Most black pigments are composed of some form of carbon, and the names used for carbon blacks produced by different processes are often very confusing and at times misleading. The blacks produced by carbonising vegetable materials are referred to by some authorities as ‘carbon blacks’ while others use the same term to include ‘gas black’. The term ‘vegetable black’ can refer to a ‘soot’ or ‘smudge black’, but it was also used for the finest grade of ‘lamp black’. ‘Coal’ and ‘small coal’ could once refer either to fossil coal obtained from mines or open cast workings, or to charcoal. ‘Drop black’, seems to have originally referred to the form in which the pigment was marketed rather than the pigment itself, and as a result the term has been used to describe ivory black, bone black, and vine black. The name is still sometimes used, but which black is referred to seems to differ from writer to writer.
Because carbon is opaque, no refractive index can be observed unless another material forms part of the pigment.
Please find below details for Charcoal, Coal, Galena, Graphite, Ivory and Bone black, Pyrolusite, Smoke blacks, Stibnite and Umber.
Charcoal
Other names include: blue black, vine black, Frankfort black, rebenschwartz, noir de vigne etc.
There is no refractive index as carbon is opaque.
When seen through the microscope by transmitted light, charcoal appears as brown and black particles as well as fragments which shade between the two colours. Many of the particles have an elongated form and a splintery outline. In some particles cell structures may be seen; in particular the pits may appear as circular or elliptical holes, sometimes regularly arranged and occasionally with their borders clearly visible. Often the particles will have broken along a line of weakness caused by a row of pits, and the the edge of the particle is marked by a series of semi-circular ‘bites’. The remains of rays or spirals may also be seen as dark parallel lines if they cross translucent brown particles. The remains of these and other cell structures can usually be seen more easily if the preparation is viewed by dark field incident light before a cover slip is applied, but some advantage may still be found if incident light is used once the cover slip is in place. The particles remain dark between crossed polars. Identifiable cell structures are only likely to be found in blacks made from carbonised wood.
Charcoal blacks are made by heating wood, or other plant material, with a very restricted air supply. Vine prunings and wine lees are carbonised in closed chambers after which the light black powder is washed to remove the potash. Charcoal, and in particular sketching charcoal, can be prepared in the traditional hemispherical pile which is made by charcoal burners, though most charcoal is now burnt in metal containers. Any even-grained wood may be used; beech is often mentioned but willow is traditionally used to make the charcoal for sketching. Peach stones (peach or almond black), and cork (Spanish black) have been used to make charcoal black in Europe; the coconut was used in India.
Sticks of charcoal have been used for sketching by artists of all periods, and traces of their work may be found on the ground layer of paintings. Charcoal was also ground and used as a pigment. Tingry mentions beech and says that it produces a bluish tone; he goes on to discuss charcoal made in small quantities from the clippings of vine shoots. This was ground on a slab of porphyry, and he points out that when coarsely ground it is a poor grey colour, but that the finer it is ground the better the black becomes. ‘Frankfort’ or ‘drop’ black seems to have been made from a variety of materials including vine shoots. Printing ink made from it is not as opaque as that made from lamp black but, although ink made from charcoal is unsuitable for wood block and letterpress printing, it is highly thought of by the makers of intaglio prints where the layer of ink is thicker. Charcoal was sometimes incorporated in grounds. The Dictionary of Arts and Sciences of 1754 says that after the first layer has been smoothed with pumice, a second ‘couch is sometimes applied composed of white-lead and a little charcoal black, to render the ground an ash-colour’. Charcoal has been found by the authors in a chalk gesso ground on an eighteenth-century French harpsichord.
The Flemish painters valued charcoal black for the purity of the cool greys it gave when mixed with white. This quality seems to have been appreciated by Norgate as he recommended it for painting silver and pearls. Charcoal back was used both in oil and watercolour. The name ‘blue black’ appears in the middle of the seventeenth century, and seems to have been in use ever since. Vine black watercolours were still sold as ‘blue black’ at the end of the nineteenth century. It may seem surprising that other pigments would be substituted for something as cheap as charcoal, but Church claimed ‘that the beautiful bluish blacks, derived from such materials as the shoots of vine and beech, are frequently fraudulently imitated by mixtures of lamp-black and indigo’, while more recently at least one firm used the term to refer to an undefined carbon back in watercolour, and to a mixture of ivory black and ultramarine in oil.
Carbon blacks can normally be regarded as permanent, but if they retain tarry material, or if the carbonisation has not been sufficiently thorough they may become greyer with time. The carbon blacks are all poor dryers in oil, and will even impede the drying of mixtures in which they are incorporated; if used alone they produce very soft films. To counteract the slow drying it was recommended in the eighteenth century that verdigris should be added; Mayer suggests adding umber for the same reason, this would also have had the effect of toughening the film. He also points out that vine and other vegetable and animal carbon blacks are not suitable for use in fresco as they are liable to include water-soluble impurities and consequently effloresce. Church points out that charcoal and animal blacks have the ability to absorb the colouring principle from organic pigments.
Coal
Sometimes described as Mineral coal, to distinguish it from charcoal.
Thick particles appear opaque, but thin pieces or edges may appear to be greater or less than 1.66.
In plane polarised light, coal appears as brown and black irregular particles with sharp edges. Large particles tend to be opaque, but they can graduate in thickness and appear brown at the edges. Between crossed polars, the translucent particles and the edges of large ones, show an undulose extinction due to strain. This feature may not be observed in some ‘hard’ coals. With incident light, highly reflecting faces can be seen and some of these may show a conchoidal fracture. The refractive index varies and may be above or below Meltmount. Very occasionally, evidence of coal’s botanical origin may be found in the form of pits etc and such particles appear like anisotropic charcoal.
In the past coal was sometimes referred to as mineral coal, ground coal, pit coal, Scotch coal, sea coal etc. to differentiate it from charcoal, but prior to the early part of the eighteenth century the term ‘small coal’ could refer either to small fragments of mineral coal (also called ‘slack’), or to charcoal, and as both charcoal and mineral coal were used as pigments it is unsafe to assume one or other meaning unless the context makes it clear which is meant. Purchases of coal by painters are likely to have been for heating, but that mineral coal was used as a pigment is clear because Norgate comments that in contrast to vine black which was a blue black, ‘sea-coal’ makes a ‘red black’, he recommends that it should be ground finely in water, then dried and mixed with oil. John Smith in his Art of House Painting of 1676 mentions the use of sea coal. The authors found coal used in seventeenth century graining at Lambeth Palace. Several nineteenth-century books refer to the use of coal, but it is difficult to know to what extent coal was in normal use. Field mentions both sea coal, and a soft textured mineral which is found in Devon, and it seems likely that he was referring to finely fragmented coal that came from a seam near Bideford and which became known as ‘Bideford black’ at the end of the eighteenth century [Remington]. The last working Bideford-black mine closed in 1969. Bideford black is essentially a mixture of low grade coal and clay. Its staining power was low and some of its more recent uses included anti-fouling and anti-corrosive paints. Lower grades of mineral black were used in wood fillers. Eaton writing in 1929, says that slate and ground waste coal were used for cheap black paints, and that as they were seldom of sufficiently good colour by themselves other blacks, such as lamp black and ground charcoal, were added to them. It seems likely, therefore, that coal was used continuously, at least from the beginning of the seventeenth century, and possibly earlier, to the first half of the twentieth century, for cheap black paints.
Galena
Natural black lead sulphide. PbS; Cubic
Galena has perfect cubic cleavage and this means that when it is crushed, particles tend to show a ‘stepped’ profile which can often be seen under the microscope. If the slide is viewed between crossed polars with suitable centered bright field incident light, the particles will not show bright and extinguished positions, though the edges of the particles may appear bright.
N.B. This file has not been finalised.
This material occurs in a painting in the National Gallery London and which was probably painted in 1499. See: Marika Spring, Rachel Grout and Raymond White; ‘Black Earths’: A study of unusual Black and Dark Grey Pigments used by artists in the Sixteenth Century: National Gallery Technical Bulletin Vol 24 pp. 96-114)
Graphite
Plumbago, Black lead.
Carbon
In transmitted light, graphite appears as very irregular shaped particles. These are opaque, and at low magnifications appear black. However, when the preparation is viewed with a higher power dry objective, and a very bright light is used, enough light may be reflected onto the top of the particles from the cover slip for one to be able to just see the geometric shapes which are formed by crystal edges on the surface of the particle, but the surface of the particle needs to be focused very carefully. With incident light, these planes reflect brilliantly.
Graphite is a grey natural mineral with a greasy feel to it, which is found in several parts of the world including Germany and Madagascar. Its purity varies, from practically pure carbon to mixtures containing over half their weight in silica and alumina. Apart from when it was made into pencils, it was hardly used by artists. However, it forms excellent protective coatings because the particles tend to arrange themselves as overlapping plates. Such coatings are seldom used without additions, because if the graphite is pure the paint tends to spread, thus reducing the thickness of the coat. Quartz is therefore added to the graphite if the natural material does not contain sufficient silica. Under the name ‘black lead’ it was used on stoves and grates. Gilders added it to English clays to allow them to be burnished and during the early part of the nineteenth century it was used with prussian blue and clay to make ‘black bole’.
Ivory and bone black
Animal black, Paris black, Noir d’ivore, Elfenbeinschwarz
Calcined animal matter
In transmitted light the particles appear to vary in colour from grey to black; larger ones are often speckled. They tend to be rounded and the size can be up to about 7 micrometres but larger dull black aggregates coated with fine particles can occur in poorly dispersed samples. Particles of about 5 micrometres which are still white or grey are likely to be unburnt or semi-burnt material. Between crossed polars most of the particles will appear anisotropic provided that the illumination is sufficiently bright, and the light may well have to be turned up to see this. In one sample which was believed to have been made from pure ivory, the particles were smaller and more even in size than in other samples which the authors have examined, but it is not clear whether this is a characteristic of ivory or an indication of the greater care taken in the pigments preparation.
Ivory and bone blacks are prepared by boiling bones to remove the fat and gelatine, they are then ground and the harder (coarser) material calcined to make the black. At one time the preparation of bone black was associated with sugar refining and also with glue making. Commercial bone blacks vary in their composition. According to Mattiello [Vol 3 p 45] ivory black usually contains 10 – 20% carbon, and 80 – 90% calcium phosphate. About 6% calcium carbonate is often present as well. It is the presence of calcium phosphate that explains the birefringence which is seen, and which distinguishes this pigment from other carbon blacks.
A number of materials seem to have been used to make this pigment, they include stag horns (which are a type of bone), walrus ivory, elephant ivory and bullock bones. One seldom hears of bone black as most of it was sold under the name of ‘ivory black’. However, with the concern for wild elephants, this attitude to the name could well be changing. It is likely that some colourmen sold genuine ivory black as ivory turners sold their waste to be made into ivory black. Field says that, though ivory does produce the best pigment, the main difference between blacks of this type is in the preparation rather than in the materials. At their best ivory and bone black are fine, durable, neutral blacks, that may be used in oil or watercolour. If insufficiently burnt they are brown, and they dry badly, while if they have been over burnt, they are opaque and have poor colour.
Dossie says that ivory black was made in very large quantities from bones ‘for coarse uses, and [they] sell it at an extreme low price, it is therefore so grossly levigated, being ground only in hand or horse-mills, and so adulterated moreover with charcoal-dust, which renders it of a blue cast, that it is wholly exploded from all delicate purposes, and lamp black used in the place of it …’. He also recommends its use in water and varnish and adds in the section on japanning that ‘Black grounds may be formed by either ivory-black or lamp-black: but the former is preferable …’.
In the field of commercial paint manufacture, J. Cruickshank Smith writing in 1924 says: ‘buyers of paint will seldom pay the price for an unadulterated black …’ [made of bone black with a proportion of carbon black and a trace of prussian blue], and ‘… cheapening agents have to be introduced. Of these, barytes and whiting, in the proportion of two parts of the former to one of the latter, are likely to be selected …’. The manufacture of Paint third edition, p182.
Pyrolusite
A natural black soft earthy manganese dioxide mineral.MnO2 Tetragonal
In plane polarised light, our one sample was opaque and broke into long splintery particles. The mineral has perfect cleavage and a rough fracture. If the preparation was viewed with crossed polars and suitably centered bright field incident illumination, most of the particles showed bright positions and brief dark ones, which occured when the long edges of the particles were in line with the polars, due to double reflection.
This pigment has been recorded in eleven Italian paintings nine of which were painted about the middle of the sixteenth century. The remaining two were probably painted during the first half of the seventeenth century. It has also been recorded from paintings by Cuyp and Verspronck. It was used much earlier and appears in the cave paintings at Lascaux, on wall paintings in Cyprus and on Greek paintings of the bronze age.(See: Marika Spring, Rachel Grout and Raymond White; ‘Black Earths’: A study of unusual Black and Dark Grey Pigments used by artists in the Sixteenth Century: National Gallery Technical Bulletin Vol 24, pp. 96-114)
It is unusual to find crystals, Typically the mineral occurs as an earthy powder or as fibrous aggregates.
N.B. This file has not been finalised.
Smoke blacks
Lamp black, gas black, channel black, vegetable black, flame black, furnace black, etc.
Note: these blacks are opaque and can be amorphous or crystalline.
The individual particles of lamp black are too small to be resolved by the light microscope, so any particles that are seen are aggregates. The dry pigment tends to form large and complex aggregates in dispersions and often appears as rather angular chains, which are likely to interlock to produce an open textured black mass. Once the dry pigment has been made into paint, it never looks like this. Even small aggregates are opaque and so there is no refractive index. When a dispersion is made from an oil- or varnish-bound paint film, it seems to be impossible to break the pigment down into its component units, and the aggregates that are seen are likely to appear as solid dull black angular particles or thin grey smears. N.B. This means that if one makes up a slide from a bottle of dry lamp black, the particles will not appear similar in form to those on a slide made up by dispersing a lamp-black paint layer with a solvent.
Lamp black is really smoke and in its simplest form, is prepared by burning resinous or oily materials with a restricted supply of air, beneath a funnel where the carbon is deposited. In a more commercial method, the smoke was led through a series of chambers where it was deposited on the walls. The black was collected by men wearing respirators who swept the walls of the chambers down with soft brooms. The black which is deposited first tends to be brownish in tone and to contain a higher proportion of tarry material. The finest particles are carried furthest and are deposited in the last chambers. This black was bluer and was often sold, rather surprisingly, as ‘vegetable black’. More recently natural gas from oil wells has been burnt in jets beneath a moving metal channel or a revolving cylinder, the black is then scraped off into containers. This black was known a ‘gas’ or ‘channel’ black. These blacks contain less tarry material, wet out more easily, but are browner than the best grades of lamp black. In commercial paint manufacture, adulteration of lamp black is described as frequent by Cruickshank Smith, ‘black oxide of iron and cheap mineral black being both found …’. This point was confirmed to the authors by Panu Kaila who said that lamp black used to be adulterated with coal in Finland.
If the black is not perfectly made it will still contain unburnt tarry matter and will need to be calcined. This was well understood by printers in the eighteenth century, and some of the best blacks used in printing inks were calcined several times. ‘Furnace black’ is prepared by a method developed in the present century. Air and hydrocarbons are fed into a furnace, part of the hydrocarbon is used to maintain the furnace at the correct temperature, while the reminder is converted into carbon. These blacks tend to be coarse in texture and are little used in paints.
Smoke blacks have been used since prehistoric times. They can be regarded as permanent in all mediums. Apart from their use in fine art, they have been used in protective coatings and in the non-stoved variety of black japan on wood and papier maché foundations. Although they have been used extensively on iron work, there is some doubt about the soundness of this practice. Cruikshank Smith also suggests that on wood work, a grey paint made with lead white and smoke black lasted better than either pigment used alone. Smoke blacks have a high oil absorption, and paints made entirely of these two components are bad dryers. If the pigment has not been carefully prepared it does not wet out easily with water because of the residual oily material present. Gas blacks are reputed to be better in this respect than true lamp blacks. Smoke blacks have great covering power and are strongly staining, but they tend to make mixtures in which they are incorporated heavy in tone. Smoke blacks are sometimes sold in pellets of compressed pigment. While this makes the pigment less bulky and easier to handle, it also makes it more difficult to disperse in any medium.
Stibnite
Natural Antimony trisulphide. Sb2S3 orthorhombic
This mineral has a metallic lustre and is remarkably transparent to infrared light.
Under plane polarised light a preparation made from our single compact sample showed particles that included steps rather like pyrolusite but the steps were less square and often included a curved side. The material is supposed to be transparent to red light as well as infrared, but our attempts to make the particles appear red with the help of a Chelsea filter failed. When the preparation was viewed between crossed polars with suitably centered incident bright field illumination, a number of the particles changed from bright to dark on rotating the stage, due to the double reflection of the mineral.
Stibnite typically occurs as narrow prismatic crystals with longitudinal striations, aggregates are usually rod- or needle-like, although they may be granular or compact.
Stibnite is an important ore of antimony. Antimony was used in bell foundry, to prepare a yellow colour to paint on pottery and glass, and as a constituent in type metal. Powdered stibnite was used by the Greeks and Romans as a cosmetic to darken the eyelids. As a black pigment, stibnite has been found on gothic and much later sculpture. It has also been found in a number of North Italian paintings of the early decades of the sixteenth century. Stibnite appears as a dark grey when used alone, and as a clean lighter one when mixed with lead white. See: Marika Spring, Rachel Grout and Raymond White; ‘Black Earths’: A study of unusual Black and Dark Grey Pigments used by artists in the Sixteenth Century: National Gallery Technical Bulletin Vol 24 pp. 96-114)
N.B. This file has not been finalised.
Umber; raw and burnt
Raw umber, burnt umber, Cyprus umber, Levant umber, Turkey umber etc. Terre d’Ombre, Umbra natur, Umbra gebrannt.
An earth pigment containing hydrated iron oxide and 8-20% of manganese dioxide, often with a small amount of silica, alumina, organic matter etc.
Refractive index, raw 1.87 – 2.17: burnt 2.2 – 2.3
Under the microscope it can be seen that raw umber is composed mainly of rounded particles that range in colour from a dull greenish yellow to black, but with some warmer orange particles and a few that are reddish. The particles vary in size from 1 – 10 micrometres. Small rods may be present, and the pigment often appears rather like a slightly greenish yellow ochre. Between crossed polars, the birefringence of the pigment is low, but samples may include quartz and other birefringent particles. Burnt umber appears similar as far as particle shape and size is concerned., but though some small greenish-yellow particles are likely to be present, most are red or orange so that the impression is of predominantly warm coloured particles. McCrone says that burnt umber is isotropic, however a number of the particles in examples examined by the writers did not remain entirely dark when rotated between crossed polars.
The pigment is prepared by dry grinding, followed by levigation and drying. The best grades then appear as a voluminous brown pigment. Raw umber is found in many parts of the world, probably the best known is ‘Turkey umber’ which may have originally come from Cyprus through Constantinople, but by the early part of the twentieth century the name was applied to umbers that came from various parts of Southern Europe, Umber is, or was, also mined in Germany, the U.S.A. and England; J. Cruickshank Smith mentions that it was mined at Ashburton in Devon until the quarries became worked out during the 1920s. Burnt umber is prepared by calcining raw umber at dull red heat. The colour is a warm brown and the pigment is more transparent than raw umber, but otherwise has the same properties as the unheated earth.
Raw umber is a cool toned brown which is particularly valuable in modifying other colours. As a natural material it has been available from the earliest times, but according to Thompson, it was not used in European paintings before the end of the fifteenth century. It was used by painters during the seventeenth century but Dossie says that although it had been much used previously, it was little used by oil painters at the time he was writing. He goes on to say that due to its drying power it was ‘much used in the making [of] drying oils, the japanners gold size, and the black oil lacquer’. Both raw and burnt umber were used extensively in graining, and Nathaniel Whittock mentions that they are ‘very useful in distemper’. The pigment is reliable in all mediums and is not subject to fade if exposed to light. The oil absorption is high and it has the curious feature that, though it acts as a dryer, when added in small amounts to other pigments in oil, drying may be delayed if it forms a large proportion of the mixture[OCCA].
Mactaggart, P. & Mactaggart, A. (June 2007) ‘Black and Brown Pigments’ In: Pigment ID using Polarised Light Microscopy from: https://academicprojects.co.uk/black-and-brown-pigments/
