Method of Varnishing Metal in Light-resisting Colours by Means of Alizarine-colours.
Year: 1894

page_text: Date of Application, 11th Aug., 1894--Accepted, 15th Sept., 1894
Method of Varnishing Metal in Light-resisting Colours by Means of
Alizarine-colours.
We, JACQUES PERL and PAUL HERRMANN, both of 7, Scharnhorst Strasse,
of Berlin, in the Kingdom of Prussia, German Empire, Doctors of Chemistry, 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:-
A well known method for colouring metals consists in producing on the objects
to be coloured first a colourless coating by means of a solution of pyroxiline, and
in then dipping the articles into solutions of the respective colouring matters.
What is most important, however, for the industry in question is producing on
metal a gold-like colour of great resistibility against light. The method above
mentioned, as well as the older method of coating the respective objects with
coloured varnish by means of a brush do not yield light-resistible colours, the latter
turning soon pale when exposed to light.
The colours best resisting the influence of light are alizarine colours; these
could not be used hitherto for colouring varnish, as they are but very little
soluble and are, moreover, very liable to be discoloured by the resin-acid contained
within all resins. Also in the dipping-method above mentioned alizarine-colours
met with no success, probably as the requisite intensity of the colour could not
be attained.
If, however, the improved method hereinafter described is used, colourings of
high intensity and excellent resistibility against light may be attained.
The objects are dipped into a colourless pyroxiline varnish and are conveyed
to a drying kiln after the surplus of varnish bas dropped off. In said kiln the
objects are subjected to a temperature of 80° C. and are intensely dried, in that
the moist air is constantly removed, and dry air is constantly introduced into the
kiln. The layer of varnish is thus dried thoroughly, and not merely on the
surface, as had been the case in the methods employed up to now.
The dried objects after having become cold, are put into a solution of the
alizarine colour, or in a solution of alizarine and other colours combined respec-
tively, said solution being so strong that the articles need be dipped in only a
few seconds, in order to get the required intensity. A solution of said strength is
attained, for instance, by dissolving two portions of alizarine in one thousand
portions of an absolute alcohol.
After the respective piece of metal has been dipped into the liquid colour, which
operation, as stated, ought to last but a few seconds, the article is removed and at
once dipped into water.
There is caused by this process a conversion of the colour, in that the objects,
the colour of which has been up to then a light yellow, get instead of this colour
an intense high red-golden one. Said conversion is based on the circumstance, that
alcoholic solutions of alizarine colours are yellowish, whilst the colour of aqueous
solutions of said dyeing stuffs is a red-golden one.
In order to prevent the water from loosening the layer of varnish off the metal,
said layer is first of all intensely dried, as already mentioned; further, the
alcoholic solution of the alizarine colour ought to be as free of water as attainable ;
and, third, said solution ought to be of such a strength, that the objects need be
dipped in only a few seconds, as also already explained.

page_text: It is, finally, of importance, that the surplus of water adhering to the coloured
objects after being taken out of the washing water is removed as quick as possible,
which is performed best by shaking the articles vehemently.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
The method of varnishing, consisting in coating the articles with a colourless
varnish free of resin-acid, drying them thoroughly, immersing them into a solution
of an alizarine compound, without or with other colours combined respectively, in a
strong alcohol, and developing the colour by dipping the articles into water,
substantially and for the purpose as described.
ELS
י
By Robert Deissler,
JACQUES PERL,
PAUL HERRMANN,
38, Alexander Strasse, Berlin, C., Germany, Agent for the Applicants.