﻿640 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  sociated 
  with 
  it, 
  the 
  composition 
  of 
  the 
  fire 
  gases, 
  the 
  degree 
  of 
  

   sintering 
  and 
  the 
  temperature 
  of 
  the 
  kiln. 
  

  

  The 
  red 
  coloration 
  nsuallj 
  caused 
  by 
  iron 
  is 
  well 
  known, 
  and 
  the 
  

   other 
  effects 
  of 
  iron 
  are 
  mentioned 
  on 
  page 
  517. 
  An 
  excess 
  of 
  

   lime, 
  magnesia 
  or 
  alumina 
  tends 
  to 
  exert 
  a 
  bleaching 
  action 
  on 
  the 
  

   iron, 
  and 
  produce 
  a 
  buff 
  tint. 
  . 
  

  

  It 
  is 
  asserted 
  bv 
  Soger 
  {Ges. 
  Schrift. 
  p. 
  282) 
  that 
  it 
  requires- 
  

   5^ 
  of 
  ferric 
  oxid 
  to 
  give 
  a 
  pronounced 
  red 
  color, 
  which 
  increases- 
  

   with 
  the 
  amount 
  of 
  iron, 
  up 
  to 
  about 
  20 
  fc. 
  

  

  Knowing 
  the 
  effect 
  of 
  the 
  different 
  ingredients 
  on 
  the 
  color 
  of 
  

   the 
  burned 
  clay, 
  it 
  is 
  possible 
  when 
  certain 
  results 
  are 
  desired 
  ta 
  

   add 
  the 
  ingredients 
  to 
  the 
  clay 
  in 
  case 
  they 
  are 
  lacking. 
  Thus 
  a 
  red 
  

   burning 
  clay 
  might 
  be 
  changed 
  to 
  a 
  buff 
  burning 
  one 
  by 
  adding 
  

   to 
  it 
  a 
  white 
  or 
  whitish 
  burning 
  clay 
  containing 
  a 
  high 
  amount 
  of 
  

   alumina, 
  and, 
  depending 
  on 
  the 
  amount 
  added, 
  we 
  should 
  get 
  shades- 
  

   passing 
  from 
  red 
  through 
  brown, 
  yellowish 
  brown, 
  to 
  yellow. 
  Marl 
  

   produces 
  a 
  similar 
  result. 
  

  

  The 
  fire 
  gases 
  may 
  be 
  either 
  reducing 
  or 
  oxidizing, 
  and 
  during 
  

   the 
  burning 
  of 
  a 
  kiln 
  these 
  conditions 
  are 
  apt 
  to 
  alternate 
  at 
  times,, 
  

   but 
  while 
  cooling 
  down 
  the 
  action 
  of 
  the 
  fire 
  is 
  with 
  few 
  excep- 
  

   tions 
  oxidizing. 
  

  

  One 
  effect 
  of 
  the 
  sintering 
  is 
  to 
  cause 
  the 
  clay 
  to 
  shrink 
  more- 
  

   and 
  become 
  denser, 
  and 
  this 
  of 
  itself 
  is 
  sufficient 
  to 
  deepen 
  the 
  

   color. 
  

  

  The 
  color 
  to 
  which 
  a 
  clay 
  naturally 
  burns 
  as 
  a 
  result 
  of 
  its 
  con- 
  

   stituents, 
  is 
  best 
  shown 
  on 
  the 
  fractured 
  surface 
  of 
  a 
  brick, 
  as 
  the- 
  

   fire 
  gases 
  have 
  not 
  been 
  able 
  to 
  exert 
  any 
  effect 
  on 
  the 
  interior 
  of 
  

   the 
  product. 
  

  

  The 
  surface 
  coloration 
  of 
  a 
  burned 
  brick 
  may 
  often 
  be 
  the 
  same 
  

   as 
  that 
  of 
  the 
  interior 
  portion, 
  but 
  at 
  other 
  times 
  it 
  may 
  differ 
  from 
  

   it. 
  This 
  is 
  due 
  to 
  the 
  accumulation 
  of 
  soluble 
  salts, 
  which 
  have 
  

   been 
  drawn 
  from 
  the 
  interior 
  of 
  the 
  brick 
  to 
  the 
  surface, 
  either 
  in 
  

   burning, 
  water-smoking 
  or 
  drying. 
  

  

  Another 
  cause 
  of 
  difference 
  in 
  color 
  between 
  the 
  surface 
  and 
  in- 
  

  

  