They
have been used mostly, sometimes as a base serving as a vehicle for colour -
like pastels-, and sometimes to lighten, shade the colours, or used pure to
draw in white (often on the body, and sometimes combined with fat
substances), sometimes as a simple base for the fabrication of a coating, or
still as a supply of calcium carbonate in the area of arts of fire.
Caution : they are not less toxic a priori than
other pigments even if they are natural.
The natural elements that are found in white earths
(calcareous
marls) are
* two
alkaline-earth metals:
calcium - major component
of
limes and
marbles, essential
principle of chalks and white earths in its carbonated form (see
calcite) - and, in varied
proportions,
barium, which can be
dangerous.
*
silicon, a
non-metal, and other
elements (see
Talc).
The
white that are the closest,
barium white,
lithopone,
silica, etc., are nowadays
the result of a chemical treatment from genuine natural marls.
All these
pigments (except silica white, in principle) may contain non-molecular
sulphur.
Pay
attention to incompatibilities.
Only a
part of the white earths is used in its natural condition and rather
massively in most of the regions of the modern world. In Europe, these are
*
Spanish white, used
during Renaissance for canvases priming, but also in decorative painting, to
make glazier's putty, and in the area of arts of fire. Actually,
the uses of Spanish white
are multiple.
*
Meudon, Toulouse or Champagne (Troyes)
white - see
Marls, oils and poisons
in Gesso - history and fabrication
and
picture above. The
quarry of Meudon is not exploited anymore today. It is now a listed place.
Recommended readings :
Meudon white on Pourpre.com
Historical informations on Meudon town website
Theses
whites are
calcareous
chalks. They are noticeably
alkaline and present
relatively similar compositions.
They are
clayey
(siliceous/aluminous) when their quality is low (hard).
They have
been used a lot for
distemper, blended with
casein,
lime,
gelatin, in interior or
exterior decoration. They are often grayish and generally have to be
associated to purer whites (lithopone, titanium, zinc).
Their
transparency, when they are combined with oil, would allow them to be used
massively as "transparent charge", as a thickener.
Our tests give different results, though,
just like the various testimonies we collected. In fact, a massive use gives
a very opaque, grey substance terribly lacking of "plasticity" : Reliefs
sprawl, blend and end up forming an indistinct impasto. This is because the
action of calcium, typical of some of its states. This alkaline earth metal
may react powerfully with an ester, like linseed oil (see
saponification). Using it
for light glazes could be perhaps a bit more interesting, but only the
fat-free paints (such as
distempers for instance)
will give lasting results with these pigments.
As we will see
below, we can consider that they have the
potential to remove oils.
A very peculiar use of Meudon white (or other white
earths) has been reported : see
Gros blanc
Finally, in the area of arts of fire,
barytes are used as a
supply of baryum,
calcites (chalks) as a
supply of calcium.
What distinguishes them from marble dust?
Their
chemical compositions are similar (calcite plus
some other elements). The difference lies
* in
their formation. Marble has been subjected to
metamorphic pressures.
Chalks would rather be alluvia (non confirmed information).
In any case they have not been subjected to such a
conversion causing a
crystallisation.
* in
their structure, because of this difference of formation. Notably,
marble is hard, waterproof
and
cristalloid whereas Meudon
white is only a very fragile
colloidal agglomerate of
small particles. Marble dust is principally a charge (link),
white earths are pigments. This statement will be moderated function of the
silica content and of the
structure of the concerned white earth (structure that will be more or less
crystalline).
See
Marble dust
How to remove oil from
a substance with a white earth
We shall
start with a testimony. This recipe has been given by a painter well-skilled
in faux marble finish.
To get rid of oils on a
glycerophtalic
paint, apply on top of it with a cloth or a sponge pure Meudon white,
without any binder. Let it
work
for one night then
wash.
Thus, the surface could be,
as we've been told, be painted with any water-based paint.
De facto,
we discover that in different decorative techniques, natural marls are used
to get rid of oils on different surfaces - oil-painted notably -, sometimes
combined with
methylated spirits, to make
the application of the pigment easier. We recommend a purer alcohol (ethanol
95%, high quality spirit for varnishing) so that the surface will not be too
adulterated by
denaturants. Alcohol
has the advantages of evaporating rather quickly and being less aggressive
towards fats than other substances.
Chemically, it consists in
saponifying a fat ester
with the help of an
alkaline substance. Thus we
obtain superficially separate matters (acids and alcohols) which have
difficulty to reconstitute as
fat.
To obtain deliberately a
layer that it will be easy to take off locally, in order to create some
effects, one sprinkles Meudon white on an oil-painted surface (dry), then
one applies directly water-based paint. It is a shock treatment for the
oil-based coat though.
These
processes evoke the fulling realized with
fuller's earth. Actually,
this earth seems used also in decorative painting to remove oil from
surfaces.
Kaolin
Kaolin, aluminum silicate
coming in the form of a soft rock, is used worldwide as pigmentary paste
(masks, make-up) for at least five hundred thousand years (source
Anne Varichon), but its use
in painting - including decorative painting - remains minority. In Europe,
it would have been used as a charge to reduce the covering power of some
pigments (see
coloured thickeners).
As a pigment, kaolin
is supposed to be worthless
with fat binders (oil,
egg, etc.), probably because of the drying
time during which it may show its tendency not to mix
with the binder and then... to fall ,
because the binder does not hold it (see
Pastes, charges and aggregates).
Maybe this tendency can be balanced with the use of
suitable additives, like waxes for example.
However,
kaolin is supposed to tend to make all the paints flake off. But, it is
renowned for giving good results with
casein and
gum arabic. With gum arabic,
it could bear a rather strong concentration (2/3 in relation to gummed
water, in volume, which is considerable). Information not
confirmed.
Seashells
white
Made from
powdered seashells (notably conch-shell), these pigments have been used as
they were in India, and later in China and in Japan or, in different places
of the planet - like ancient Egypt - in their calcinated form, like a lime
and used just like it, a fresco.
A use as
dye fixative is also found in China during the XIIth BC, whereas
the use of shells or seashells is proved in America and in Africa for body
painting.
Egg shell
is not exactly a white. This topic is treated in
coloured thickeners.
See also
The whites,
Distemper,
Fulling, fuller's earth.
We
recommend to read the fantastic book "Couleurs,
pigments et teintures dans les mains des peuples («
Colours, pigments and dyes in
peoples' hands »)", by Anne Varichon.
Umber white
According
to us this is certainly the most mysterious white. The subject is widely
treated in the chapter X of the Dialogs at Dotapea.
Click here.
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