﻿CLAYS 
  OF 
  K^EW 
  YORK: 
  779 
  

  

  for 
  this 
  purpose, 
  only 
  liard 
  fire 
  or 
  undergiazed 
  colors 
  can 
  be 
  used 
  

   (Dllmmler 
  Ziegel 
  Fahrikation. 
  p. 
  95). 
  In 
  producing 
  definite 
  and 
  

   distinct 
  colors 
  the 
  composition 
  of 
  the 
  glaze 
  exerts 
  as 
  much 
  effect 
  as 
  

   the 
  character 
  of 
  the 
  coloring 
  material. 
  It 
  is 
  therefore 
  highly 
  

   essential 
  that 
  the 
  colors 
  used 
  shall 
  always 
  be 
  of 
  the 
  same 
  compo- 
  

   sition, 
  be 
  ground 
  to 
  the 
  same 
  degree 
  of 
  fineness, 
  and 
  burned 
  at 
  the 
  

   same 
  temperature. 
  If 
  new 
  glazes 
  or 
  colors 
  are 
  used, 
  they 
  should 
  

   first 
  be 
  tried 
  experimentally. 
  In 
  the 
  process 
  of 
  burning, 
  the 
  glaze 
  

   may 
  or 
  may 
  not 
  exert 
  action 
  on 
  the 
  imderlying 
  coloring 
  material. 
  

   In 
  8ome 
  cases 
  the 
  color 
  will 
  dissolve 
  in 
  the 
  glaze, 
  in 
  others 
  it 
  will 
  

   only 
  become 
  suspended 
  in 
  it, 
  but 
  in 
  the 
  latter 
  cases 
  the 
  shades 
  are 
  

   not 
  often 
  soft, 
  and 
  the 
  change 
  from 
  one 
  color 
  to 
  another 
  will 
  be 
  

   sudden. 
  If 
  on 
  the 
  other 
  hand 
  a 
  color 
  is 
  easily 
  soluble 
  in 
  the 
  glaze, 
  

   there 
  is 
  the 
  danger 
  that 
  it 
  may 
  run, 
  causing 
  the 
  desig'n 
  to 
  be 
  

   blurred. 
  In 
  order 
  to 
  prevent 
  this, 
  the 
  coloring 
  materials 
  are 
  gen- 
  

   erally 
  combined 
  with 
  others, 
  so 
  that 
  compounds 
  of 
  the 
  spinel 
  type 
  

   are 
  obtained. 
  

  

  To 
  prevent 
  hard 
  colors 
  several 
  devices 
  are 
  employed, 
  such 
  as 
  

   substituting 
  for 
  a 
  portion 
  of 
  the 
  coloring 
  material 
  a 
  slight 
  amount 
  

   of 
  arsenic, 
  or 
  placing 
  a 
  little 
  arsenic 
  in 
  the 
  kiln. 
  This 
  method 
  is 
  

   most 
  advantageously 
  employed 
  when 
  cobalt 
  colors 
  are 
  used. 
  

  

  In 
  addition 
  to 
  undergiazed 
  painting, 
  slip 
  or 
  engobe 
  decoration 
  is 
  

   used. 
  This 
  consists 
  in 
  applying 
  white 
  or 
  colored 
  clay 
  paste 
  to 
  the 
  

   white 
  or 
  colored 
  tile. 
  

  

  The 
  body 
  can 
  also 
  be 
  colored 
  by 
  dipping 
  it 
  into 
  hydrochloric 
  or 
  

   acetic 
  acid 
  solution 
  of 
  the 
  coloring 
  metallic 
  oxids. 
  In 
  this 
  case 
  the 
  

   product 
  is 
  to 
  be 
  once 
  more 
  subjected 
  to 
  a 
  slight 
  ignition. 
  

  

  In 
  slip 
  painting 
  the 
  slip 
  is 
  made 
  of 
  a 
  mixture 
  of 
  the 
  powdered 
  

   tile 
  glaze 
  and 
  metallic 
  oxid 
  or 
  underglaze 
  colors. 
  These 
  decorated 
  

   pieces 
  are 
  dried 
  and 
  burned 
  at 
  the 
  temperature 
  of 
  the 
  melting 
  of 
  the 
  

   glaze. 
  The 
  whole 
  is 
  then 
  covered 
  with 
  a 
  thin 
  coating 
  of 
  glaze 
  and 
  

   burned 
  once 
  more. 
  If 
  the 
  slip 
  contains 
  50^ 
  or 
  more 
  of 
  glazing 
  ma- 
  

   terial, 
  the 
  second 
  glazing 
  operation 
  is 
  not 
  necessary. 
  

   . 
  Overglaze 
  decoration 
  requires 
  strongly 
  coloring 
  oxids 
  which 
  are 
  

   mixed 
  with 
  some 
  easily 
  fused 
  material, 
  and 
  rubbed 
  together 
  with 
  

  

  