Oil Paint Additives

There is not a manufacturer I know that will disclose information about additives for the simple reason they view it as proprietary information. Natural Pigments and our brand of artists' oils, Rublev Colours, have eliminated this problem by not including any stabilizing or dispersing additives, hence there is nothing to disclose, except for the pigment and vehicle. We believe transparency and disclosure is an important issue to professional artists who are creating art works that they expect to have some degree of longevity. We readily disclose ingredients in our products to assist artists in their creative work.

I will list the most common additives used in the modern manufacture of artists' oils paints and medium:

Additive--Function

Aluminum stearate--Pigment dispersion and wetting, and pigment suspension

Magnesium stearate--Pigment dispersion and wetting, and pigment suspension

Hydrogenated castor oil--Rheological additive for thixotropic flow for pigment suspension

Organoclay--Pigment suspension

Bentonite clay--Pigment suspension

Calcium naphthenate or octoate--Pigment wetting and drier

Salt of polycarboxylic acid--Pigment wetting, dispersing and deflocculation

Modified urea--Rheological additive for thixotropic flow to prevent pigment settling


The above list is ordered according to usage (from most to least common) in the industry.

Notes

1. Stearates are usually added from 1 to 2% of the total weight of the pigment in the formulation. Some manufacturers add more while others add the least possible while still maintaining effectiveness.
2. Hydrogenated castor oil, which is a colorless wax when properly added to oil, offers benefits without some of the problems associated with wax. I would be surprised to know of any manufacturer today still using beeswax. Natural Pigments includes this additive (castor wax) in some of our painting mediums, but not in our oil colors.
3. Organoclay usually needs to be 'activated' by mixing it with a polar solvent, such as ethyl alcohol or acetone, and a small amount of water before adding it to the paint mix.
4. Bentonite clay is a naturally-derived mineral that typically requires a polar solvent and water to effectively function.
5. Calcium naphthenate or octoate is typically added with other driers, such as cobalt and zirconium, but can be used alone as a wetting additive.
6. Salts of polycarboxylic acid and modified urea are recently developed additives (within the last 40 years) and are less commonly used in artists' colors, because they are more effective with formulations of high functionality.

Absorbent Grounds for Oil Painting

In his Transactions (1806), S. Grandi describes a method of preparing an absorbent ground for panels, but for which he later wrote works equally well for stretched canvas. He described boiling sheep trotters* in water to remove the greasy parts, calcining them and then grinding them to a powder. Next, prepare a thin paste of wheat flour and add an equal amount, presumably by volume, of the powdered bone ash and grind the whole mass well together.

Apply the first coat of the bone paste to the canvas with a stiff brush, working it well into the weave of the canvas. Apply a second coat of the paste, allow to dry and smooth with sandpaper. A third coat must be applied, allowed to dry and lightly sanded smooth. Finally, apply a thin coat of linseed oil or walnut oil by rubbing it into the surface of the ground.

Pigments can be added to the third coat and a fourth coat of the paste, if a colored ground is desired.

Hundertpfund (1849) described the following method for preparing an absorbent ground:

Spread a thin layer of boiled flour and pipe clay over well-stretched, unbleached, even -threaded canvas. Let it dry and repeat the operation until the canvas shows no more open pores. If the paste is the consistency of liquid honey, the canvas will only require three or four coats. Afterwards, he recommends coating the ground with a thin lead white oil ground spread thinly over the entire canvas, and allowed to dry in the sun before painting.

The recipe for the flour paste is as follows:

Take a certain amount of wheat flour, mix it well with a little cold water in a pot, adding gradually more cold water and continually stirring until it appears like thick milk. Let it boil very slowly with constant stirring. As it thickens, stir it quicker, until it is a thick smooth paste, which must look shining. Now stir in some warm water, and let it boil slowly for half an hour. By continual slow boiling, it becomes smooth and smoother, so that it may afterwards be thinned with water, according to your liking. Now place some pipe clay in water until the clay is completely wetted, stir it afterwards with water to the same consistency as the flour paste, mix these two in equal quantities and pass them through a fine sieve.

When this mass is as thin as is required for watercolor painting, after it has been warmed again, spread it on the canvas or panel. If the first priming is laid on warm, it penetrates better into the support.

Bouvier's absorbent ground in his painting treatise called for the use of glue made from starch or 'belle farine' (flour); this was added to pipe clay** 'of the whitest and purest that can be procured from the chemist (marchand drogist).' The clay was mixed with the glue to the consistency of thick cream. The mixture was then rapidly applied with a large brush to an already sized support, the moisture being readily absorbed and the ground dried instantly.

The question of an even thickness, mentioned by Bouvier, seems to have been crucial. Doerner points out that a good chalk ground should appear uniformly thick when held up to the light, and should not show any gaps or crevices. Presumably, unevenness would leave the ground prone to cracking at points where the thickness varied. Bouvier stressed: "your ground should present you with a beautiful unified surface, without the colour being thicker in one place or another" after the recommended three or four coats of priming.

*Instead of sheep trotters bones, one may substitute bone ash that is already in a form that can be used immediately with the flour paste.

**Calcined kaolin is an excellent substitute for pipe clay.

Lead Sulfate

Origin and History
Lead sulfate (British spelling, sulphate), PbSO4, formed the basis of a number of white pigments that were made on a large scale in the 19th century and 20th century and sold under a variety of names, such as "Patent White Lead," "Non-poisonous White Lead," "Sublimed White Lead," etc. Some of these pigments did not consist entirely of lead sulfate but contained other minerals, such as zinc oxide, barite (barium sulfate), magnesia (magnesium carbonate), etc., in varying quantities. They were made by different methods and most of those sold were produced by patented processes. One of the first patents to show the use of lead sulfate as a pigment was given to William Cumberland of New York in 1838, U.S. patent number 767.

In the 19th century, three basic methods were used to prepare lead sulfate. The first method consisted of precipitating a soluble lead salt (lead acetate or lead nitrate in dilute solution; perhaps the best method is the one where lead acetate is used) with dilute sulfuric acid, the dilute acetic acid obtained in the supernatant liquid being used over again for dissolving metallic lead. A variation of this process was done by grinding litharge with one-fourth its own weight of common salt and treating the mixture with sulfuric acid. Lead sulfate was also obtained in large quantities as a by-product in the manufacture of aluminum acetate from lead acetate and aluminum sulfate.

The second method was obtained by roasting a mineral containing zinc sulfate and lead sulfide ore—lead oxide and lead sulfate being formed in the process—the product known as 'sublimed white lead' (Bartlett Lead). The fumes containing these products and zinc oxide were collected in chambers provided for the purpose. The product obtained in this manner was subjected to complex treatment. The composition of this product tended to be somewhat irregular; the shade was not always pure, being a bluish gray tint to white. 'Non-poisonous white lead' or patent white lead, and 'sublimed white lead' are mainly composed of lead sulfate with small amounts of lead and zinc oxides. The last-named is a basic lead sulfate with some zinc oxide.

Grinding precipitated lead sulfate with zinc oxide and perhaps other compounds under edge runners was a third method of obtaining lead sulfate. Freeman's White Lead was a mixture of lead sulfate, zinc oxide, magnesium carbonate and artificial barite (also called blanc fixe) obtained in this manner.

The naturally occurring mineral anglesite, PbSO4, occurs as an oxidation product of lead sulfide ore, galena. A number of lead sulfates are known: PbSO4·PbO; PbSO4·2PbO; PbSO4·3PbO; PbSO4·3PbO; PbSO4·4PbO; the first two are most commonly used in the paint industry along with a mixed pigment containing zinc oxide and barium sulfate.

Three methods of modern manufacture for lead sulfate pigments were used in the 20th century. The first was the formation of lead sulfate as a component of the mixture of zinc oxide and lead sulfate based on earlier methods made from ores through sublimation in controlled atmospheres. Second, in 1935, a new basic lead sulfate was made by precipitation that gave improved properties and higher basicity, but proved to be uneconomical and was abandoned after 1960. The third method, and one which produces most lead sulfate today, is formed by a fume process where molten lead is atomized in a jet flame in the presence of excess air and sulfur dioxide. Most of the lead sulfate today is used in manufacturing the active paste for lead acid batteries.

Lead sulfate pigments were sold under many trade names and it is not always clear whether they refer to the basic form. These include fast white, milk white and Mulhouse white for lead sulfate (Colour Index Pigment White 3), and basic sulfate white lead, Lewis white lead, sublimated white lead and white lead sulfate for basic lead sulfate (Colour Index Pigment White 2).

A lead carbonate sulfate mineral, leadhillite (PbSO4·2PbCO3·Pb(OH)2), was identified in pigments from the Tiantishan Grottoes, China. Lead sulfate pigments have been identified as artists pigments in 13th to 16th century Chinese paintings. It is also believed to have been used as a white pigment by late 18th century and early 19th century British watercolorists. George Field named lead sulfate "Flemish white" in his treatise Chromatography, while another form including zinc white and barite was sold under the name, "Freeman's white."

Permanence and Compatibility
Lead sulfate is a white, somewhat crystalline, very heavy powder; its specific gravity being about 6.3. It is only slightly soluble in water, insoluble in dilute acids and in alcohol, but soluble in solutions of ammonium salts and in strong sulfuric acid. Boiling concentrated hydrochloric acid dissolves it and crystals of lead chloride fall down as the solution cools. It is not readily acted upon by hydrogen sulfide, and is therefore, more permanent than lead white when exposed to air polluted with it. Owing to its solubility being less than basic lead carbonate, it was often sold as "nonpoisonous white lead."

Lead sulfate, according to Georg Zerr and Robert Rübencamp, is a color of 'dazzling whiteness.' Its color is a good white, but slightly yellower in tone than lead white and about equal to barite (baryte). The hiding power of lead sulfate pigment is less than lead white on account of its more crystalline nature, and its drying quality is also less. Lead sulfate is either a neutral pigment of crystalline structure with poor hiding power or a basic pigment with better opacity but less than basic lead carbonate. Compared to basic lead carbonate it does not mix as well with oil. According to Laurie, lead sulfate prepared by precipitating the lead salt with sulfuric acid had poor covering power but that produced by sublimation gave the best pigment. It was a pure white, slightly 'blue in color and covering as well as white lead.' Lead sulfate was less used alone than in mixtures with and shading other pigments.

Lead sulfate is unaffected by light. Lead sulfate is little affected by hydrogen sulfide found in air pollution. It was developed for use in outside house paints, because it did not have the same tendency to darken when exposed to pollution containing hydrogen sulfide. When applied in watercolor technique, however, traces of hydrogen sulfide in the air may cause it to darken. Although lead sulfate is theoretically incompatible with sulfide pigments, and should form black lead sulfide in contact with them, no examples are readily known.

Oil Absorption and Grinding
Basic lead sulfate absorbs a small quantity of oil, requiring 22 grams of linseed oil for 100 grams of pigment to form a paste. It grinds well with linseed oil, but not as easily as does lead white (basic lead carbonate).

Toxicity
Although writers in the 19th century often wrote that lead sulfate was non-toxic and hence gave the designation of 'non-poisonous white lead,' it is toxic if inhaled as a dust or if ingested. It is a cumulative poison, and repeated exposure may lead to anemia, kidney damage, eyesight damage or damage to the central nervous system (especially in children). Grinding and making the pigment into paint can be hazardous and the sale of lead compounds in some countries has been prohibited. Painters may suffer from "painters' colic" or "plumbism" if they are careless in using it. Care should always be used in handling the dry powder pigment so as not to inhale the dust. Do not smoke, eat or drink while using the pigment in any form, including in paint.


A Note About this Pigment from Natural Pigments
Rublev Colours Lead Sulfate is a bright white powder suitable for use in most media, but especially adapted for oil. It is tetrabasic lead sulfate made according to the modern fume process, resulting in a brilliant white powder of high purity.

Calcite--Types, History and Use in Oil Painting

Calcite is a naturally occurring calcium carbonate (CaO3) mineral chiefly found in rocks, such as chalk, limestone and marble. These rocks are the main sources for the pigment. Its whiteness, softness and fine-grained nature makes it an ideal white pigment, being both abundant and easily processed. Chalk is relatively transparent in most paint media and is therefore often used as an extender of other pigments and employed with animal glue as a ground for painting.

History of Calcite in Art
Calcium carbonate in various forms has a long history in art. It has been recognized, for example, in Greek and Roman art. Its use in art since that time has been both persistent and widespread. In northern Europe, from medieval times chalk was employed with animal glue for making the ground or preparation layer of paintings. Sometimes later lead white was mixed with the chalk to make it denser and whiter. Chalk was used with animal glue or with other aqueous binders as a white pigment.

Calcite has been used in oil painting, being added to colors, especially flake white, by such artists as Velázquez and Rembrandt. The transparency of chalk was desirable in some Dutch tonal landscapes of the seventeenth century.

Uses of Calcite in Paint
Calcium carbonate is commonly used in combination with other pigments in oil paint because of its low refractive index and hence poor hiding power. Linseed oil and chalk have long been used together, however, in the preparation of putty. The transparency of chalk in oil makes it ideal for adding bulk to oil colors or to affect the consistency (rheology) of paint.

Calcium carbonate is often used as an extender pigment to reduce the cost of paint. Its alternative names, such as chalk and whiting, are used in many formulations. An important use of calcium carbonate is in mixtures with titanium dioxide pigment to act as a spacer, keeping the titanium white particles spread apart, and ensuring better efficiency in scattering light and increasing opacity. Calcium carbonate is often used to vary the gloss of powder coating materials, depending on the particle size used.

Variations of Calcite and their Effects on Paint
Calcium carbonate derived from different mineral sources behave differently in paint. The material can be ground from limestone, a sedimentary rock formed in sea beads or alluvial deposits; or marble, which is limestone that has undergone heat and pressure below the earth's crust; or chalk, a light, low structure material normally associated with the sedimentary deposition of the shells of such minute marine organisms as foraminifera, coccoliths and rhabdoliths. The particle structure and chemical behavior of these variations of calcite all differ slightly.

The particle size and shape of calcite in regards to the behavior and performance of paint are important for several reasons. One is the viscosity of the paint, which is related to the volume occupied by the dispersed solids within the paint vehicle. In the case of particles that are not spherical, the “spherical equivalent” volume may be the maximum volume inscribed by the rotation of a particle. Because of this, a non-spherical particle may behave as if it occupies much more volume than it does.

Another consideration of the influence of particle size and shape on the behavior of paint is the surface area of the particle. The amount of paint binder required by a pigment to form a paste paint is called its oil absorption number. The greater the surface area of the particle, the more binder it demands to make into a paste or flowing paint. Synthetic (precipitated) calcium carbonate that consists of 0.05 micron needle-shaped particles has more surface area than the particles of ground limestone of the same size, which have simple structures resembling rhomboidal crystals. Because of the complex surface of the precipitated calcium carbonate, it will tend to scatter more light and consequently appear more opaque than the ground limestone particles. However, it is likely that this precipitated calcium carbonate will consume considerably more binder than the ground limestone.

Selecting the right type of calcite, taking into consideration particle size and shape, brightness, chemical constituents, and surface treatment are important factors when it comes to making paint or oil painting mediums.

Le Blon's Coloritto

Jacob Christopher Le Blon (1667-1741) was an engraver who developed what is perhaps the first system of color printing using three primary colors: red, yellow and blue. In his treatise, Coloritto, Or the Harmony of Colouring in Painting, he propounds a theory of painting that is of interest to students and professionals alike.

Le Blon describes white as a compound of the primitive impalpable colors, and black as a like compound of the palpable. True painting, he says, represents light by white, and shade by black, reflections by yellow, and turnings-off or roundings of objects by blue. Such is the outline of the brief and perspicuous theory of Le Blon, which, however deficient or defective, verges upon the truth and simplicity of nature.

Of Preliminaries.

Coloritto--or the Harmony of Colouring, is the Art of Mixing COLOURS, in order to represent naturally, in all Degrees of painted Light and Shade, the same FLESH, or the Colours of any other Object, that is represented in the true or pure Light.

Painting can represent all visible Objects, with three Colours, Yellow, Red, and Blue; sort all other Colours can be compos'd of these Three, which I call Primitive; for Example.

Yellow and Red make an Orange Colour.

Red and Blue make a Purple and Violet Colour.

Blue and Yellow make a Green Colour.

And a Mixture of these Three Original Colours makes a Black, and all other Colours whatsover; as I have demonstrated by my Invention of Printing Pictures and Figures with their natural Colours.

I am only speaking of Material Colours, or those used by Painters; for a Mixture of all the primitive impalpable Colours, that cannot be felt, will not produce Black, but the very Contrary, White; as the Great Sir Isaac NEWTON has demonstrated in his Opticks.

White, is a Concentrating, or an Excess of Lights.
Black, is a deep Hiding, or Privation of Lights.

But both are the Produce of all the Primitive Colours compounded or mixed together; the one by Impalpable Colours and the other by Material Colours.

True PAINTING represents
1. Light by White.
2. Shades by Black.
3. Reflexions by Yellow
4. Turnings by Blue.

N.B. In Nature, the general Reflex Colour is Yellow; but all the accidental Reflexions, caused by an opposite Body or Object, partake of the Colour of the opposite Body that caused them.

When a Painter says, that such Artists make a good Coloritto, he means, that they represent truly and naturally the Nude or the naked human Flesh; supposing they can paint all other visible Objects well, and without Difficulty.

In order to learn to paint a good Nude, or any other color'd Object, we must first learn to represent a white Object. For Example, To paint or represent a Head of Plaster, &c.

In which the White will serve to represent the Lights; and the Black the Shades; But White and Black are not alone sufficient like Nature is self, a white Object, which indeed represents a Print or a Design, but not a white Object.

To represent such a white Object, we must add to the Shades, or join with them the Reflex, or the Colour of the Reflex, viz. the Yellow; and with the Turnings off, or Roundings, we must join the Colour of the Turnings, viz. the Blue.

Only remember, that in natural Objects the Turnings off, or Roundings, are almost imperceptible.

To represent a colour'd Object, we may take an Head of Plaster stain'd with the Colour of Flesh, and set it in a good Light; and then we shall see that the same Colour of Flesh discovers it self throughout, or over all the Head, and distinctly enough, even in the Shades, in the Demishades or Mezzotints, in the Reflexions, in the Turnings off or Roundings, &c.

So begins Le Blon's theoretical discussion of color mixing in painting. In subsequent pages, he outlines a practical scheme of setting up the palette and individual color mixes for painting the various flesh tones in its shades and tints.

The basic palette of Le Blon consists of these pigments: 1. lead white, 2. vermilion, 3. red ocher, 4. brown ocher burnt, 5. lack (Indian or lac lake from lac dye), 6. umber, 7. burnt umber, and 8. black. Additional colors may be used are: Brown pink (or stil de grain), asphaltum, yellow ocher, massicot (lead-tin yellow), and "blew" (azurite, lazurite or indigo). This palette is almost identical to that prescribed by Roger de Piles some 40 years earlier.

The Palette of Michael Sweerts

It is no coincidence that the palette in the self-portrait by Michael Sweerts is practically identical to the palette described in detail by Roger de Piles in his 1684 book, Les Premiers Elémens de Peinture Pratique. Sweerts was a contemporary of de Piles, and it appears that his palette was laid out in the manner practiced throughout western Europe in the 17th century.

The pigments on the palette held by Sweerts in his self-portrait were analysed in detail in 1954 by Richard Buck and R. J. Gettens, and can be identified as: 1) vermilion, 2) red lake (possibly madder lake), 3) white lead, 4) yellow ochre, 5) red ochre or Venetian red, 6) terra verte, 7) a warm brown lake (stil de grain or brown pink?), 8) a cool brown pigment (unidentified, but likely a brown iron oxide earth pigment), 9) raw sienna, 10) Vandyke brown (or carbon black), and 11) an unidentified pigment that was lost.

Although we do not see the same arrangement of columns of shadow and half-tints prescribed by de Piles in his book, we do see mixes of vermilion and lead white like those written by de Piles.


Sweerts was baptized in Brussels on 29 September 1618. By the mid 1640s, he was living in Rome, where he remained until at least 1652. Back in Brussels, Sweerts opened an academy for life drawing in 1656, and became a member of the St. Luke's Guild in 1659. During a brief stay in Amsterdam in about 1660-61, he became a lay brother in the Lazarist Société des Missions Étrangères, and joined their mission to the Orient in late 1661. He was dismissed from the mission in 1662 because of his mental instability and ungoverned zeal, and died at the Portugese Jesuit colony at Goa in 1664.

In addition to portraits, Sweerts painted genre scenes and history paintings that combine stark chiaroscuro and blunt realism with a serene, almost classical simplicity.

Detail about the self-portrait: Michiel Sweerts (Flemish, Brussels 1618 - 1664 Goa [India]), Self-Portrait, ca. 1656, Oil on canvas, 37 1/4 x 28 7/8 in. (94.5 x 73.4 cm), Allen Memorial Art Museum, Oberlin College, Oberlin, Ohio.

Rubens' Palette, a view by Denman Ross

Denman Ross sets forth a 'set palette' in his book, On Drawing and Painting, Houghton Mifflin Company, 1912 that he says is based on the palette used by Rubens:

There is another palette, Palette 10, which should be mentioned which is not very far from being the palette which was used by Rubens and some other masters of the Renaissance. The form of this palette is shown on page 53. This palette, more than any other that I have proposed, reproduces the relation of colors and values which we see in the Spectrum. It was not, however, worked out with any particular reference to the Spectrum. It is based upon a color and value analysis of certain paintings by Rubens. In using this palette I am constantly reminded of Rubens in the way the tones come. I am reminded also of Correggio and of Turner. The descents from Yellow follow, as I have said, the value and color relations of the Spectrum, with an omission, however, of all violet tones. Violet rarely occurs in Renaissance painting. The lower tones of the palette are found in Burnt Sienna more or less mixed with a cool Green like Vert Emeraude. Below these orange and green tones comes a very dark brown, Van Dyck Brown or Cassel Earth, perhaps, which disappears in Black. The registers in Palette 10 are not repetitions of one another, but variations of the movement from Blue down to Red; variations which are so devised as to get the colors, as many as possible, to occur in the value of their highest intensities and in those intensities. Palette 10 is a palette for the lover of color.

On Drawing and Painting by Denman Waldo Ross:

This is not a palette based on historic equivalency to the pigments used by Rubens, but rather Rubens' palette using modern pigments in a modern viewpoint. Ross assigns RO to burnt Sienna, GB to chrome oxide (Verte Emeraude or chrome oxide dihydrate, Colour Index Pigment Green 18, 77289) and the other color notations with high intensity pigments as follows:

By Red I mean the only positive color which shows no element of Yellow or of Blue. It is the color which we often describe by the word Crimson. It is produced by the mixture of Rose Madder and Vermilion. By Yellow I mean the only positive color which shows no element either of Red or Blue. It is the color of the primrose, which may be produced by the pigment Aureolin with a very little Vert Emeraude. By Blue I mean the only positive color which shows no element either of Yellow or of Red. Blue is seen in a clear sky after rain and in the pigment Cobalt. By Orange I mean a positive color showing equal elements of Red and Yellow. By Green I mean a positive color showing equal elements of Yellow and of Blue. By Violet I mean a positive color showing equal elements of Blue and Red. (emphasis mine)

It would be interesting to attempt to reproduce Rubens' painting using this palette, as opposed to the actual pigments he used. However, it would be easier using a palette with his pigments and tints set in the manner described in de Piles' book.