Full resolution (JPEG) - On this page / på denna sida - Shop Notes - To harden with cyanide of potassium - Blue Printing - To prepare blue print paper - Blue print frame - Blue printing
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480 SHOP NOTES.
To Harden with Cyanide of Potassium.
Heat the cyanide of potassium in a wrought iron pot until
cherry red, and keep it so by a steady fire, immerse the pieces
to be hardened from three to five minutes, according to their
size and degree of hardness required, then plunge into cold
water. Large pieces require more time than small ones, and
the longer the article remains in the cyanide the deeper the
hardening becomes. New cyanide gives the best color and
cyanide previously used for hardening produces a harder surface.
BLUE PRINTING.
To Prepare Blue Print Paper.
Dissolve two ounces of citrate of iron and ammonium in 8X
ounces of soft water. Keep this in a dark bottle. Also dissolve
1% ounces of red prussiate of potash in 8% ounces of water and
keep in another dark bottle. When about to use, mix (in a
dark place) an equal quantity of each solution in a cup and
apply with a sponge or a camel’s hair brush as evenly as pos-
sible on one side of white rag paper (such as used for envelopes).
Let it dry and put it away in a dark drawer. The paper must
not be prepared in daylight but when taking prints it may be
handled then, providing care is used to expose it as little as
possible to the light before it is put into the printing frame.
Blue Print Frame.
Make a strong frame similar to a picture frame having a
strong and thick glass. Make a loose back, from boards about
Yz inch thick, which is held into the frame by four suitable
catches so arranged that they press this back firmly and evenly
against the glass. The surface next to the glass should be
covered by three thicknesses of flannel in order to make a
cushion so that the prepared paper and the tracing are kept close
together when put in the frame.
Blue Printing.
The drawing must be made on transparent material, for
instance, tracing cloth or tracing paper. Place the tracing in
the frame with the side on which the drawing is made next to
the glass. Place the prepared side of the sensitive paper against
the back of the tracing. Put the loose back into the frame with
the padded side against the prepared paper, and fasten it up so
that both paper and tracing are kept firmly against the glass.
Expose to sunlight from three to six minutes, according to the
brightness of the sun. Take the sensitive paper out of the
frame and quickly put it into a tub of clean cool water and wash
it off, and the drawing will appear in white lines on blue
ground. Hang the print up by one edge so that the water will
run off, and let the print hang until dry.
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