Ceruleum
– common modern spelling- or coeruleum – old-style, from Latin cælum,
sky – or also " cerulean blue", "celestial" is a cobalt
stannate (tin
oxide SnO3 +
cobalt + H2O + ... – note that tin oxide gives a white
pigment,
PW15) or sometimes a cobalt chromite
(PB36)
in some manufacturers’ colour range (see opposite picture).
Since it contains cobalt, it is in any case extremely
costly.
Permanent, hiding, rather bright but subtle, broken, a
bit grayish, it constitutes oddly a "benchmark" for the warm blues -
recommended by some teachers and work books as a substitute to a primary
cyan (see
below) – whereas its composition and colour make it rather similar to an
intermediate blue – like its cousin, the
cobalt blue. It is cooler than manganese
blue (see
below).
The imitations (phtalocyanines),
very common because of the original’s high cost, are often rough, noticeably
warmer than the original. Moreover, the quite numerous versions of cobalt
ceruleum already offer quite a various range of undertones. This could
explain certain confusion.
Ceruleum is classified here among
warm blues for practical reasons, in order to facilitate the search for this
colour ; but actually it appears that its brightness must not lead us astray
and that it belongs rather to the intermediate, or even cool blues!
The use of the genuine ceruleum in oil painting poses
a problem: the cobalt contained is a very powerful siccative. Some authors
exclaim gleefully and naively that ceruleum is very siccative, as if it were
a benefit... On the
contrary, it is a
problem. Introducing in a painting a pigment with
such a power is not innocent: it induces notably the risk of causing
“siccativation differentials" which usually bring on puckering, cracks and
other unwanted deformations.
We recommend a very cautious and considered use of the
genuine ceruleum in oil painting for this reason except if it is applied
pure between two layers of insulating glazes (it is better then to use a
reasonable time of siccativation). Other processes certainly exist, but this
one is undoubtedly the most classical.
On the contrary, we recommend ceruleum without any
"technical" reserve for all other pictorial processes.
Whatever the painting technique, using ceruleum in blends - notably as a
substitute for a primary colour – is an aberration as much financial as
chromatic. Ceruleum is precious. The painter chooses it with attention. Its
colour is subtle. It lends itself to subtle rectifications with glazes or
tints or to pure coloration a lot more than to blends intended for learning.
The
manganese blue
Even more than for cobalt colours, its use in oil
painting poses a problem. It is an extremely powerful siccative (see notably
Courtrai brown). It is magnificent but
costs very much.
It gives rise to very interesting and very correct
copper-based imitations (see opposite picture).
Some violet pigments widely distributed contain
manganese phosphates ("mineral
violets") that we maybe have to mistrust
for a use with oil.
The Manganese blue and its remarkable imitation are
incredibly warm. They are "at the top of the blue", at the threshold of the
warm colours, unhoped-for. A dream in the world of pigments.
Read the article The Manganeses in The chemical families of
pigments.
Read the article Manganese in the glossary.
The "phtalo" blues
They are hydro carbonated and nitrogenous derivative
from
copper. Besides, their complete name is "copper
phtalocyanines ", which shows the presence of
nitrogen. Their genesis goes back to the beginning of the XXth
century. They are known with different appellations: blue
cyane, monastral or Helios blue (a title used for other colours,
emphasizing a certain light resistance).
They are very coloring but little hiding. They are
well adapted to
glazes (oil or other processes) and to
watercolor. They present most of the time good
permanence levels. André
Béguin highlights their remarkable heat resistance.
Coming in a variety of colours from green – copper
phtalocyanine added with
chlorine or
bromine, two
halogen elements
- to violet - copper phtalocyanine +
dioxazine -, they have enough chromatic
precision to make beautiful imitations (notably of the
blue known as "azural" , of the blue
"turquoise" and of the blue known as "Tuareg" or "Hoggar").
Besides, they have been used for a lot of nice
imitations, but also for some others that are clearly less successful.
Other copper
derivative
They have typically been realized by alteration of
verdigris. The first transformation processes of this type date from the
XVth century, or even previously. Others have existed, and the
list of copper pigments is long. We shall evoke only some of them.
The azure blue, azurite or
Germany azure
Not to be
confused with the homonymous colour (azure) which is cobalt based, and used
for stained glass windows (see
smalt).
Etymology :
see
glossary.
The azure blue,
azurite based (natural
copper carbonate, cf.
glossary article), is still used. It comes from a mineral.
This pigment is highly costly. It is a warm blue,
quite close to
manganese blue. When roughly ground, it would keep a brighter shade just
like the
lapis-lazuli and the
malachite.
Its first use in painting would date from the IIIrd
millennium BC, in Egypt.
During Roman antiquity, the first production area
appears to be Armenia. Azure is called lapis armenis then ("stone
from Armenia", existing also as a green variety, the
malachite) and is used in cosmetic. The next production areas are
Alexandria (maybe also Sinai) and, jointly,
Pozzuoli.
But the influence of azurite interests the whole
Eurasian continent.
In China, a pictorial use appears before the end of
the Antiquity whereas Western countries and Japan wait until the Middle-Age.
All over Asia, azure numbered among the important pigments, special enough
to raise commercial bonds until Europe (notably with Hungary).
The production areas changed as mineral deposits were
depleted.
Later, Germany became apparently a significant
production area, hence the terms "Germany azure", "Germany blue". Note that
the term blue ochre or, bit more often, blue ashes, are sometimes
used.
Today, Cyprus, France, Italy and again Armenia and
Germany would be the main extraction places for this mineral. In these
places as such, one often finds also
green malachite, which explains the double meaning of the term "stone of
Armenia".
During the Middle Age, Germany azure was bound , with
a "water gum" (gum
arabic) possibly added up with
egg white, casein
or
egg yolk, but not with oil (which appeared later). The grinding is light
(if too fine, would be duller, and this is not an isolated case). We don’t
have any knowledge about the behaviour of genuine azure in oil painting.
Blue ashes contain azurite and turn green upon contact with oil, but is
it because of this component? This is not to be excluded a priori,
but nothing allows us to claim it without
confirmation.
The
blue ashes and the Egyptian blue
According to our sources, blue ashes would be a blend
of
azurite and of mountain blue (a perfect
stranger: a priori we only know the
mountain green, but it is maybe a variant). Green ashes would be
produced as well – during the process of
silver refinement- on the same base: a copper
carbonate. Besides, blue ashes are noticeably known for turning green upon
contact with oil. It is then used with water-based paints (mostly with
gouache and watercolour), but even so, it could turn green (information not
confirmed).
This pigment would be produced mostly in the U.K. (the
fabrication process is kept secret). We believe that it contains oxided
copper and
lime carbonate in addition to copper carbonate.
It is a light and more or less warm blue. It is
supposed be fleeting or at the least versatile.
Current blue ashes are most of the time imitations.
The
Egyptian
blue
According to diverse sources, blue
ashes would be more permanent under its charred form: the Egyptian blue. In
reality, the latter cannot be reduced to simple
blue ashes
or a charred
azurite
: its original fabrication process, quite ancient (VIth century
BC according to some, at least 2500 even 3000 BC according to others) but
already very complex is little known. As soon as the IVth
millennium, the region was certainly in the middle of the chalcolithic
period but the knowledge of copper technology is not sufficient to explain
the ability to achieve
sintering
followed by grinding, the fabrication process usually
mentioned. Strictly speaking, we only know that we find in this blue: silica,
copper and
potassium
or
sodium
(they give subtle different hues). In addition, ancient Egypt is famous for
its precocity in the domain of
faience glazes and
porcelain glazes.
This composition, except copper,
reminds a little of the ultramarine, and therefore of the
lapis-lazuli.
This is maybe not fortuitous: some writers claim that the Egyptian blue was
an imitation of the precious gemstone. They base themselves on a translation
of the original Egyptian name.
If we stick to this, it might be
the first synthetic imitation in human history. A rough imitation yet, a lot
warmer chromatically than lapis-lazuli (because of the presence of copper).
We have to temper this point of view though: the distinction between the
different blue has been very vague for a long time.
But there is a doubt still. The
Egyptian blue looks particularly like
azurite
which it replaced for a major reason : copper carbonate
could not behave like a sintered substance (therefore "de-carbonated" when
baked, and silica-coated) whose
permanence
and
stability
are legendary.
By the way, it is worth noting
that the Egyptian blue has not been made only from azurite. Different
coppery components are mentioned. Even bronze has supposedly been used
(information not confirmed).
Rome imported this "Egyptian" blue
which has not been produced only in Egypt but in the whole area: Greece,
Gaul, Uzbekistan, Scandinavia, etc., are supposed to have imported this
colour before Rome did. Then, during Middle-Age, the recipe (or recipes) has
been lost like so many others. But nowadays, synthesises- very close as to
the chemical composition of the end products– are available and they have an
outstanding permanence.
The
celestial blue also called Bremen blue
Very different from the ceruleum blue in spite of a
similar nickname, it is a toxic derivative from copper arsenate discovered
during the XIXthcentury.
Other warm blues
The
Prussian blue, also called Berlin blue
Recommended reading :
the Prussian blue on Pourpre.com
Some authors mention Prussian blue as a substitute for
cyan
to be used in order to
learn colour synthesis in watercolour. A priori, it does not seem light
enough for that purpose (the opposite picture gives a standard
representation of its colour). It is very warm of course, but without any
addition of white (quite uncommon in this technique) it will never make a
good cyan; even if it is diluted a lot.
Likewise, this blue is interesting when blended, but
it is very cumbersome because of its huge (and apparently "repulsive")
coloring property, especially in oil painting or acrylic. For this reason,
it can be used first in small amounts in order to enrich a black or a grey
(about this, see
Payne grey).
Charred, it becomes a Prussian brown or a
Prussian black. Both are supposed to have a good permanence, but also
some inconsistencies. It is advised against practicing "home made -
calcinations" because from 250°C, this pigment starts decomposing partially
into elements that are poorly described by nomenclatures, but possibly
hazardous.
The Prussian blue is made of
iron cyanide complexes (ferric
potassium
ferrocyanide).
Strongly recommended reading :
The genesis of Prussian blue
in
Dialogs at Dotapea,
chap. X, the blue ochre
It has been discovered by accident in Berlin (hence
its initial name) en 1710 by Dippel – who is presented wrongly or rightly as
"questionable" - and Diesbach. Among other possible dishonest acts, Dippel
had supposedly sold to Diesbach the ironmonger some denatured potash
(possibly charged with iron) which would have caused Diesbach’s preparation
to turn blue.
In fact, there are several versions of the story of
this almost legendary discovery (cf.
Béguin, T. 1, p.155) and it
is very difficult to make a decision about the way it happened. An article
of the website Paint Café gives a version which is certainly
plausible but way too much affirmative according to us (link).
This story has ramifications: for instance the
creation of a "blue of Paris" or "blue of France", quite unsung because of
an odd transmission of knowledge mentioned by several authors. We can also
evoke the "blue Degottex", which could be - with reservations – a substance
of similar composition, obtained by reaction between red ochre and a
particular white earth.
An attribute specific to this pigment must be
mentioned: its washing takes a particularly long time and all the
productions do not have the same quality. According to André Béguin, some of
these pigments can show bronze-like glints while others, tending to the
green, are called "bronze-free" to mean a superior quality.
About toxicity,
we have to precise that Prussian blue does not break down
into "cyanide"
when ingested. It cannot be viewed as an actual toxic under common
conditions of use. On the other hand, we must point its dangerous
instability in the presence of strong acids, alkalis and lead chromate, not
to mention its decomposition temperature threshold which is not very high,
and already mentioned above (RepTox
information).
Recommended reading :
the Berlin blue on Pourpre.com
Behaviour
in painting
It is known as "siccative"
(a relatively suspect term) in oil painting, and that would not necessarily
be good news, as we said above, if this information were confirmed. But this
point appears to be questionable because iron is particularly jealous and
does not part easily from the surrounding oxygen atoms. Moreover, the
experience does not confirm clearly this assertion. On the other hand, it is
pleasantly absorbent.
Very light-stable except when blended with oil
(supposed to blacken – to be confirmed),
unstable
according to other
sources not necessarily well-informed, hardly permanent – supposed to become
transparent -, very colouring, it is actually suitable mostly for light and
local glazes and for watercolour. We must say, however, that some authors
recommend to wipe it off the palette in oil painting, and even in other
processes. We have to be careful with such radical blames, commonplace as
soon as some repellent terms like "cyanide" are mentioned.
According to some sources, Prussian blue collides with
Caparol ®. Information not
confirmed.
It would give "prussic" greens when combined with
yellows, colours that currently have a reputation of poor quality. One needs
to wonder about the exact composition of such
pigmentary compounds. It is the same for the "zinc
greens" containing Prussian blue.
Prussian blue has been used to make the charron blue.
See below
The charron or
charrette blue
Dotapea is looking
for information about this matter: we tested it and had very interesting
results. However, our knowledge of the composition and history of this
product is quite poor.
All we
can say is:
* It is
difficult to define its hue. Rather warm (see the opposite picture of a
trite pigment sold as "charron blue", probably copper
phtalocyanines) or rather cool (woad
version), charron blue is sometimes dark, sometimes light when enhanced with
white ;
* It is
made in France ;
* This
colour knew a traditional and probably very ancient use. The term "charron"
is a reference to the colour commonly used to paint the cart wheels (called
"charrons");
* Its
fabrication has been interrupted during a long time but has restarted;
* It is
used by some painters in different blends in order to create or enrich a
black, notably when combined with a red.
Its
composition is quite mysterious. The definition "Prussian blue charged
with
barium sulphate"
chosen by our fellow Yan Bilik of
Pourpre.com and different
sources (like
André Béguin, for whom "charron
blues are charged with
barite " - p. 156) does
not seem to correspond to the composition of some charron blues found in the
shops, which seem lacking of white. Above all, it is not impossible – with
reservation – that, originally, the craftsmen made themselves a blend of a
woad
–based pigment and
possibly (but we don’t know why) barium white or another white. The
traditional diversity of this blue could have been achieved from the
residues taken in the vats where the woad, European
" medieval or antique indigo",
was prepared.
Or wood could have been
dyed, like a
piece of fabric.
We had indirectly access to a testimony – not confirmed –
about a dye called "charron blue" in France, methylene blue - based, in
modern days.
Hypothesis : the charron blue would have been made initially from a woad
dye, which has been replaced by some more modern products later.
Something
remains especially disturbing about this colour whose name is associated
with the cart : it seems to remind the importance, noteworthy at the least,
of the cart in the ancient European traditions, notably by means of the
archeological treasure of Vix (chariot of Vix), while seeming to associate
to this colour a symbolic value, even more important, given in the Celtic or
Celto-Germanic antiquity to the blue colour, which was "taboo" for the
Romans and other Indo-European people. There is here a persistent mystery,
all the more interesting as the blue is nowadays again the object of an
obvious attachment.
To date,
many questions remain asked and any person having information about the
charron blue is heartily invited to contact us.
Click here
Read absolutely :
barjaweb.free.fr/SITE/Album/char.html
And also :
The charron blue on Pourpre.com
The turquoise
From this
stone is made a pigmentary powder, very costly because the grinding is
apparently not very easy to realize (no confirmed but plausible
information).
The
mineral deposits are in Iran and in New-Mexico (USA). Turquoise has been
maybe used as a pigment for fire arts during Egyptian antiquity ("Egyptian
paste"), but this information is not confirmed. On the contrary, we know
that a "turquoise colour" said "Egyptian blue" was produced by action of
soda
or sodium oxide on
copper.
Genuine
turquoise is quite little known of western authors in the field of the fine
arts, it is completely absent from the catalogues of the best suppliers, but
some painters use it. Nowadays, they buy it in Egypt notably.
The stone
is opaque. Its colour is not definite. It goes from a light blue to a plain
green. It contains copper in fact. This is a hydrated
copper aluminophosphate.
As we can see on the picture (thanks to
Catherine Lisack), it is
veined. It contains white, black and reddish
parts -->
It is impossible
to define exactly the turquoise colour !
Imitations
of this colour are quite commonplace on the market: these are, most of the
time, blue or green
phtalocyanines
which
colours are close indeed to the concerned minerals; but they cannot pretend
resembling the inimitable look of ground minerals.
IMPORTANT
: the finest grinding is not necessarily the most interesting for the
painter (read
about the lapis-lazuli in Cold blues or
above
the extract about azurite).
Recommended reading :
The blue turquoise on Pourpre.com
The cyan
It is a
synthesis that corresponds more or less to this
primary colour. It is
available in the "basic" or "study" charts of colour makers. And most of the
time it is copper
phtalocyanines.
Recommended reading :
The cyan on Pourpre.com
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