﻿CLAYS 
  OF 
  NEW 
  YORK 
  653 
  

  

  ing 
  quartz 
  and 
  feldspar 
  to 
  clay 
  is 
  rather 
  expensive, 
  and 
  these 
  two 
  

   could 
  probably 
  be 
  replaced 
  by 
  the 
  use 
  of 
  a 
  feldspathic 
  quartz 
  sand. 
  

  

  Experiments 
  of 
  this 
  nature 
  carried 
  out 
  by 
  Hecht 
  (Thonindus- 
  

   trie 
  zeitung. 
  1894. 
  p. 
  309) 
  indicated 
  that 
  it 
  is 
  undesirable 
  in 
  most 
  

   cases 
  to 
  decrease 
  the 
  clay 
  substance 
  below 
  30^, 
  and 
  that 
  if 
  the 
  clay 
  

   contain 
  over 
  50^ 
  most 
  of 
  the 
  glazes 
  adhere 
  with 
  difficulty. 
  

  

  He 
  found 
  that 
  colored 
  glazes 
  with 
  a 
  formula 
  

  

  l."?SSl-'^^lA4SiO, 
  

   held 
  on 
  mixtures 
  whose 
  rational 
  composition 
  was: 
  

  

  Clay 
  sub- 
  

   stance 
  . 
  ... 
  50 
  50 
  50 
  50 
  40 
  30 
  30 
  30 
  30 
  30 
  30 
  

  

  Quartz 
  .... 
  40 
  30 
  20 
  10 
  50 
  60 
  50 
  40 
  30 
  20 
  10 
  

  

  Feldspar... 
  5 
  15 
  25 
  35 
  5 
  5 
  15 
  25 
  35 
  45 
  55 
  

  

  Lime 
  car- 
  

   bonate 
  ... 
  65555555555 
  

  

  Hecht 
  in 
  his 
  experiments 
  used 
  iron, 
  and 
  pink 
  glazes, 
  because 
  

   they 
  represented 
  extremes 
  of 
  composition. 
  He 
  found 
  that 
  the 
  glazes 
  

   held 
  best 
  when 
  the 
  clay 
  substance 
  was 
  30;^^. 
  As 
  the 
  clay 
  substance 
  

   increased, 
  the 
  adhesion 
  of 
  teo 
  clay 
  decreased, 
  and 
  it 
  did 
  the 
  same 
  

   with 
  an 
  increase 
  of 
  the 
  feldspar, 
  while 
  it 
  adhered 
  better 
  as 
  the 
  

   quartz 
  increased 
  in 
  amount. 
  

  

  The 
  tendency 
  of 
  the 
  glaze 
  to 
  craze 
  also 
  becomes 
  greater 
  with 
  

   the 
  size 
  of 
  the 
  quartz 
  grain, 
  the 
  reason 
  being 
  that 
  the 
  greater 
  the 
  

   grain 
  the 
  more 
  difficult 
  it 
  is 
  for 
  a 
  thorough 
  chemical 
  action 
  to 
  take 
  

   place 
  between 
  the 
  particles 
  of 
  the 
  clay 
  and 
  those 
  of 
  the 
  brick. 
  

  

  Methods 
  of 
  manufacturing 
  brick 
  

   Bricka 
  are 
  usually 
  made 
  by 
  one 
  of 
  the 
  follo^ving 
  four 
  processes. 
  

  

  Soft 
  mud 
  

  

  Stiff 
  mud 
  or 
  wire-cut 
  

   Dry 
  press 
  

   Semi-dry 
  press 
  ' 
  

  

  