Application: Rarely used in painting as a pigment on its own. Natural barytes has long been used by painters for purifying drying oils. The very fact that it loses its opacity and white color in highly refracting vehicles makes it suitable as an extender not only for white pigments but for a number of inexpensive students' and sketching colors as well. Blanc fixe has already been mentioned as ground for silver point [see also Lithopone]. It can be used in lime and silicate techniques.
Nomenclature: Barytes, permanent white, heavy spar, constant white, processed white, blanc fixe [for artificially precipitated products], barium sulfate [French: Blanc baryte; German: Permanentweiss, Blanc fixe].
Commercial Grades: (A) Pure qualities and those specially prepared for dispersibility are traded in seven grades according to whiteness [0 = whitest, 6 = darkest). (B) Is traded as a powder or as a paste in water. The powder is available in normal and fine grades. A third grade, used as a contrast medium in medical X-rays, is of no interest to painters. The pastes are mainly used in industry for photographic papers and similar purposes and need not be considered here.
Appearance: Ostwald found that barytes mixed in water only and brushed on smoothly reflects almost 100 percent of all incident light. It is thus the most brilliant white available. Unfortunately this property is considerably diminished by the effect of the unavoidable binding media, e.g., in oil it appears yellowish-gray. [Incidentally, magnesium oxide is now considered a better white standard for reflectance measurements.]
Permanence: Completely light-fast and inert to all practical purposes, hence the name permanent white.
Fastness in Media: May be used in all binding media but only in aqueous media do both (A) and (B) keep their white appearance.
Compatibility: Compatible with all pigments, therefore often used as extender.
Stability of Consistency: Moderate.
Tinting Strength: With all white pigments this is taken to mean reducing power. (A) is less than (B), but both are satisfactory in water-base techniques--in oil, very low.
Hiding Power: Satisfactory only in water-base techniques.
Transparency: Low in aqueous techniques; good in oil but of little practical use for painters.
Texture: (A) A surprisingly heavy powder with a certain ñtooth,î not always of highest purity, since the mineral may be colored pink by manganese and yellowish by traces of iron. The raw material is therefore usually purified. (B) A pure white powder, a little lighter than the natural product but almost as heavy as lead white.
Drying Effect: None.
Toxicity: Nonpoisonous if free from soluble barium salts and other toxic impurities.
Misciblity: As a powder very good, but settles out quickly in water-base systems. Attempts to obviate this troublesome characteristic with additives or by reducing particle size have so far not been successful.
Wetting: Good.
Oil Absorption: (A) Approximately eleven to fifteen percent oil. (B) Approximately twenty percent oil.
Group & Origin: (A) Natural mineral pigment; natural occurrences are mined and crushed. (B) Artificial mineral pigment made by precipitation from barium chloride and sulfuric acid.
Chemical Composition: Both (A) and (B) are barium sulfate [BaSo4].
Tests: Insoluble in acids and alkalis and completely odorless. This may serve as a primitive test to distinguish it from other white pigments. Natural barytes can only be distinguished microscopically from blanc fixe by a chemist specializing in such work.
History: (A) No exact information is available about the first use of natural barytes. It may be assumed that crushed, pure white, heavy spar has been used since very early times. (B) Blanc fixe was first introduced in 1830 by Kuhlmann of Lille [France]. It is assumed that a conspicuous reaction like the precipitation of barium sulfate may have been known to chemists before that date, but no historical records of an earlier observation have come to light.
Further Remarks: Although Barytes and blanc fixe are really only of indirect importance, artists should nevertheless be aware of their properties. Finally, a useful hint : blanc fixe, sufficiently bound with methyl cellulose to prevent chalking and applied to a smooth or even, fine-grained surface, makes an ideal and extremely cheap projection screen for color slides. [pp. 69-70]
The following is from: Church, Sir Arthur H., K.C.V.O., F.R.S., M.A., D.Sc., F.S.A., Sometime Professor of Chemistry in the Royal Academy of Arts in London. 4th Edition Revised and Enlarged. London: Seeley, Service & Co., Ltd., 1915. pp. 154-155.
Regarding:Baryta-White: Permanent white, Blanc Fixe, Permanent Weiss.
The mineral known as heavy spar, or barytes, has been used as a white paint, particularly as an adulterant for white lead. However finely it may be ground, it is always very inferior in body and covering-power to the artificially-prepared barium sulphate--the true blanc fixe. To make this, a cold solution of barium chloride of specific gravity 1.19 is prepared, and to it is gradually added in the cold, and until no further precipitate is formed, dilute sulphuric acid of 1.245 specific gravity. The barium sulphate is [p. 154] washed with cold water until the wash-waters are entirely free from acid; for many purposes to which the product is applicable [fresco and tempera painting] it should be kept under water.
Baryta-white is absolutely unalterable by an impure atmosphere, and is without action upon other pigments. It does not work well in oil, but a mixture of flake-white and baryta-white, in the proportion of 2 to 1, presents the advantage of being very much less affected by sulphuretted hydrogen than flake-white.
The artificial baryta-white may be distinguished from the natural by its much finer state of division, by its greater body, and by the purity of its whiteness. Baryta-white is not adulterated, but its almost absolute insolubility in hydrochloric or nitric acid enables it to be at once distinguished from zinc-white or white lead.
Several mixtures of barium sulphate and zinc sulphide have been introduced as pigments; they are not suitable for the palette of the artist. The reaction by which the majority of them are formed is brought about by mixing together solutions of two soluble salts, barium sulphide [BaS] and zinc sulphate [ZuSO4], when two new salts are precipitated, both insoluble, namely zinc sulphide [ZnS] and barium sulphate [BaSO4]. [pp. 154-155]
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