﻿648 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  this. 
  Such 
  substances 
  go 
  under 
  the 
  collective 
  name 
  of 
  grogs, 
  

   and 
  may 
  include 
  sand, 
  ground 
  bricks, 
  coke, 
  graphite, 
  etc. 
  

  

  Grogs 
  serve 
  to 
  prevent 
  cracking 
  in 
  both 
  burning 
  and 
  drying. 
  

   They 
  also 
  tend 
  to 
  prevent 
  the 
  blistering 
  of 
  easily 
  fusible, 
  ferrugin- 
  

   ous 
  clays 
  when 
  fired 
  hard. 
  They 
  furthermore 
  add 
  to 
  the 
  

   porosity 
  of 
  the 
  ware 
  and 
  thus 
  facilitate 
  the 
  escape 
  of 
  the 
  moisture 
  

   in 
  drying 
  and 
  in 
  the 
  early 
  stages 
  of 
  burning, 
  and 
  also 
  enable 
  the 
  

   product 
  to 
  withstand 
  sudden 
  changes 
  of 
  temperature. 
  Grogs 
  may 
  

   however 
  act 
  as 
  fluxes 
  at 
  high 
  temperatures; 
  the 
  finer 
  the 
  grog, 
  the 
  

   more 
  intense 
  will 
  be 
  this 
  action. 
  

  

  If 
  the 
  grog 
  is 
  to 
  decrease 
  the 
  shrinkage 
  in 
  drying 
  and 
  burning, 
  

   it 
  must 
  not 
  be 
  added 
  in 
  the 
  form 
  of 
  powder, 
  but 
  as 
  grains, 
  and 
  

   even 
  in 
  this 
  case, 
  the 
  grains 
  must 
  not 
  exceed 
  a 
  certain 
  size, 
  other- 
  

   wise 
  they 
  will 
  only 
  serve 
  to 
  increase 
  the 
  tearing 
  of 
  the 
  wares 
  in 
  

   drying 
  and 
  burning. 
  The 
  cause 
  of 
  this 
  lies 
  in 
  the 
  fact 
  that 
  the 
  

   grog 
  itself 
  does 
  not 
  as 
  a 
  rule 
  shrink, 
  and 
  if 
  in 
  any 
  one 
  place 
  the 
  

   clay 
  substance 
  shrinks 
  to 
  such 
  an 
  extent 
  that 
  it 
  can 
  no 
  longer 
  sur- 
  

   round 
  the 
  particle 
  of 
  grog, 
  the 
  latter 
  will 
  act 
  as 
  a 
  wedge, 
  tearing 
  

   the 
  grains 
  apart, 
  and 
  a 
  crack 
  will 
  be 
  started. 
  If 
  this 
  action 
  shows 
  

   itself 
  in 
  the 
  raw 
  material, 
  it 
  can 
  be 
  eliminated 
  by 
  the 
  addition 
  

   of 
  powdered 
  grog. 
  When 
  this 
  is 
  not 
  possible, 
  the 
  coarse 
  particles 
  

   must 
  either 
  be 
  removed 
  or 
  reduced 
  by 
  crushing. 
  

  

  Sand. 
  This 
  is 
  the 
  form 
  of 
  grog 
  commonly 
  found 
  in 
  nature 
  and 
  

   most 
  frequently 
  used 
  artificially. 
  Sand 
  as 
  it 
  occurs 
  in 
  nature 
  is 
  

   commonly 
  composed 
  of 
  mineral 
  grains, 
  representing 
  a 
  variety 
  of 
  

   species. 
  Pure 
  quartz 
  is 
  of 
  course 
  the 
  most 
  desirable, 
  but 
  quartz 
  sands 
  

   generally 
  contain 
  impurities, 
  which 
  at 
  times 
  may 
  be 
  sufficient 
  to 
  pre- 
  

   vent 
  their 
  use 
  for 
  certain 
  purposes. 
  Clay 
  impurities 
  might 
  be 
  

   washed 
  out, 
  but, 
  as 
  others 
  like 
  feldspai*, 
  calcite, 
  etc., 
  could 
  not 
  be 
  

   removed 
  by 
  washing, 
  the 
  best 
  way 
  to 
  obtain 
  clean 
  quartz 
  sand 
  is 
  

   to 
  crush 
  up 
  vein 
  quartz, 
  or 
  quartzite. 
  An 
  advantage 
  connected 
  

   with 
  this 
  type 
  of 
  sand 
  is 
  that 
  the 
  grains 
  have 
  an 
  angular 
  structure, 
  

   whereas 
  grains 
  of 
  natural 
  sand, 
  being 
  usually 
  of 
  sedimentary 
  origin, 
  

   have 
  a 
  rounded 
  form, 
  and 
  will 
  not 
  interlock 
  as 
  well. 
  In 
  addition 
  

  

  