19

BLUE PAPER PRINTING.
A Valuable Process for the Duplication of Draw-
ings and Engravings.
THE
process of making blue prints is a valuable and
important part of the knowledge that a draftsman
must possess,
and the
process
is so simple that the
method should be
put to much
greater use than at pres-
ent, even though it be used a good deal for the produc-
tion of
working drawings for shop use and for the dupli-
cation of specifications, details, contracts, etc. The blue
printing process
is capable of being carried much further
towards perfection than is practiced at present, when its
use is
chiefly limited to the production of copies of draw-
ings which show white lines on a blue ground. Such
drawings are tiresome to the
eye,
and do not impress the
workman as favorably as blue or black lines on a white
ground. •
The usual
process of. making blue prints, is to coat one
side of the
paper, using for the
purpose a brush or a
sponge, with a mixture consisting of one drachm of the
red
prussiate, and one and one-half drachms of the am-
monia citrate of iron, dissolved in about one ounce of
water. This amount of solution will be sufficient to
coat several large sheets of
paper,
but it will not keep a
great while after being coated. The surface is yellow
when first coated, and after a week or so will have turned
to a dirty greenish color. It can be used in this condi-
tion, but makes inferior prints. It is better to make
up
some fresh solution, for it only takes a few minutes to dry
the paper ready for use after the coating has been spread
on. Then a sheet of it is put under the tracing, and ex-
posed to the sunlight under a sheet of thick glass, or in
a regular frame for making blue prints. After exposing
until the
parts of the
paper
not protected from the sun-
light have turned to a kind of “greenish granite” color,
the print is removed and washed in clear water until the
yellow color stops coming from it. Then the print is
hung up to dry.
In order to make a blue print with blue lines on a
white ground, two methods are open.
The first is to
make a print which
may
be called a “negative,” and then
to make the blue line prints from that, instead of from
the drawing itself. The reader can readily see that if a
print from a transparent sheet with
opaque lines thereon
will give a copy
that is
opaque
with
transparent lines,
then by taking another print from the first print, there
will be opaque lines on a transparent ground again,
similar to the original drawing. But there is one draw
back to this method, which is fatal to its success. That
is, the blue print which is made from the original will
not work when used as a negative because being of blue
color, the of light which shine through that color
will affect the sensitive sheet fully as quickly as the
rays
which shine through the
transparent or white
paper.
In fact, blue is one of the actinic colors, and likewise one
of the most activelyactinic of them all. Now, if the print
taken for a negative could be black, yellow, red, or any
of the non-actinic colors, there would be no more trouble
in printing a blue print from it than there is in printing
one from the original tracing.
It is in order, therefore, to look around for some means
of making a print which will be non-actinic. To this
end, it is best to get a sheet of “
silver paper” from
a photographer, or what is easier, get him to make a print
of the tracing on silver paper. Then, after that is
“
toned ”
and finished, it can be used as a negative for
the making of as many blue-line prints as may be de-
sired. If
any
reader of this
paper desires fuller in-
formation as to how the silver paper
is prepared and
toned, he can procure the information by writing to the
editor, who will take pleasure in publishing in full com-
plete directions for making and using silver paper, or
any
of the other kinds mentioned in this article.
The other way of making a blue line print, or,
in fact,
one other way, is to make up a kind of blue print paper
which will turn blue only where the
sunlight does not
hit. This is a little different from the first kind of
paper
described, and the difference is that this kind is charged
with chemicals which the sunlight has the power of de-
stroying the color thereof, instead of setting the color,
as in the case of the ordinary blue
paper already de-
scribed. This matter, too, will be more fully described
if any reader requests the information, with sufficient
interest to write therefor.
For the
present, it will be sufficient to state that the
paper
is prepared by mixing together three
solutions,
then mixing the three into one when ready for
use,
and
spreading it on the paper as if for a simple blue print-
The three solutions are as follows :
Gum arabic... 6 drachms
Water 30 drachms
Ammonia citrate of iron .
4 drachms
Water 8 drachms
Perchloride of iron 2.5 drachms
Water 5 drachms
As these things will keep separate, they can be mixed
in larger quantities, for instance, taking ounces for
drachms, then the
quantity that is to be used at one time
can be taken of each, let it be in drachms, half drachms,
or minims. The paper will also keep well after it is sen-
sitized, so that a quantity may be made up at one time,
and kept from the light till needed. The reason that
this kind of paper will keep, while the other will
not, is
because the common paper turns upon exposure to the
light, while this kind will not
turn, even in the develop-
ing solution, if it is exposed to light. The paper is
printed in the usual
manner,
then it is floated upside
down on a solution of
Potassium ferocyanide 1 ounce
Water 4 ounces
The paper must be floated on top of the mixture be-
cause it will stain the back of the print if any of it
gets
thereon. After the lines get blue
enough, as may be de-
termined by turning up a corner of the
paper occasion-
ally , it should be removed from the “developer” and
floated on clean
water, which will at once
stop the
pro-
cess of turning any darker. If there be
any blue
spots
left on the paper where they don’t belong; i. e., except on
the lines, they can all be cleared off by putting the sheet
of paper
in (no need to bother with
putting on top this
time) a solution of eight parts muriatic, or three
parts
sulphuric acid, with 100
parts of water. After the blue
spots have disappeared, wash well in
water, dry, and a
print with rich blue lines on a white ground is the result.
This kind of print, the “blue positive,” may be
colored,
something which cannot be done with an ordinary blue
print.
There are other ways by which positive prints may be
made, in black lines on a white
ground, and
by using
different colored
paper to begin with, most effective prints
may
be made. The manner of making
“
black
posi-
tives,” also of making them on cloth, will be
given upon
request therefor. —
The Tradesman.
246 THE SOUTHERN ARCHITECT.