﻿566 
  

  

  NEW 
  YORX 
  STATE 
  MUSEUM 
  

  

  color 
  of 
  clay 
  and 
  specially 
  influence 
  the 
  coloring 
  action 
  of 
  iron. 
  

   Calcareous 
  clays 
  in 
  burning 
  develop 
  a 
  yellow, 
  instead 
  of 
  a 
  red 
  color, 
  

   and 
  at 
  the 
  temperature 
  of 
  vitrification 
  this 
  passes 
  into 
  a 
  yellowisli 
  

   green. 
  Seger 
  has 
  shown 
  that 
  the 
  color 
  of 
  a 
  hard 
  burned 
  clay 
  de- 
  

   pends 
  on 
  the 
  relation 
  of 
  iron 
  oxid 
  to 
  alumina, 
  and 
  in 
  calcareous 
  

   clays 
  on 
  the 
  ratio 
  of 
  iron 
  oxid 
  tO' 
  lime. 
  

  

  Diimmler 
  in 
  his 
  table 
  of 
  analyses-^ 
  shows 
  the 
  ratio 
  of 
  iron 
  and 
  

   manganese 
  oxid 
  to 
  the 
  sum 
  of 
  nonvolatile 
  constituents, 
  and 
  the 
  

   ratio 
  of 
  lime 
  and 
  magnesia 
  oxid 
  to 
  iron 
  and 
  manganese 
  oxids. 
  From 
  

   this 
  it 
  follows 
  that 
  in 
  all 
  clays 
  in 
  which 
  the 
  combined 
  iron 
  and 
  

   manganese 
  oxids 
  are 
  more 
  than 
  -^^^ 
  of 
  the 
  amount 
  of 
  the 
  total 
  non- 
  

   volatiles, 
  a 
  distinct 
  red 
  color 
  is 
  produced, 
  if 
  at 
  the 
  same 
  time 
  the 
  

   sum 
  of 
  the 
  two 
  is 
  more 
  than. 
  twO' 
  and 
  a 
  half 
  times 
  greater 
  than 
  the 
  

   combined 
  magnesia 
  oxids. 
  

  

  Of 
  course 
  the 
  grade 
  of 
  firing 
  has 
  an 
  influence 
  on 
  the 
  color, 
  and 
  

   in 
  addition 
  the 
  composition 
  of 
  the 
  kiln 
  gases 
  might 
  exert 
  a 
  marked 
  

   influence. 
  Thus, 
  for 
  instance, 
  clays 
  high 
  in 
  iron 
  burned 
  slate 
  blue 
  

   in 
  a 
  reducing 
  fire, 
  while 
  yellow 
  burning 
  noncalcareous 
  clay 
  takes 
  

   on 
  a 
  distinct 
  red 
  color, 
  if 
  subjected 
  to 
  alternating 
  reducing 
  and 
  

   oxidizing 
  action. 
  (Diimmler. 
  Die 
  ziegel 
  fahrikation, 
  p. 
  42) 
  

  

  The 
  shades 
  which 
  ferric 
  oxid 
  takes 
  in 
  burning 
  vary 
  partly 
  with 
  

   the 
  nature 
  of 
  its 
  formation. 
  According 
  to 
  Seger 
  that 
  which 
  is 
  made 
  

   from 
  ferric 
  nitrate 
  bums 
  brown 
  red, 
  that, 
  from 
  iron 
  sulfate 
  by 
  

   ignition 
  is 
  reddish 
  orange. 
  

  

  Heating 
  deepens 
  the 
  color 
  of 
  the 
  ferric 
  oxid 
  with 
  increase 
  of 
  the 
  

   temperature; 
  and 
  this 
  holds 
  true 
  for 
  all 
  ferruginous 
  clays, 
  so 
  that 
  

   in 
  general 
  the 
  color 
  of 
  clay 
  products 
  containing 
  iron 
  will 
  be 
  darker 
  

   the 
  higher 
  the 
  temperature 
  to 
  which 
  they 
  are 
  burned. 
  

  

  A 
  small 
  percentage 
  of 
  iron 
  in 
  a 
  clay 
  produces 
  a 
  buif 
  color 
  when 
  

   burned 
  to, 
  say 
  2000° 
  F., 
  but 
  might 
  give 
  a 
  red 
  if 
  burned 
  to 
  2500° 
  F. 
  

  

  If 
  a 
  clay 
  contains 
  enough 
  iron 
  to 
  color 
  it 
  red 
  when 
  burned 
  to 
  

   incipient 
  fusion, 
  it 
  may 
  become 
  deep 
  red 
  or 
  brownish 
  at 
  the 
  tem- 
  

   perature 
  of 
  vitrification, 
  and 
  black 
  at 
  the 
  temperature 
  of 
  viscosity. 
  

  

  1 
  Die 
  ziegel 
  fabrikation. 
  

  

  