VARIETIES. 
279 
I)  a  t  i  c  t  i  e  s  ♦ 
Preservation  of  Photographic  Proofs  on  Paper.  By  M.  Gaudinet. — The 
author  was  led  to  this  process,  not  by  chance,  but  by  an  attentive  examina- 
tion of  what  was  produced  in  effaced  proofs,  in  which  the  design  was  not 
destroyed,  but  only  disguised  by  a  colored  layer  spread  uniformly  over  its 
surface,  and,  according  to  circumstances,  either  on  the  surface  of  the 
paper,  or  on  the  adjacent  layers.  He  compares  the  annihilation  of  the 
image  in  this  latter  case,  to  what  is  produced  when  we  place  under  a  de- 
sign drawn  on  tracing  paper,  a  sheet  of  a  dull  color.  Seeing  how  this 
colored  layer  is  produced  in  both  cases,  and  understanding  then  why  the 
proof  on  paper  was  altered,  whilst  those  on  glass  were  preserved,  he  thought 
that  if  Hte  could  succeed  in  rendering  the  paper  impermeable,  at  the  same 
time  retaining  its  color  and  its  semi-transparency,  he  would  have  solved 
the  problem.  For  that  purpose,  he  employed  a  process  which  he  has 
used  since  1855  for  making  troughs  of  card-board  instead  of  the  glass  or 
porcelain  troughs  used  in  photography.  The  following  is  his  mode  of 
operating : — 
"  I  dissolve/'  he  says,  "  a  certain  quantity  of  gutta  percha  of  commerce 
in  benzine  Colas ;  I  decant  at  the  end  of  a  few  days,  so  as  to  have  only  the 
clear  part.  I  plunge  my  paper  into  this  solution,  sheet  by  sheet,  and  re- 
move  it  almost  immediately  ;  then  suspending  it  by  one  corner,  I  allow  it 
to  dry.  I  afterwards  take  these  leaves,  which  contain  between  their  fibres 
a  sort  of  dust  of  gutta  percha,  but  not  a  varnish,  and  I  hold  them  one  by 
one,  before  a  good  fire.  All  the  grains  of  gutta  percha  then  unite  and 
cover  entirely  the  fibres  of  the  paper,  forming  an  almost  impermeable  in- 
ternal varnish. 
"  I  albumenize  this  paper,  which  has  lost  nothing  of  its  transparency, 
(albumen  100,  rain  water  25,  chloride  of  sodium  6.)  I  leave  it  to  dry,  and 
sensitize  with  a  solution  of  15  per  cent,  of  crystallized  nitrate  of  silver. 
I  drain  and  dry  before  a  gentle  fire  ;  I  take  the  positive  proof  under  the 
cliche  as  with  ordinary  paper,  and  I  fix  with  hyposulphite  of  soda,  of  10 
or  15  per  cent.  ;  but  this  operation  is  abridged,  so  that  the  proof  is  fixed 
after  a  few  minutes,  as  with  proofs  on  glass,  and  of  a  very  fine  sepia  aspect. 
If  we  wish  to  strengthen  with  chloride  of  gold,  it  is  done  in  the  ordinary 
way,  nothing  preventing  this  operation. 
"  The  washings,  instead  of  lasting  from  12  to  24  hours,  may  be  com- 
pleted in  a  quarter  of  an  hour,  and  the  proof  is  of  admirable  transparency, 
the  paper,  moreover,  retaining  all  its  whiteness. — London  Chemist,  Oct., 
1858,  from  Comptes  Bendus,  August  2,  1858. 
