St. Tammany farmer. [volume] (Covington, La.) 1874-current, 1886-10-16
PHoTo.PRlNTING.
PhotOgravure for Book Illustrations and
Zinco-Types for Newspaper Work.

Photogravure for Book illustrations and
Zinco-Types for Newspaper Work.
| The use of Photographic negative
in connection with photographic sur
face has become of such importance
for almost every sort of illustrated
work, from the business circular to the
finest books of art, that the name OF
Poitevin, the French inventor and real
father of the process, deserves to be
better known than it is. Louis Ale
phonse Poitevin was born at Contains,
in the Department Of the Santhe.
France. in 1919. His bent towards APP
piled chemistry led him early to the
Ecole Centrale. i'm Paris, where he de-
voted himself almost entirely to chem
zeal and mechanical studies. leaving
the school in 1913 with the diploma Of
civil engineer. His first appointment
was that of chemist in the national
salt works in the east of France, in
which capacity he introduced many
Improvements in the processes and
machinery used. and also in the manu-
! facture of potash. sulphuric acid. etc.
When photography came upon the
| world rs scientific curiosity, Poitevin's
taste for chemistry led him to expert
ment with the new toy. and in 1913 he
3 published the fact that it was possible
to produce an electro deposit of cop
: per upon the whites of the daguerreo-
type image. His work in this direction
{ led to the discovery of a method of pho
to-chemical engraving upon metallic
plates coated with gold or silver, for
which he received the medal of the
Societe Encouragement des Arts.
Soon afterwards he began work upon
the study of the action of light upon
| bichromated gelatine. He first applied
himself to the production of molls in
relief. and patented in 1855 his hello
plastic process. which consisted in pre-
pairing Il film of gelatine. which, after
sensitizing by means of biehromate of
potassium, was exposed to light under
negative When cold water was APP
piled, the parts Enacted upon by
light swelled up and so formed an
image in relief from which n mold in
plaster or other suitable material could
be taken.
Ills HUM atCIilcseiuClt Was lIlG
process. He discovered that the sur
face of the bichromated gelatine film
after exposure to light became re-
pellent of water. while it permitted
greasy ink to adhere. In 1856 he
established workshop for the pro-
duction of pictures by this process.
Some of his early plates are in the
possession of Mr.. Edward Bierstadt, of
this city. and compare favorably with
much work of to-day. Poitevin was,
however, too much engrossed in in
vention to prosper in business, and he
sold out the shop to Lemercier. who
still carries it on, and turned his at
tcntion again to experiments. In 1862
h perfected system of carbon print
ing. from which the present processes
are derived. He also published re-
searches in connection with the action
of light upon various salts of iron. The
Due de Luynes awarded him the prize
offered for advances in applied science,
and at the exhibition of 1873 he was
adiudged gold medal and an honor
arium of seven thousand francs in
recognition of his services. He died at
Contains. March 4, 1892.
Some of the best work done in this
country with processes growing out of
Poiteyin's invention is that known
under the general head of photo
gravure, which is printed directly from
an etched plate. The plate is covered
with sensitive film and afterwards
etched, the acid acting where the light
coming through negative has fallen.
From such plate. using Il copper-plate
press. the New York company which
makes speciality of this work pro-
duces very beautiful results. For fine
books. where cheapness is not sought.
the photograyure answers the purpose
admirably. for any number of impress
sions can be taken. The same company |
also uses the gelatine plate process, as
modified by Mr.. c. T. Roche. Some OF |
the large plates and reproductions of |
sepia sketches. done in this way, are |
admirable specimens of the art ut its |
best.
For purposes of newspaper illustra-
ton. especially in colors, zincography |
is much used in Europe and, to a smaRs
extent. in this country. Zinc plates are
coated with an asphaltum film and ex-
posed under a negative or drawing from
ten to sixty minutes. Asphaltum in
certain conditions is sensitive to light.
Where light acts acid can penetrate to
the plate, and it is etched in the usual
manner. When it is desired to print
in colors, negative is prepared for
each color, one allowing no light to
pass except for yellows, another reds,
etc. Many German and French news
papers are illustrated by this process.
The colored plates in the last Christmas
number of the Paris Figaro, so largely
sold in this country, were photo-zinco.
types.-N T. Post.
PROGRESS OF TELEGRAPHY.
without a Break Between