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Mars Yellow

Synonyms: Mars Yellow, Mars Orange, Artificial Ochre, Jaune de Mars

This pigment is a kind of yellow ochre prepared artificially. It may be made by precipitating a salt of iron mixed with alum by means of caustic soda, or potash, or lime. The salts of iron used are either green vitriol (ferrous sulphate) or the ferric chloride. If green vitriol be employed the precipitate formed gradually becomes yellow on exposure to the air. Upon the proportion of alum mixed with the iron salt depends the depth of the yellow colour in the product, for the alumina precipitated with the iron hydrate acts as a diluent of the colour. When lime is used as a precipitant for the iron compound (if this be green vitriol or ferric sulphate), calcium sulphate, that is, gypsum, comes down along with the ferric hydrate and basic ferric sulphate, and serves to lighten the colour.

By submitting the different varieties of Mars yellow to various degrees of heat, with or without a little nitre, a number of products of different hues are obtained, including Mars orange, Mars red, Mars brown, and Mars violet. All these preparations require very thorough washing to fit them for use on the palette of the artist.

The Mars colours are permanent when carefully prepared and thoroughly purified from soluble salts. They seem sometimes to have a slightly injurious effect upon a few of the best semi-permanent pigments of organic origin, such as the madder colours. This action may be due to the ferric hydrate in them combining with the colouring matter, and displacing some of the alumina previously united with it. In this direction it is probable that Mars yellow will be more active than the deeper-coloured pigments produced by calcining it at various temperatures.

Last Update: 2011-01-23