﻿810 
  ]\'EW 
  YORK 
  STATE 
  MUSEUM 
  

  

  state 
  or 
  after 
  burning. 
  In 
  the 
  burning 
  the 
  ingi'edients 
  of 
  this 
  

   mixture 
  unite 
  during 
  fusion 
  and 
  cover 
  the 
  surface 
  with 
  an 
  im- 
  

   pervious 
  glassy 
  coat. 
  

  

  Pottery 
  glazes 
  are 
  generally 
  of 
  two 
  kinds, 
  raw 
  or 
  fritted. 
  The 
  

   former 
  consists 
  usually 
  of 
  some 
  mixture 
  of 
  metallic 
  oxids, 
  which 
  

   is 
  sprayed 
  on 
  the 
  surface 
  of 
  the 
  raw 
  clay. 
  In 
  the 
  case 
  of 
  the 
  

   latter, 
  the 
  ingredients 
  of 
  the 
  glaze 
  are 
  first 
  fused 
  together, 
  forming 
  

   what 
  is 
  knovTn 
  as 
  a 
  frit, 
  the 
  frit 
  is 
  then 
  ground 
  very 
  fine, 
  and 
  

   mixed 
  with 
  water, 
  this 
  mixture 
  being 
  applied 
  to 
  the 
  surface 
  of 
  the 
  

   green 
  ware. 
  It 
  is 
  specially 
  necessary 
  to 
  prepare 
  such 
  a 
  frit 
  when 
  

   the 
  glaze 
  contains 
  any 
  soluble 
  salts, 
  the 
  object 
  of 
  the 
  fritting 
  being 
  

   to 
  render 
  these 
  salts 
  insoluble. 
  The 
  fritting 
  is 
  usually 
  done 
  in 
  a 
  

   special 
  furnace, 
  which 
  has 
  the 
  bottom 
  sloping 
  toward 
  one 
  point, 
  so 
  

   that 
  the 
  melted 
  material 
  can 
  be 
  run 
  out 
  into 
  a 
  tank 
  of 
  water, 
  at 
  the 
  

   proper 
  time. 
  Certain 
  frits, 
  either 
  on 
  account 
  of 
  the 
  difficulty 
  

   with 
  which 
  they 
  flow 
  on 
  melting 
  or 
  owing 
  to 
  the 
  corrosive 
  action 
  

   they 
  exert 
  when 
  fused, 
  can 
  not 
  be 
  melted 
  in 
  the 
  furnace, 
  but 
  are 
  

   fused 
  in 
  a 
  special 
  crucible 
  or 
  sagger. 
  

  

  The 
  proper 
  preparation 
  of 
  the 
  glaze 
  often 
  requires 
  much 
  skill 
  

   and 
  experience 
  ; 
  for 
  the 
  production 
  of 
  a 
  uniform 
  coating 
  of 
  glaze 
  

   on 
  the 
  surface 
  of 
  the 
  ware 
  is 
  influenced 
  by 
  many 
  different 
  things, 
  

   such 
  as 
  the 
  degree 
  of 
  porosity 
  of 
  the 
  ware 
  when 
  glazed, 
  the 
  cleanli- 
  

   ness 
  of 
  the 
  surface 
  to 
  be 
  coated, 
  the 
  consistency 
  of 
  tlie 
  glaze, 
  etc. 
  

  

  If 
  the 
  density 
  of 
  the 
  body 
  is 
  too 
  great, 
  or 
  there 
  happens 
  to 
  be 
  a 
  

   film 
  of 
  dust 
  or 
  fat 
  on 
  the 
  surface, 
  the 
  glaze 
  is 
  apt 
  to 
  contract 
  into 
  

   drops 
  during 
  the 
  burning. 
  If 
  the 
  glaze 
  is 
  too 
  refractory, 
  or 
  the 
  

   kiln 
  fire 
  is 
  not 
  hot 
  enough, 
  the 
  glaze 
  will 
  not 
  be 
  homogeneous, 
  but 
  

   show 
  little 
  dots 
  and 
  pin 
  holes. 
  A 
  frequent 
  fault 
  is 
  the 
  tearing 
  or 
  

   springing 
  off 
  of 
  glaze, 
  which 
  is 
  due 
  to 
  the 
  glaze 
  and 
  the 
  body 
  

   having 
  a 
  different 
  coefficient 
  of 
  expansion. 
  If 
  that 
  of 
  the 
  glaze 
  

   is 
  greater, 
  the 
  body 
  is 
  apt 
  to 
  tear, 
  whereas, 
  if 
  the 
  reverse 
  is 
  true, 
  

   the 
  glaze 
  spalls 
  off. 
  It 
  may 
  be 
  said 
  in 
  general 
  that 
  with 
  an 
  

   increase 
  in 
  the 
  amount 
  of 
  fluxes 
  the 
  coefficient 
  of 
  expansion 
  of 
  a 
  

   glaze 
  increases, 
  while 
  it 
  decreases 
  with 
  the 
  amount 
  of 
  acids. 
  The 
  

  

  