 |
Home >>Brushes>>Paint Main Page
Yellow Pigments
Chrome Yellows.-This range of pigments is derived from the chromates of lead, barium, zinc, and strontium, and varies in colour from pale yellow to deep orange.
The lead chromes have great tinting strength and considerable opacity, and are moderately fast to light, though they tend to fade on prolonged exposure to sunlight.They can be safely mixed with the white basic and most other pigments, though not with those which, like ultramarine, contain sulphur. They are also affected by alkalis. Barium chrome, more usually known as" lemon yellow," is a very pale yellow, with properties similar to those of the lead chromes, though it has less opacity. It is used chiefly by artists.
Zinc chrome is also pale in colour, with a slight greenish tinge; it is proof against lime but is readily affected by acids and alkalis. Until recently, it found only a limited use in paint manufacture, but research carried out prior to and during the war proved it to possess valuable anticorrosive properties and it was extensively used for priming metal, particularly in the USA.
Strontium chrome is rather deeper in colour than barium chrome and has similar properties.
Ochres.-This range of pigments is prepared from natural earths, found in various parts of the world, notably in France, Italy, America, and Great Britain.
French ochres are the brightest in colour; they have considerable opacity and tinting power.
Italian ochres are slightly browner in colour and more transparent, as are those from America, which usually have a slightly reddish cast.
The finest English ochre is the well-known Oxford ochre, but the supply appears to be almost exhausted. Those found in Gloucestershire are more opaque than the Italian variety and have a brownish tinge, while those worked in Derbyshire are somewhat darker and redder in colour.
Ochres dry slowly, and are affected by acids, but are alkali-resisting and fast to light. They mix well in both oil and water.
Siennas.-Like the ochres, which they much resemble, the siennas are natural earth pigments, found principally in Italy. Raw sienna is of a dull, yellowish-brown colour. When roasted at a fairly moderate temperature, it becomes darker and redder, producing the pigment known as Burnt Sienna.
Sienna Will grind in oil and in water and will mix with white lead and other bases. Both raw and burnt sienna are affected by acids, though the burnt variety somewhat less than the raw.
Both resist alkalis and are fast to light.
They are used for staining purposes and play an important part in graining.
They are far less opaque than the ochres, but have better drying properties.
Aureolin.-This is a yellow pigment used, to a considerable extent, by artists and by decorators in fine work.
The tone is quite beautiful, being very bright.
The colour is also almost transparent and it is used for glazing. It is expensive, and therefore can only be used sparingly in decorative work.
Cadmium Yellow is a sulphide of the metal cadmium. If pure it is very permanent.
Cadmium yellow can be ground in any vehicle, and mixes easily with any other pigment except chrome yellow, emerald green, or other colouring matter containing lead or copper, which turns the pigment black.
It is sometimes adulterated with sulphur, which causes it to blacken on exposure to the air. Very pale tints are suspicious.
Cadmium yellow is expensive, and is only suitable for the finest of decorative work.