﻿652 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  The 
  matter 
  of 
  glazing 
  and 
  enameling 
  is 
  the 
  most 
  difficult 
  part 
  of 
  

   the 
  whole 
  process 
  of 
  manufacture, 
  and 
  as 
  such 
  is 
  kept 
  secret, 
  by 
  the 
  

   maker 
  ks 
  far 
  as 
  the 
  details 
  are 
  concerned. 
  In 
  general 
  it 
  may 
  be 
  

   said, 
  however, 
  that 
  the 
  enamel 
  is 
  simply 
  a 
  mixture 
  of 
  clays 
  similar 
  

   to 
  that 
  used 
  in 
  making 
  good 
  porcelain, 
  which 
  is 
  applied 
  to 
  the 
  sur- 
  

   face 
  of 
  the 
  brick 
  in 
  the 
  condition 
  of 
  a 
  thick 
  liquid 
  or 
  slip. 
  This 
  

   enamel, 
  when 
  dry, 
  is 
  coated 
  with 
  a 
  fusible 
  glaze, 
  such 
  as 
  is 
  used 
  

   for 
  ordinary 
  porcelain. 
  

  

  Enamel 
  brick 
  are 
  usually 
  burned 
  in 
  saggers, 
  placed 
  in 
  a 
  down- 
  

   draft 
  kiln, 
  or 
  sometimes 
  even 
  in 
  a 
  muffle 
  kiln. 
  The 
  double 
  fire 
  

   method 
  mentioned 
  above 
  greatly 
  increases 
  the 
  cost 
  of 
  manufacture. 
  

  

  Glazed 
  brick. 
  By 
  thia 
  we 
  understand 
  a 
  brick 
  which 
  is 
  covered 
  

   by 
  a 
  transparent 
  glaze, 
  and 
  not 
  an 
  opaque 
  enamel. 
  

  

  The 
  best 
  results 
  are 
  probably 
  obtained 
  by 
  glazing 
  vitrified 
  bricks, 
  

   as 
  porous 
  ones 
  are 
  seldom 
  able 
  to 
  resist 
  the 
  weather, 
  specially 
  in 
  

   severe 
  climates. 
  

  

  If 
  the 
  glaze 
  is 
  applied 
  to 
  green 
  brick, 
  which 
  is 
  by 
  far 
  the 
  cheapest 
  

   method 
  and 
  the 
  two 
  burned 
  together, 
  the 
  glaze 
  mil 
  often 
  show 
  

   crazing 
  under 
  certain 
  conditions, 
  and 
  it 
  is 
  found 
  that 
  there 
  should 
  

   be 
  a 
  certain 
  amount 
  of 
  agreement 
  between 
  the 
  composition 
  of 
  the 
  

   clays 
  and 
  that 
  of 
  the 
  brick, 
  so 
  that 
  they 
  will 
  not 
  only 
  have 
  a 
  simi- 
  

   lar 
  expansion 
  and 
  contraction 
  when 
  burned, 
  but 
  will 
  show 
  the 
  

   proper 
  relation 
  between 
  their 
  fusing 
  points, 
  and 
  the 
  glaze 
  will 
  not 
  

   fuse 
  much, 
  or 
  not 
  at 
  all, 
  below 
  the 
  temperature 
  at 
  which 
  the 
  brick 
  

   vitrifies. 
  

  

  In 
  the 
  first 
  place 
  it 
  is 
  of 
  course 
  necessary 
  that 
  the 
  brick 
  sliall 
  

   not 
  contain 
  an 
  excess 
  of 
  lime, 
  so 
  that 
  it 
  can 
  be 
  vitrified 
  without 
  

   fusing; 
  and 
  having 
  found 
  a 
  clay 
  of 
  the 
  right 
  kind, 
  it 
  then 
  remains 
  

   to 
  find 
  a 
  glaze 
  which 
  it 
  will 
  carry 
  without 
  causing 
  it 
  to 
  craze. 
  

  

  One 
  way 
  to 
  arrive 
  at 
  this 
  experimentally 
  is 
  to 
  take 
  a 
  clay 
  whose 
  

   rational 
  composition 
  is 
  known, 
  and 
  by 
  the 
  addition 
  to 
  it 
  of 
  different 
  

   quantities 
  of, 
  say, 
  quartz 
  sand, 
  feldspar 
  and 
  lime, 
  make 
  mixtures 
  

   which 
  will 
  show 
  considei'able 
  range 
  in 
  a 
  rational 
  composition. 
  Add- 
  

  

  