What is a pigment ?
It is a substance (pure pigment) or preparation (compound pigment) in the form of practically insoluble fine particles, unlike the dyes which are in liquid solution (dye for ink, for paint, for dyeing...).
Mineral pigments, organic pigments and metallic pigments can be found.
MINERAL PIGMENTS (oxides, hydroxides, metal salts)
They can be "natural", which is the case of ochers, earths, which are in the natural state, and undergo only a process of calcination and/or mixtures.
Or "synthetic" obtained by thermal and/or chemical reaction between several materials. We are talking here about "green chemistry". Their hues are less dull than that of natural mineral pigments.
Average characteristics of mineral pigments :
- Excellent resistance to light and weather ;
- High resistance to water, acids, alkalis ;
- Good coloring power ;
- High coverage ;
- Better resistance to chalking.
ORGANIC PIGMENTS (azo pigments, phthalocyanines, quinacridones)
Nowadays, organic pigments are essentially azo pigments (yellow, green, purple), phthalocyanines (blue, green) and quinacridones (red, purple).
They have a greater coloring power than mineral pigments, but are often more transparent.
Their behavior in the light is average.
METALLIC PIGMENTS (bronze, copper, silver, gold...)
The metallic pigments are metals or alloys in the form of powders, obtained by spraying or by chemical precipitation.
They are mainly used in creative leisure.
PIGMENT PURE OR COMPOUND PIGMENT
A "pure" pigment consists of a single chemical compound (yellow ocher, red ocher, its natural). A compound pigment is a pigment obtained by combining several "pure" pigments, natural or synthetic.
PIGMENTS UNDER CONTROLLED NAMES
It does not exist, for the names of colors used by the manufacturers, a rigorous control of origin of the name. For example, under the name "Earth of Siena", one can find : a natural ground extracted near Siena, simply ground and sieved, a natural earth of another origin having a tone and a similar chemical composition or a mixture of different natural materials.
We can also find a cinnabar, which is normally a sulphide of mercury, made from a combination of synthetic pigments whose tone is close to the real cinnabar.
That's why it's important to refer to the references in the Color Index, which lists thousands of pigments, dyes and fillers. These references include letters and numbers :
First letter : P for pigment
A second letter (and third letter for some) :
W White (blanc)
Bk Black (noir)
R Red (rouge)
Y Yellow (jaune)
B Blue (bleu)
O Orange (orange)
G Green (vert)
Br Brown (brun)
A number from 1 to 3 digits corresponding to the category of the pigment.
How to use them?
The pigments are used for coloring concrete, mortar, plaster, stucco, whitewash, paint, varnish, wax, casein, oil. In creative leisure, in binders such as linseed oil, gum arabic, acrylic binder, medium to paint, eggs, as well as in the ceramic industry.
Mineral pigments, natural or synthetic, generally resist external use (facade, fence walls, terrace). They can of course be used indoors (wall decoration, furniture renovation).
Organic pigments, on the other hand, are more particularly used in interior decoration and creative hobbies.
The totality of the pigments can be mixed together to obtain an infinity of hues.
It is important to supply the total quantity of pigment required at the site at one time and in the same batch. Indeed, there may be a slight variation in hue between two pigment productions.
Of all the elements constituting the concrete, plaster or whitewash, only the binder can be colored. The pigment is thus always dosed according to the weight of the binder.
COLORING FOR WALL DECORATION AND BUILDING
· Concrete coloring :
The binder in concrete is cement. The recommended dosages of pigments are from 3% to 6% of the weight of cement.
The use of white cement will give hues more vivid than in gray cement.
In order to avoid color variations from one mixture to another, keep the same aggregates, the same grain size and the same amount of water.
Smoothing on the surface, ruler or trowel, can also cause the rise of fine pigment particles and cause variations in hue.
· Staining of coatings and whitewashes :
When making coatings and whitewashes, some pigments (oxides and some mixtures) may leave more bright color marks (flares). To reduce this risk, it is recommended to prepare a pigment paste. To achieve this pigment paste, it is necessary to mix all or the pigments with a part of the mixing water and a few drops of wetting agent. The more this paste is worked before mixing it with the rest of the preparation, the more the risk of rockets will be reduced.
It is recommended to always carry out a test before application on a large surface.
The binder will be here, lime, cement or lime-cement mixture. The recommended dosages of mineral pigments are 10 to 15% by weight of lime or cement and for organic pigments from 3 to 5% by weight of lime or cement. Adjuvants will sometimes be necessary.
Choose a quality pigment
STABILITY IN THE LIGHT
It is the property of maintaining the intensity of the coloration after prolonged exposures to light. Natural mineral pigments have the best UV stability.
COLORING POWER
It is the ability of a pigment to communicate its own color to a medium or a pigment mixture. Some organic pigments color twice as much as mineral pigments.
COVERING POWER
The hiding power (or opacifying power) of a pigment in a binder and for a given concentration is measured by its ability to cover the surface of a support with two contrasting areas: black and white.
We will speak of "opaque pigments" or "transparent pigments", but the fineness of the grinding also has a great influence on the covering power, as well as the pigment / binder dosage. Transparent pigments will be interesting for oil glazes. Organic pigments are rather transparent whereas mineral pigments are generally more opaque.
SICCATIVE POWER
It is the ability of a pigment to accelerate the drying of the oil used as a binder. This criterion is important especially in the choice of grinding oils and mediums. A pigment may contain mineral compounds with a drying action, while some pigments may delay drying.
The list established with respect to linseed oil is as follows :
- Among the very drying pigments : manganese pigments ;
- Among the siccative pigments : red, yellow or black iron oxides ;
- Among the low drying pigments : ultramarine pigments, green earths ;
- Among the pigments retarding drying : calcination black.
DENSITY
TOXICITY
The Ocres de France's company has selected a range of pigments that is safe for humans and the environment.
However, pulverulent materials alone constitute a danger simply because of the fineness of the particles that can be easily inhaled. We recommend wearing a mask when handling pigments and keep them out of the reach of children.