Copies of drawings or parts representing details and measurements are
frequently needed for the office, pattern shop, machine and blacksmith
shop, etc. These copies are best made by printing on sensitized or
specially prepared paper, from tracings drawn on transparent cloth or
paper, as hereabove described. The original design may be guarded with
the utmost care for long preservation, but the blue prints, so called,
are for ready reference and use without much regard to the length of
time they are to be in existence.
The usual practice is to carefully trace from the drawing on transparent
cloth or paper an exact reproduction of it, filling in all detail
lettering and sizes or figured dimensions.
This tracing is fixed in a frame similar to a picture frame, with the
side on which the drawing is made next to the glass: 1, place the
sensitized side of the paper (which has been prepared previously)
against the back of the tracing; 2, fix soft padding against the back of
the paper and fasten it up so that both paper and tracing are compressed
firmly against the glass, permitting no creases or air spaces between
them.
[Illustration: Fig. 262.]
This should be done in a darkened room; 3, expose for three to six
minutes, according to the intensity of the sun; 4, take the sensitized
paper out of the frame and quickly wash well in clean running cool
water, and the drawing will appear in white lines on blue ground; 5,
hang the print up by one edge so that the water will run off and the
print will soon dry and be ready for use.