FIELD OF THE INVENTION
The invention relates to a method for the formation of
a patina on a substrate, which is preferably manufactured from copper or copper
alloy. A patina formed of several layers is fabricated using the method. The invention
also relates to the corresponding multi-layered patina.
BACKGROUND OF THE INVENTION
Copper and copper alloys are coated with an oxide layer
in normal atmospheric conditions. Outdoors a brown oxide forms on the surface of
the copper and later a patina is formed at a varying rate, depending on where and
how the surface is exposed. The colour of the patina in urban and rural environments
is green and in marine environments mainly blue-green. Copper is recognised as a
long-lasting and maintenance-free material for roofs and facades. A natural patina
is a consequence of the corrosion of metal in the atmosphere. A patina layer has
a certain protective effect. The formation of a patina on the surface of a copper
substrate takes many years. It takes an especially long time in a clean rural environment,
where a patina may not be formed at all.
Several methods of artificial patination have been presented
earlier. When forming an artificial patina the copper surface to be patinated is
first treated oxidatively, so that a dark copper oxide layer forms on the surface.
US patent 3,152,927 refers to a method and paste, in which
method a patina gel is formed from basic copper nitrate and ferric sulphate. Basic
copper nitrate is not thermodynamically stable in rainwater, and instead changes
gradually into a stable basic copper sulphate. The colour of basic copper sulphate
and copper nitrate is blue-green, but iron sulphate is added to the patina and the
yellow colour compounds formed from iron during precipitation give the product its
WO application 03085169 describes a method for the fabrication
of patina pastes of different colours using stable metal compounds as colour pigments
in order to obtain the desired shade.
In addition to roofs and rainwater systems, patinated copper
is used nowadays more and more as a cladding material. As a facing material, a patinated
surface, either of the traditional green or of a different colour obtained by means
of metal compounds, is on the other hand quite uniform in colour. Surface designers,
however, have requested the possibility to get a more vibrant surface, in other
words to treat it with several different shades.
An attempt has been made to form a vibrant patina surface
by spraying patination material in droplets directly on top of a dark copper oxide
surface, so that the patina does not cover the entire surface. In this case there
is the danger that the amount of patina per square metre is too little, so that
over time it may dissolve away in rainwater, particularly on sloping surfaces.
PURPOSE OF THE INVENTION
The purpose of the method according to the invention is
to fabricate a multi-layered patina on top of a substrate material of copper or
copper alloy, covering the entire substrate.
SUMMARY OF THE INVENTION
The invention relates to a method for forming a multi-layered
patina on a substrate material, which is preferably made of copper or copper alloy.
The patina of the method is formed on the surface of the substrate material in at
least two different layers of corrosive copper-based patination material, where
the colour and/or composition of the layers vary from each other. According to the
method, the transfer of different patination materials onto the substrate is performed
on one processing line. It is preferable that at least the first patination layer
is made to cover the surface and the others are sprayed as droplets.
The invention also relates to a patina, which is formed
in at least two layers on top of a substrate material of copper or copper alloy
and so that the colour and/or composition of the copper-based patina layers differ
from each other.
The essential features of the invention will be made apparent
in the attached claims.
DETAILED DESCRIPTION OF THE INVENTION
When a patina surface is formed on top of a substrate material
of copper or copper alloy, the first layer on the substrate is usually a black-
or brown-toned copper oxide layer. In conventional patination, the patina of the
desired colour is sprayed as a uniform layer on top of the copper oxide layer. Now
in the method according to this invention, a patina is formed on top of the copper
oxide layer of at least two copper-based patination materials, which either differ
in colour from each other and/or they differ in composition. When patinating the
substrate, the spraying of the different patination materials is preferably done
on a single processing line, which consists of a separate spray and tank for each
patination material, from which each patination material is fed in turn.
One method to manufacture a vibrant patina is to form two
layers of patina of different colours on top of the copper oxide layer. The first
is a covering layer and the second is droplet sprayed on top of the first layer.
The first layer is for example black-toned and the second the traditional green.
The first layer may also be traditional green and the second layer for instance
Firstly, the first patination material is sprayed onto
the copper oxide surface of the substrate, in a quantity that is around 70 - 90%
of the total amount of patina. After this, a surface layer of the desired shade
is droplet-sprayed on top of the first layer. In this way a vibrant surface is obtained
and at the same time the thickness of the patina layer is still sufficient to withstand
the effect of rainwater.
A black-toned patina can be obtained for instance by oxidising
the patination material in the fabrication stage more than usual, so that the patination
material is at least partially oxidized into an oxide and turns black. It is sufficient
to form a black-toned patina when about 10-20% of the patination material is oxidized
into an oxide with the rest remaining normal patination material. Another method
to produce a black-toned patination material is to add a black pigment such as graphite
to an ordinary green-toned patination material. Grey patination material may also
be made by adding graphite to a green-toned patination material. As described in
the prior art, patination materials are produced from copper salts.
A method according to the invention has been described
above, in which the patina is formed of two layers and certain shades of colour.
However, it is clear that within the framework of the invention, other desired shades
may be chosen. As the need arises, a patina may also be formed by using several
patination materials of different shades. In the alternative described above, both
the first and second layers and any subsequent layers are stable, in other words
they will not change substantially over time. For example, brochantite or basic
copper sulphate, which is a preferred patination material for the surface layer,
is very stable. Brochantite is blue-green in colour, but usually iron is added to
it to achieve the traditional green colour.
Another method according to the invention to produce a
multi-layered vibrant patina is to form a patina on the surface of the substrate
(on top of the copper oxide layer), which is a reactive base layer and a stable
surface layer. A reactive base layer patination material is for example basic copper
nitrate, which over time turns into brochantite. A reactive base layer may also
be an unstable basic copper sulphate with various crystalline forms, which is essentially
blue in colour. The unstable crystalline forms of basic copper sulphate include
copper sulphate hydroxide hydrate [Cu4(SO4)(OH)6·H2O]
and posnjakite [Cu4SO4(OH)6*2H2O].
As a stable surface layer patination material, for example
brochantite may be used, which is very weather-resistant. Since the amount of sulphur
and sulphates in rainwater is so small nowadays, brochantite also acts partially
as a source of sulphate for the reactive layer patination material. When brochantite
acts as a source of sulphate small amounts of copper and sulphate are dissolved
from it into the rainwater, and are precipitated back as brochantite according to
the chemical balance. Pure brochantite is blue-green in colour, but iron is usually
added to it to give the patina its traditional green colour.
When some reactive patination material is used as the patina
base layer, one advantage of the reactive crystals formed using this method is that
the gradual change of the patination material into brochantite results in better
adhesion to the substrate than the direct manufacture of patination material as
brochantite. The base layer is sprayed on as a covering layer and the coverage of
the brochantite surface layer is around 80-100%, preferably between 80 - 95%.
The invention also relates to a patina that is fabricated
in at least two separate layers on top of a substrate made of copper or copper alloy
and so that the colour and/or composition of the copper-based patination materials
differ from each other.
The first layer of the patina according to the invention
is made a covering layer and the second and any further layers as droplike layers.
According to one embodiment of the invention, the patina
is formed from at least two layers, which are stable and different in shade. When
the first layer is formed to be black in tone, it may be done in at least two ways.
A black tone has been made by using a green-toned patination material, of which
some has oxidised into copper oxide. A black tone has also been made by adding a
black pigment such as graphite to the green-toned patination material. The patination
material of the second layer in this embodiment is preferably green in tone. When
the first layer is formed to be the traditional green shade, the second and any
subsequent layers have been made a different colour. When a grey shade is required
graphite has been added to a green-toned patination material.
According to another embodiment of the invention, the first
layer of patina is made reactive so that over time it becomes stable. The patination
material of the reactive layer is preferably basic copper nitrate or unstable basic
copper sulphate, which is at least on of the following: ramsbeckite [Cu,Zn15(SO4)4(OH)22·6H2O],
copper sulphate hydroxide hydrate [Cu4(SO4)(OH)6·H2O]
or posnjakite [Cu4SO4(OH)6*2H2O]. Unstable
basic copper sulphate is blue. The patination material of the second layer of patina
is preferably stable brochantite, of which the coverage is around 80-100%, preferably
Changes to copper sheets caused by weathering were studied
where the sheets had either a totally covering patina surface or where the patination
material had been sprayed as droplets on the copper oxide surface. The test was
carried out as a climate chamber test, which has been found to correlate well with
atmospheric testing. The length of the test was 250 h. It was found that the totally
covering patina surface withstood changes is the air well. On the other hand, in
the sheets where the copper oxide was partially exposed, the copper oxide reacted
and became reddish in parts.