Production of Coloured Photographic Pictures by Means of Diazo and Tetrazo Compounds.
Year: 1894

page_text: Date of Application, 2nd June, 1894
Complete Specification Left, 1st Mar., 1895-Accepted, 13th Apr., 1895
[Communicated from abroad by THE ACTIEN GESELLSCHAFT FÜR
ANILIN FABRIKATION, of Berlin, in the Empire of Germany, Chemical
Manufacturers.]
Production of Coloured Photographic Pictures by Means of Diazo
and Tetrazo Compounds.
I, CHARLES DENTON ABEL, of No. 28 Southampton Buildings, Chancery
Lane, in the County of London, Consulting Engineer and Chartered Patent
Agent, do hereby declare the nature of this invention to be as follows:-
In the German Patent No. 56606 of 2nd September 1890 the production of
coloured pictures by means of primuline and bases of a similar constitution is
described. The pictures were obtained by exposing the diazo body under a
positive to the light and subsequently combining those parts of the diazo body
which were not decomposed by the action of light with an amine or phenole of
the dye stuff.
This process however could up to the present time not find
application for several reasons.
any technical
In the first instance the decomposition products of the yellow diazo bodies were
not incoloured and in consequence thereof it was impossible to obtain pictures with
a pure white ground; moreover this process yielded only a limited number of
shades and it was quite impossible to produce deeper shades, as for instance blue
and black.
My foreign correspondents have now discovered that all diazo bodies are more
or less sensible to light and therefore may be used under suitable conditions for
the production of coloured pictures.
This fact is not only interesting from a scientific point of view but is also of
great technical value because the great number of diazo compounds enables my
foreign correspondents to produce pictures not only of greater perfection than was
possible by means of the so called primuline process, but also to produce with
regard to the variety and solidity, results, which by no means could be obtained
by the aforesaid process.
This invention may be generally carried out in two different ways.
1. The diazo compound may be exposed in or on a layer (paper, wood &c.)
under a positive and the picture developed by subsequent treatment with an amine
or phenole.
2. The diazo compound may be exposed under a negative and the decomposition
product of the diazo body (as for instance naphthol if diazo-naphthaline is used)
may be combined with a diazo-compound to form in the usual manner azo dyes.
The following general directions may be given for the carrying out of the
invention. The duration of the exposure to light depends on the nature of the
diazo compound used, that is to say, on its greater or less capability of being
decomposed by light; the tetrazo compound of diamidostilbene for instance is
already decomposed by an exposure of a few minutes; the tetrazo bodies of
diphenyl or diphenol ethers are somewhat more stable. On the other hand several
diazo compounds must be exposed half an hour or more, in order to complete the
▸ decomposition.
In the method mentioned under 1 it is further advantageous for the production

page_text: of good pictures with a pure white ground to expose, after the decomposition of
the diazo compound, the translucid underlayer with its back to the light for a short
time. According to the nature of the diazo compound employed, this may be
directly fixed on the layer (paper, wood &c.) or the layer may be first made to
imbibe the amine to be diazotised, and by means of nitrous acid the latter be
afterwards transformed into the diazo compound.
If the method mentioned under 1 is followed the diazo body, such as it is
obtained by the diazotation of the amines, may be used directly; or the diazo
compound or its salts may be separated, and by redissolving the latter, the
sensitising solution be produced. If the diazo body allows of the separation, the
latter process is more advantageous, because with a purified diazo solution better
results are obtained.
The layer rendered sensitive with the diazo-solution may generally be used in a
dry state and therefore may be dried at a low temperature in a dark-room. Of
course, when working according to the method mentioned under 2 a certain amount
of humidity is required in order to enable the transformation of diazo-compound
into phenol compound to be effected.
The following examples may in detail illustrate the manner in which this
invention can be practically carried out.
1. a-naphthylamine disulpho acid & is diazotised in the well known manner and
the diazo body is filtered off; the diazo-compound is dissolved in as much cold
water and ice as will form a saturated solution, which may serve as sensitising-
solution.
The paper is soaked for about two minutes in the above mentioned solution, and
then dried in a dark room at a low temperature.
The sensitive layer is then exposed about 15 minutes under a positive to the
In order to produce a good picture it is advantageous to expose the paper
with the back for a short time to the light.
Sun.
For the development, a cold solution of 5 grammes a-naphthol in 500 c.cm. water
and 3 ccm. caustic soda lye of 1.39 spec. gr. is used.
In this way a crimson coloured picture is obtained.
2. In an analogous manner the paper is saturated with the diazo compound of
cumidine and exposed during about 40 minutes. By subsequent development
with a-naphthol a vermilion red picture results.
3. If the paper is saturated with tetrazo diphenyl, and exposed about 10 minutes
to light, it yields a blue-red picture with ẞ-naphthol.
4. If in the Example 3 the B-naphthol is replaced by the a₁ aд amidonaphthol-
monosulpho acid S a blue picture is obtained.
5. A blue-black picture is produced by developing the paper rendered sensitive
by tetrazodiphenyl, with y amidonaphtholsulpho acid.
The following example will illustrate the second method namely the production
of the phenol on the layer and development with a diazo-body.
6. The paper is rendered sensitive with a solution of a-diazo-naphthaline chloride
prepared in the well known manner. Whilst still humid, the paper is exposed for
from 10 to 15 minutes to the dispersed day-light. The picture is then developed
by treatment with a 10 p.c. solution of the sodium acetate free of water. This
solution dissolves the diazo-compound not decomposed, which enters into reaction
with the formed a naphthol, yielding in this way a brown picture.
7. If in the before mentioned example the a-naphthylamine is replaced by
B-naphthylamine a red picture is obtained.
8. In the Examples 6 and 7 the same diazo body was used for the development
of the picture as had served for the formation of the phenol, but the development
may also be effected by means of another diazo-compound. In this case it is only
necessary to remove in a suitable manner as for instance, by washing the
undecomposed parts of the diazo body first used.
If in the Example 7 the picture is developed with a solution of tetrazodiphenol-
ether, instead of diazonaphthaline, a violet picture is produced.

page_text: It may be finally mentioned that the pictures obtained in the above described
manner may be toned or may be rendered fast by a treatment with metallic salts.
and dow of Tune 1894
ABEL & IMRAY,
Agents for the Applicant.
Production of Coloured Photographic Pictures by Means ofI Diazo
and Tetrazo Compounds.
I, CHARLES DENTON ABEL, of No. 28 Southampton Buildings, Chancery
Lane, in the County of Loudon, Consulting Engineer and Chartered Patent
Agent, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement :-
In the Specification No. 7453 of 1890 the production of coloured pictures by
means of primuline and bases of a similar constitution is described. The pictures
were obtained by exposing the diazo body under a positive to the light, and
subsequently combining those parts of the diazo body which were not decomposed
by the action of light with an amine or phenole of the dyestuff.
My foreign correspondents have now found a new process for the production of
coloured pictures by means of diazo compounds. According to this process, the
diazo body is exposed to light under a negative and the decomposition products
formed by the action of light, for example naphthol, when diazo naphthaline is
exposed, are then combined with diazo bodies.
The new process may be regarded as the inversion of that described in the
Specification No. 7453 of 1890 above referred to. In the primuline process, the
diazo compound, which is not transformed by the action of light yields the image,
whereas in the new process now described the products, transformed by the action
of light, serve to produce the image.
The following general directions may be given for the carrying out of the invention.
The duration of the exposure to light depends on the nature of the diazo
compound used, that is to say, on its greater or less capability of being decomposed
by light the tetrazo compound of diamidostilbene, for instance, is decomposed by
an exposure of a few minutes; the tetrazo bodies of diphenyl or diphenol-ethers
are somewhat more stable. On the other hand, several diazo compounds must be
exposed half an hour or more, in order to complete the decomposition.
According to the nature of the diazo compound employed, this may be directly
fixed on the layer (paper, wood &c.) or the layer may be first made to imbibe the
amine to be diazotised, and by means of nitrous acid the latter may be afterwards
transformed into the diazo compound.
In the first case, the diazo body, such as it is obtained by the diazotation of the
amines, may be used directly; or the diazo compound or its salts may be separated,
and, by redissolving the latter, the sensitising solution may be produced. If the
diazo body allows of the separation, the latter process is the more advantageous,
because, with a purified diazo solution, better results are obtained.
Of course, a certain amount of humidity in the sensitive layer is required in
order to enable the transformation of the diazo compound into phenole compound
to be effected; generally the humidity which remains in paper, for instance, when
it is dried at ordinary temperature, is sufficient.
The following examples may in detail illustrate the manner in which this
invention can be practically carried out.
1. The paper is rendered sensitive with a solution of a-diazo naphthaline
chloride prepared in the well known manner.

page_text: Whilst still moist, the paper is exposed for from 10 to 15 minutes to the dispersed
day light. The picture is then developed by treatment with a 10 per cent. solution
of the sodium acetate which has been rendered as free from water as possible.
This solution dissolves the diazo compound not decomposed, which enters into
reaction with the a-naphthol formed, yielding in this way a brown picture.
2. When in the before mentioned example the ẞ-naphthylamine is substituted
for the a-naphthylamine, a red picture is obtained.
3. In the Examples 1 and 2 the same diazo body was used for the development
of the picture as had served for the formation of the phenole, but the development
may also be effected by means of another diazo compound. In this case, it only
necessary to remove in a suitable manner, as, for instance, by washing, the
undecomposed parts of the diazo body first used.
If in the Example 2, the picture is developed with a solution of tetrazo-diphenol-
ether instead of diazonaphthaline, a violet picture is produced..
It may be finally mentioned that the pictures obtained in the above described
manner may be toned or may be rendered fast by a treatment with metallic salts.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I would have it understood
that I make no claim to the process set forth in the Specification No. 7453 of 1890,
but what I claim is :-
The herein described process for the production of coloured pictures by
preparing a photographic layer with a diazo or tetrazo compound, exposing it
under a negative and afterwards developing the image by treating, with a diazo or
tetrazo compound, the decomposition product formed in the layer by the action
of light.
Dated this 25th day of February 1805
ABEL & IMRAY,
Agents for the Applicant.