SILVERING  AND  GILDING  OF  GLASS. 
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of  silver.  The  quantity  of  fluid  required  to  silver  a  glass  of  226 
square  centims.  was  280  cub.  centims.,  containing  1170  milligrms. 
of  silver,  so  that  1170 — 49  —1121  milligrms.  of  silver  are  thrown 
down  in  the  fluid  and  on  the  walls  of  the  vessel ;  this  must  be 
collected,  and  again  converted  into  nitrate  of  silver,  and  some  loss 
is  unavoidable. 
When  silvered,  the  glass  plate  is  taken  out  of  the  fluid,  washed 
with  warm  distilled  water,  and  dried  in  a  warm  place.  Care 
must  be  taken,  in  removing  and  washing  the  plate,  not  to  injure 
the  silver  coat  with  the  fingers,  as  otherwise  the  water  penetrates 
by  capillary  attraction  through  the  injured  spot,  and  separates 
the  coat  of  silver  from  the  glass.  When  dried,  the  silver  ad- 
heres so  strongly  to  the  glass  that  it  can  hardly  be  rubbed  off 
with  the  finger.  It  forms  a  very  beautiful,  somewhat  opalescent 
mirror,  which  may  be  converted  into  a  perfect  silver  mirror  by 
careful  polishing  with  fine  rouge  and  velvet.  A  good  deal  depends 
on  the  cleaning  of  the  glass  in  the  production  of  perfect  mirrors. 
The  distance  between  the  bottom  of  the  vessel  and  the  surface 
of  the  glass  must  be  exactly  equal  throughout,  as  otherwise  the 
thickness  of  the  coat  of  silver  will  be  unequal,  and  the  places 
where  it  is  thinnest  will  appear  darker  than  the  rest.  The  small- 
est bubble  of  air  also  will  cause  a  small  vacancy  in  the  coating, 
and  the  author  has  found  it  advantageous  to  moisten  the  surface 
of  the  glass  in  the  first  place  with  alcohol,  as  this  displaces  the 
adherent  stratum  of  air  more  readily  than  water. 
When  placed  at  the  bottom  of  the  vessel  the  glass  plate  is  just 
as  completely  coated,  but  the  whole  of  the  silver  in  the  solution 
is  precipitated  upon  it  in  the  form  of  a  gray  powder,  which  ad- 
heres so  strongly  that  it  can  only  be  got  rid  of  by  mechanical 
means,  which  endanger  the  mirror  itself.  The  cost  is  also  greatly 
increased. 
Before  putting  it  into  a  frame,  the  dry  mirror  is  warmed  a 
little,  and  coated  with  a  thin  colorless  varnish.  For  this  purpose 
a  solution  of  dammara  resin  in  alcohol  is  very  good. 
Gcilding  of  Grlass. — Glass  can  only  be  permanently  and 
brilliantly  gilt  with  the  assistance  of  heat.  Gilding  effected  in 
the  cold  is  of  beautiful  color  and  lustre,  but  does  not  adhere,  and 
detaches  itself  from  the  glass  by  washing  with  water. 
The  gilding  fluid  is  prepared  by  dissolving  pure  gold  in  nitro- 
