<s>
A	O
contact	B-Application
copier	I-Application
(	O
also	O
known	O
as	O
contact	B-Application
printer	I-Application
)	O
,	O
is	O
a	O
device	O
used	O
to	O
copy	O
an	O
image	O
by	O
illuminating	O
a	O
film	O
negative	O
with	O
the	O
image	O
in	O
direct	O
contact	O
with	O
a	O
photosensitive	O
surface	O
(	O
film	O
,	O
paper	O
,	O
plate	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
Commercial	O
contact	B-Application
printers	I-Application
or	O
process	B-Algorithm
cameras	I-Algorithm
usually	O
use	O
a	O
pump-operated	O
vacuum	O
frame	O
where	O
the	O
original	O
and	O
the	O
photosensitive	O
surface	O
are	O
pressed	O
together	O
against	O
a	O
flat	O
glass	O
by	O
a	O
grooved	O
rubber	O
mat	O
connected	O
to	O
the	O
vacuum	O
source	O
.	O
</s>
<s>
The	O
contact	O
copying	O
process	O
was	O
used	O
in	O
the	O
early	O
days	O
of	O
photography	O
and	O
sunlight-exposed	O
blueprints	B-Application
;	O
it	O
is	O
still	O
used	O
in	O
amateur	O
photography	O
,	O
silkscreen	O
printing	O
,	O
offset	O
printing	O
,	O
and	O
photochemical	O
machining	O
,	O
such	O
as	O
the	O
manufacture	O
of	O
Printed	O
circuit	O
boards	O
.	O
</s>
<s>
By	O
the	O
early	O
20th	O
century	O
,	O
blueprinting	O
(	O
producing	O
white	O
lines	O
)	O
or	O
diazo	B-Application
blue	B-Application
line	I-Application
printing	I-Application
used	O
contact-rollers	O
rather	O
than	O
flat-glass	O
exposure	O
.	O
</s>
<s>
Silkscreen	O
printing	O
and	O
photochemical	O
machining	O
originally	O
were	O
based	O
on	O
gum	O
bichromate	O
photosensitive	O
materials	O
,	O
where	O
exposure	O
to	O
intense	O
ultraviolet	B-Application
light	O
made	O
previously-soluble	O
gum	O
or	O
gelatin	O
colloids	O
insoluble	O
;	O
after	O
exposure	O
,	O
the	O
exposed	O
surface	O
was	O
washed	O
in	O
water	O
and	O
the	O
unexposed	O
coating	O
dissolved	O
,	O
leaving	O
the	O
hardened	O
gum	O
or	O
gelatin	O
to	O
resist	O
the	O
passage	O
of	O
the	O
silk-screen	O
ink	O
or	O
the	O
metal-etching	O
solution	O
.	O
</s>
<s>
The	O
contact	B-Application
copier	I-Application
is	O
used	O
for	O
duplication	O
of	O
negative	O
or	O
positive	O
prints	O
obtaining	O
what	O
are	O
called	O
contact	O
prints	O
,	O
that	O
is	O
,	O
to	O
reproduce	O
on	O
paper	O
or	O
film	O
,	O
a	O
photographic	O
negative	O
or	O
positive	O
of	O
exactly	O
the	O
same	O
size	O
of	O
the	O
original	O
.	O
</s>
<s>
The	O
negative	O
role	O
fits	O
the	O
body	O
,	O
the	O
lid	O
is	O
closed	O
applying	O
some	O
pressure	O
against	O
the	O
glass	O
to	O
prevent	O
blur	O
;	O
then	O
proceed	O
to	O
impress	O
photographic	O
paper	O
by	O
turning	O
on	O
the	O
interior	O
light	O
(	O
contact	B-Application
copier	I-Application
)	O
or	O
an	O
external	O
focus	O
,	O
in	O
the	O
last	O
case	O
,	O
usually	O
from	O
a	O
photographic	O
enlarger	O
.	O
</s>
<s>
In	O
the	O
process	O
of	O
whiteprint	B-Application
copying	O
,	O
(	O
essentially	O
a	O
diazotype	B-Application
process	O
)	O
,	O
a	O
dynamic	O
contact	B-Application
copier	I-Application
is	O
used	O
(	O
similar	O
to	O
the	O
manual	O
action	O
of	O
exposing	O
both	O
sheets	O
strongly	O
bonded	O
directly	O
to	O
the	O
sunlight	O
.	O
)	O
.	O
</s>
<s>
The	O
exposition	O
is	O
made	O
progressively	O
as	O
the	O
twin	O
rollers	O
pull	O
the	O
two	O
papers	O
together	O
(	O
original	O
and	O
copy	O
)	O
against	O
a	O
source	O
of	O
ultraviolet	B-Application
light	O
,	O
typically	O
a	O
powerful	O
black	O
light	O
lamp	O
.	O
</s>
<s>
The	O
original	O
plan	O
(	O
on	O
a	O
transparent	O
support	O
)	O
and	O
the	O
diazo	B-Application
paper	I-Application
are	O
introduced	O
,	O
in	O
perfect	O
contact	O
,	O
within	O
the	O
pinch	O
rollers	O
of	O
the	O
contact	B-Application
copier	I-Application
.	O
</s>
<s>
The	O
sensitized	O
paper	O
,	O
has	O
a	O
photosensitive	O
coating	O
-an	O
impregnation	O
of	O
diazo	B-Application
-	O
covering	O
the	O
surface	O
of	O
the	O
paper	O
.	O
</s>
<s>
In	O
screenprinting	O
it	O
is	O
normally	O
use	O
a	O
contact	B-Application
copier	I-Application
box	O
with	O
several	O
fluorescent	O
tubes	O
close	O
to	O
the	O
silk	O
frame	O
.	O
</s>
<s>
Usually	O
for	O
a	O
"	O
box	O
type	O
"	O
contact	B-Application
copier	I-Application
,	O
exposure	O
is	O
usually	O
not	O
more	O
than	O
one	O
minute	O
.	O
</s>
<s>
In	O
the	O
industrial	O
type	O
contact	B-Application
copiers	I-Application
with	O
actinic	O
lamp	O
placed	O
at	O
a	O
distance	O
,	O
exposure	O
time	O
can	O
be	O
about	O
20	O
minutes	O
.	O
</s>
<s>
The	O
photolith	B-Application
(	O
also	O
called	O
"	O
Art	O
"	O
)	O
is	O
placed	O
under	O
the	O
frame	O
against	O
the	O
emulsion	O
.	O
</s>
<s>
The	O
black	O
portions	O
of	O
photolith	B-Application
film	I-Application
does	O
not	O
let	O
light	O
into	O
the	O
relevant	O
parts	O
of	O
the	O
coated	O
silk	O
,	O
therefore	O
,	O
in	O
these	O
parts	O
Emulsion	O
will	O
not	O
heal	O
and	O
may	O
be	O
subsequently	O
washed	O
,	O
keep	O
in	O
mind	O
that	O
there	O
must	O
be	O
no	O
gap	O
between	O
the	O
photolith	B-Application
and	O
the	O
silk	O
,	O
to	O
achieve	O
that	O
purpose	O
any	O
element	O
with	O
enough	O
weight	O
may	O
be	O
used	O
to	O
press	O
the	O
silk	O
against	O
the	O
photolith	B-Application
(	O
or	O
a	O
vacuum	O
pump	O
in	O
professional	O
machines	O
)	O
.	O
</s>
<s>
In	O
CTF	O
offset	O
technology	O
,	O
a	O
photolith	B-Application
is	O
placed	O
in	O
direct	O
contact	O
with	O
the	O
printing	O
plate	O
and	O
pressed	O
with	O
an	O
opaque	O
lid	O
that	O
sometimes	O
has	O
a	O
vacuum	O
pump	O
that	O
helps	O
making	O
a	O
good	O
contact	O
.	O
</s>
<s>
The	O
plate	O
comes	O
coated	O
with	O
a	O
layer	O
of	O
photoresist	O
in	O
which	O
a	O
(	O
negative	O
)	O
inverted	O
image	O
is	O
formed	O
with	O
respect	O
to	O
the	O
original	O
photolith	B-Application
and	O
after	O
the	O
transfer	O
of	O
information	O
(	O
burning	O
)	O
it	O
's	O
accomplished	O
,	O
then	O
,	O
after	O
undergoing	O
a	O
developing	O
process	O
,	O
the	O
plate	O
will	O
be	O
ready	O
to	O
be	O
used	O
in	O
an	O
offset	O
printer	O
.	O
</s>
<s>
The	O
process	O
shares	O
some	O
fundamental	O
principles	O
with	O
the	O
photographic	O
processes	O
,	O
since	O
the	O
pattern	O
engraved	O
on	O
the	O
plate	O
is	O
generated	O
by	O
exposure	O
to	O
light	O
with	O
an	O
image	O
created	O
in	O
a	O
contact	B-Application
copier	I-Application
using	O
an	O
optical	O
mask	O
.	O
</s>
<s>
The	O
contact	B-Application
copier	I-Application
is	O
used	O
today	O
,	O
particularly	O
in	O
the	O
areas	O
hobbyist	O
,	O
for	O
the	O
photoengraving	O
of	O
prototype	O
printed	O
circuit	O
boards	O
(	O
PCBs	O
)	O
before	O
being	O
sent	O
to	O
production	O
(	O
artisanal	O
creation	O
)	O
.	O
</s>
<s>
Substantially	O
similar	O
to	O
the	O
contact	B-Application
printer	I-Application
used	O
in	O
photography	O
,	O
this	O
variant	O
usually	O
uses	O
ultraviolet	B-Application
lamps	O
to	O
impress	O
a	O
copper	O
base	O
specifically	O
pre-sensitized	O
.	O
</s>
<s>
Burned	O
by	O
exposure	O
to	O
light	O
parts	O
reproduce	O
patterns	O
drawn	O
on	O
a	O
transparent	O
photolith	B-Application
film	I-Application
on	O
a	O
pre-sensitized	O
plate	O
(	O
epoxy	O
or	O
Bakelite	O
)	O
.	O
</s>
<s>
Photolith	B-Application
film	I-Application
printed	O
parts	O
(	O
usually	O
black	O
)	O
,	O
inserted	O
between	O
the	O
light	O
source	O
and	O
the	O
pre-sensitized	O
plate	O
,	O
protect	O
the	O
varnish	O
from	O
the	O
UV	O
.	O
</s>
