  translucency 
  when 
  burned 
  at 
  high 
  tem- 
  

   peratures, 
  but 
  stands 
  temperature 
  changes 
  very 
  well. 
  

  

  Hecht 
  has 
  recently 
  published 
  the 
  results 
  of 
  some 
  rather 
  detailed 
  

   investigations 
  on 
  the 
  composition 
  of 
  porcelains 
  and 
  white 
  earthen- 
  

   ware 
  bodies 
  poor 
  in 
  lime. 
  It 
  has 
  generally 
  been 
  considered 
  that 
  

   these 
  two 
  classes 
  of 
  ware 
  vary 
  in 
  composition 
  only 
  between 
  flxed 
  

   limits, 
  and 
  that 
  the 
  predominance 
  of 
  feldspar 
  in 
  the 
  mixture 
  was- 
  

   generally 
  confined 
  to 
  porcelain. 
  This, 
  however, 
  has 
  proved 
  to 
  be 
  

   an 
  error, 
  and 
  Hecht 
  finds 
  porcelains 
  which 
  are 
  low 
  in 
  feldspar,, 
  

   and 
  earthenware 
  bodies 
  rich 
  in 
  it. 
  The 
  following 
  examples 
  are 
  

   given.^ 
  

  

  ' 
  Chemiker 
  zeitung. 
  1894. 
  p. 
  821. 
  

  

  ^ 
  Thonindustrie 
  zeitung 
  . 
  1897. 
  no. 
  21, 
  p. 
  714. 
  

  

  