I 
266 
THE lOUNG SCIENTIST. 
blance to the artistic ornainentatioii em- 
ployed by the aueient Egyptian artificers. 
Chemical analysis shows that the bluish 
tint so often to be seen in Etruscan glass 
is produced by cobalt, and this kind of 
manufacture is stated to have been usual 
in various important factories. 
The fineness of the ware produced in 
ancient Eome is said to have been mar- 
vellous. A glass-maker, who lived dur- 
ing the reign of the Emperor Nero, pro- 
duced glass vessels of wonderful light- 
ness, which commanded as high a price 
as about $150 each. Martial speaks of 
them as "glassy vapor." There is a 
specimen of this delicate kind of manu- 
facture in the Eouen Museum. It is a 
drinking vessel of white glass with a 
handle. Its circumference is 13 inches, 
and its height 4 inches, while its weight 
is said to be a fraction under 2 oz. 
The Blue Process. 
BY JAS. MACDONALD, M.E. 
HE introduction of the blue 
printing i^rocess for duplicat- 
ing drawings, has caused a de- 
cided change to be adopted in 
their preparation. The common practice 
now is to construct the drawing in fine 
hard pencil lines, and trace them without 
being " inked in " on tracing cloth or pa- 
per, as the drawing to be copied must be 
made on transparent material. 
The blue printing i^rocess is very sim- 
ple and comparatively inexpensive, and 
may be practiced by anyone who can 
]>r(>cure a piece of plate glass large 
enough to cover the drawing to be 
copied. The tracing should be made in 
good strong black lines. The figures, in- 
dicating dimensions, must also be put on 
plaiidy;the dimension and centre lines 
should always be broken or dotted, pre- 
ferably in red, so that they may be dis- 
tinguished from the other lines of the 
drawing, on the blue print. In working 
drawings, all the dimensions must be 
given in figures, as no men.surements can 
be made on the blue print. The paper 
shrinks or changes its shape so much 
when being washed, tliat it is no longer a 
duplicate of the original, so far as size is 
concerned. The tracing must be kept j 
clean, fiat and smooth to insure good ' 
work, as any creases or folds in the ma- • 
terial will be reproduced in the print. 
The kind of paper to be used in the blue | 
print, will depend on the use to which it 
is to be put. Almost any kind of paper 
may be used, so long as it is white ; but 
for copies of drawings that are intended 
for office use, to bo filed away for refer- 
ence, or that may be sent through the 
mails, it is advisable to have thin tissue 
paper. This will stand a moderate usag.e, 
and will fold into a small compass, and 
may be placed in envelopes if necessary, 
and filed. For prints that are to be 
used as working drawings in the shop, or 
on buildings, a thick heavy white paper 
is best. 
The chemicals necessary for preparing 
the paper and their proportions are as 
follows: 11 oz. citrate of iron and ajti- 
monia; 11 oz. red prussiate of potash. 
To be mixed with 16 oz. water. The iron 
and potash should be thoroughly dis- 
solved in the water', and the mixture 
filtered through bibulous paper. The 
operation should be performed in a daTk 
room. Keep the mixture from the light. 
To prepare the paper, it is laid flat on a 
table, and with a soft brush the surface 
is coated ^evenly with the chemical pre- 
paration, care being taken to avoid 
" streaking " or brush marks, as any un- 
evenness of this kind will show in the 
print. Colored lights, such as from a 
lamp or gas jet, will not affect the pre- 
paration, but it must be kept from the 
sun or electric light. To take the print, 
the prepared paper should be laid with 
the chemical side up on a flat soft 
cushion, which may be a thick blanket 
spread evenly on a table; on this the 
tracing is placed with the blank side next 
to the ]mper, and both covered with the 
glass plate. An exposure of from 4 to 
30 minutes, will be necessary according 
to the intensity of the sun light. If it re- 
ceives the direct rays of the sun, the 
paper will turn iron grey in color, after 
about four or five minutes, and then must 
be removed quickly. It may now be 
placed against , an inclined surface, and 
be thoroughly washed by directing a 
