398         CLEANING  AND  PRESERVATION  OF  ENGRAVINGS. 
stowed  on  paintings  which  often  command  public  admiration, 
or  are  the  so-called  gems  of  an  exhibition. 
In  commencing  to  restore  an  engraving,  some  attention  must 
be  given  to  the  kind  of  injury  it  has  suffered.  A  general  brown 
color,  more  or  less  deep,  resulting  from  atmospheric  action  only, 
is  the  least  possible  change.  Spots  and  stains  caused  by  ink, 
colored  fluids,  oil  or  insects  must  be  first  treated,  and  all  pen- 
cil marks  removed  by  india-rubber  or  bread  crumbs.  A  fluid 
acid,  obtained  by  dissolving  one  ounce  of  crystals  of  oxalic  acid 
in  one-fourth  of  a  pint  of  warm  water,  may  be  used  for  applica- 
tion to  all  stains,  and  the  paper  should  be  wet  with  it  thoroughly 
where  spots  of  any  kind  exist.  Excepting  in  a  few  cases,  this 
acid  will  not  cause  the  removal  of  stains  immediately,  but  gene, 
rally  it  combines  with  the  bases  of  them,  and  they  are  removed 
by  subsequent  steps  ;  the  thorough  wetting  should  be  done  a  few 
hours  before  proceeding  to  clean  the  engraving. 
To  facilitate  handling  and  for  the  protection  of  the  edges  of 
the  paper,  a  piece  of  millinet,  or  the  stiff  open  fabric  formerly 
sold  for  ladies'  skirts,  should  be  roughly  sewed  around  one  stick 
at  each  end,  so  as  to  form  an  apron,  like  a  chart  attached  to  two 
rollers,  the  cloth  of  which  must  be  an  inch  larger  than  the 
largest  print  to  be  handled.  From  one  to  ten  prints  of  even 
large  size  may  be  cleaned  at  one  time,  after  they  have  been  wet 
on  their  spotted  parts  with  the  acid,  and  evenly  spread  on  the 
apron,  so  as  to  allow  of  the  immersion  of  the  whole  in  water. 
A  tub  of  the  ordinary  size  will  allow  prints  of  considerable  sur. 
face  to  become  immersed,  but  the  most  desirable  resort  is  a 
common  bathing  vessel,  so  nearly  filled  with  warm  water  that 
the  bent  paper  supported  by  the  open  texture  can  rest  on  the 
bottom  and  sides,  where  it  should  be  allowed  to  remain,  with  oc- 
casional raising  of  it,  and  moving  it  by  means  of  the  stick 
handles,  from  twelve  to  twenty-four  hours. 
On  the  first  trial  a  degree  of  alarm  will  be  felt  in  the  case  of 
a  highly-prized  favorite  at  this  seeming  careless  treatment ;  but 
it  must  be  borne  in  mind  that  paper  is  a  firmly  felted  mass  of 
short  fibres  which  may  be  soaked  in  various  fluids  for  weeks  and 
resist  all  diluted  acids  and  most  chemical  agents  for  a  long  time 
wet,  if  not  exposed  to  mechanical  abrasion  by  touch  or  rapid 
motion.    The  strong  paper  of  engravings  absorbs  much  air, 
