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Fortress of Louisbourg National Historic Site of Canada
Recherche sur la Forteresse-de-Louisbourg Lieu historique national du Canada
CENTURY PAINT MATERIALS
AND THE PAINTERS CRAFT AS PRACTICED IN LOUISBOURG
Report H G 05)
Paint materials imported or produced in eighteenth century Louisbourg. (See Appendix I) - of what they were made, and a bit on how they were made.
In very general terms, paint can be defined as a suspension of solid pigment particles in a liquid vehicle.
The vehicle usually consisted of a binding medium and a thinner. When the mixture of pigment, binder and thinner was brushed onto a surface, the thinner evaporated leaving the binder behind to form a solid film that held the pigment fixed in place.
A pigment is an insoluble substance that is mixed with a vehicle to make a paint. Besides lending color to a finish film, pigments serve three major purposes: they thicken the fluid film so that it can be applied in heavier layers; they help make the dried vehicle less porous; and they lend hardness to the paint.
Pigments were derived from both organic and inorganic sources, or in other words, they were procured from the animal, vegetable, and mineral kingdoms.
Many of the mineral pigments, such as the ochres, were mined directly from the ground and required very little processing before being incorporated into paints. In other instances, pigments had to be synthesized from available reagents, that is, producing pigments by uniting chemical compounds, or by degrading a complex compound.
A number of pigments commonly available in the eighteenth century were manufactured by methods that called for a relatively sophisticated knowledge of chemical science. Subliming vermilion, or precipitating Prussian blue, for example, were rather skillful tasks. Separating a pigment from solution or suspension by heating causing the element to pass from solid to the vapour state and condense again to a refined solid form required elaborate apparatus and fairly precise control of chemical reactions. Generally speaking, most of the pigments used in eighteenth-century North America were imported by the colonists.
RED OCHRE: a red pigment composed of a mixture of iron oxide, clay and silica. It was in great demand as a pigment since it was quite inexpensive, of a bright color, and did not fade. Red ochre was mined directly from the earth, or it could be made by calcining yellow ochre, that is, by heating to a high temperature in order to effect a useful change in oxidation. Much of the red ochre used during the eighteenth century was probably made from yellow ochre rather than dug up as red ochre.  Many painters probably burned or calcined their own pigments rather than buying it already processed because they could then be sure the ochre was pure and could also make it as "light or as dark" as they desired, depending on how long they kept it exposed to the heat. This was done by placing the yellow ochre into an iron ladle, or a crucible, and set over a clear fire where it remained until the desired color change was effected.
YELLOW OCHRE: a yellow pigment composed of clay and hydrated ferric oxide. Although the pigment was somewhat dull, its "cheapness and durability" caused it to be widely used. After the ochre was dug from the earth, it had only to be washed, levitated, and dried before it was fit for use. The process, called washing and levitating worked particularly well with pigments such as ochres and chalks which had a "coarse and sandy nature,"and which were extremely difficult to grind. The technique was quite simple and required little more than a few small tubs or buckets and a supply of water:
Take what quantity of the color you please to wash, and put it into a vessel of fair water, and stir it about till the water be all colored therewith; then, if any filth swim on the top of the water, scum it clean off, and when you think the grossest of the color is settled to the bottom, then pour off that water into a second earthen vessel that is large enough to contain the first vessel full of water four or five times; then pour more water into the first vessel, and stir the color that remains, till the water be thick; and after it is a little settled, pour that water also into the second vessel, and fill the first vessel again with water, stirring it as before: Do thus often till you find all the finest of the color drawn forth, and that none but coarse gritty stuff remains in the bottom; which when you perceive, then pour the water clear from it, and reserve the color in the bottom for use, which must be perfectly dried before you mix it with oil to work.
SPANISH WHITE: either a "pure clay," or "nothing but a chalk." Evidently, there was a considerable amount of confusion among painters as to what Spanish white was. Actually, both clay and chalk were probably sold as Spanish white. The best variety, however, was most likely composed of clay, for references speak of it as "being employed in oil painting or for varnish." 
To make the pigment from bismuth,
Put some good aquafortis into a Florence flask, and gradually add to it bismuth, broken into small pieces, till no more dissolves; then let the solution remain till it is transparent. Add to this, some water, and a white precipitate will4be formed, which is to be washed and dried ........ 
In general, whiting could be any white pigment made from a clay or chalk base. These pigments were usually named for their place of origin; thus they had many names like Bougival or Rouen white. They were used as body colors for distemper paints, but were not satisfactory in oil or varnish because they lost their lustre and darkened in color. When mixed with size and allowed to dry, they could be varnished "to look quite as bright as oil color." Another important use of the inert white pigments was as adulterants for white lead. Adulterants is perhaps a harsh word here, for it is quite possible the whiting was used as a filler and was added purposely to extend the bulk of the expensive white lead.
WHITE LEAD, CERUSE: basic lead carbonate which could be made in a number of ways. Generally, lead white was a bright white, unless it had been manufactured improperly and was, therefore, contaminated by a lead salt or some other impurity. This basic lead carbonate was one of the most important pigments available to the eighteenth-century painter.  It was used as a putty, primer, base color, and finishing color. Almost every painting job called for the use of lead white in one way or another. It was a fairly stable pigment and would stand well unless exposed to hydrogen sulfide gas which caused it to convert to black lead sulfide. Flake white was considered to be the best sort of lead white. Ceruse, another general name for basic lead carbonate, was usually considered to be a better product than what was called white lead, as the latter term was often applied to a lead white that had been adulterated with chalk.
A painter could actually make white lead with his slab and muller by following one of two simple processes. The first method was as follows:
Put one pound of litharge (yellow lead monoxide, PbO, also called massicot) on the Painter's slab, and add half an ounce of salt made into a solution with six times its weight of water; grind these two very fine, under the muller, in a state like soft mortar, and then leave it in a heap until the next day, when you will perceive it covered with white efflorescence. You now separate the mass, and grind the whole, adding water, as it may require, but sparingly, it may now be left for a few hours, but spread out on the stone, and then it must be turned, and spread out at each time of turning; each time the whiteness will increase, and, in the course of three or four days, will be a muriate of lead, which may be changed into carbonate, by saturating a vessel of water with the carbonic acid gas, by means of the sulphuric acid and carbonate of lime. 
By a second method, a painter would place lead filings on the slab with half an ounce of white sand,
add water, and with the muller grind it for the space of an hour, when you will notice a decomposition has taken place, by changing to white; and as you continue grinding it increases in whiteness, and in a few days you will have a white oxide of lead, which may be carbonized by the same means as the last. 
It was also a simple matter to prepare small quantities of white lead by the more conventional method:
Those who may wish to prepare it, should get an earthen vessel with a cover to it, and an earthen colander, with bars instead of holes, made to fit the vessel; the colander should go about half way down; then pour vinegar into the vessel till it nearly reaches the bars of the colander. On the colander place narrow slips of thin common lead rolled up into scrolls; these may be placed all over the bars of the colander, taking care that they do not touch each other. The pot is then placed over a gentle heat, and the fumes of the vinegar corroding the lead reduces it to a white calx ready for use.
The Dutch process is one of the oldest known methods of making white lead. First, thin sheets of lead were rolled up and placed in earthen pots. Usually, there was a lug or some sort of projection at the bottom of the pot to keep the coil of lead from going all the way to the bottom. The vacant space at the bottom was filled with vinegar, which supplied acetic acid. The pot was then covered and buried in a pile of dung. The decomposition of the dung generated a slight amount of heat which served to evaporate the vinegar slowly. Manure was not a very satisfactory source of heat, as it often gave off sulphur gas which combined with the lead to form a black sulphide.
The Dutch process was based on the chemical reaction that occurred when acetic acid vapor came in contact with metallic lead. Lead carbonate, or white lead, was formed when carbon dioxide gas combined with the lead. When gas was used to make white lead directly, however, a tough crust of lead carbonate was formed on the metallic lead that prevented any further corrosion. Acetic acid, on the other hand, eagerly attacked the lead, forming lead acetate. Carbon dioxide gas then replaced the acetate from the lead acetate to form lead carbonate, which, in turn, released the acetate radical to attack the metallic lead again. After the process had continued for three or four months it was completed. The corroded lead was removed from the pots and the lead carbonate was beaten off the metallic lead. After being ground and washed, the lead carbonate was ready for use.
FLAKE WHITE: supposedly the best grade of white lead available in the eighteenth century. It was made by corroding lead with "the pressings of the grape instead of vinegar." The matter cannot be ended here, however, as there seems to have been a great deal of confusion about what flake white actually was.
Besides white lead and cerise, there is another sort to be met with sometimes at the color shops, which they call flake white, which is by some accounted the best white of all others, but the reason of that I do not well understand, except it be because it is scarce and dear. 
LITHARGE, also called MASSICOT: the yellow oxide of lead. It was a stable color but rather dull. Although massicot could be prepared directly from lead by oxidizing the metal in a reverberatory furnace, if intended as a pigment, it was usually prepared from white lead. The white lead was placed in a crucible and "gently calcined" until the desired color was obtained. Like most colors made by a calcination process, the pigment could vary over a wide range of hues.
Litharge was commonly made by the direct oxidation of lead in a reverberatory furnace. It was a partially vitrified oxide available in two distinct forms. The greenish-yellow variety, called litharge or silver, was more completely vitrified. Litharge of gold, or the reddish type, was preferred as a drier because it was not as glassy as the other and, as such, was more easily dissolved in hot oil.
RED LEAD, MINIUM: prepared by oxidizing or calcining metallic lead. It could be prepared from litharge, but the best kind seems to have been made by converting lead into massicot and then changing the massicot into red lead. To manufacture red lead, the metal was placed in a reverberatory furnace "vaulted over like a baker's oven." Along each of the two side walls of the furnace, a partition rose from the floor almost to the arch above. A contemporary described the scene in this way:
. . . the coals are placed between these internal walls and the wall of the furnace, by which means the flame is drawn over the top, and reflected from the roof down upon the surface of a quantity of lead on the floor. The metal soon melts, and is altogether converted into a yellow oxide or massicot, by successively raking off the pellicles which form on the surface; this is then ground in a mill, and washed, to separate any metallic lead, by which it becomes a uniform yellow color; and after being replaced in the furnace, is exposed to the flame, while it is constantly stirred for about 48 hours, when it is converted into red lead. 
Red lead was not used very often as a red pigment. Its most important use in the finishing trades was as a priming material or as a ground for the more brilliant red colors. It was also used as a flux in the manufacture of glass and as an ingredient in lead crystal. The glassware industry created a great demand for red lead.
The most important browns were ochres or earths. The only pigments in this class that were not mined from the ground were bistre and sepia. For the most part, these colors were stable and worked well in the major media.
UMBER: a very stable brown ochre. Unburned or raw umber was a light brown in color. The pigment was often used in all types of painting although it seemed to wane in popularity -- in England at least - towards the end of the eighteenth century.  Umber was a transparent color and worked well as a glaze or a stain. It also made an excellent toning color and was used to soften the hues of the brighter pigments.
When raw umber was calcined or burned, it took on a warmer or reddish-brown color. Burnt umber was slightly easier to grind than the unburned variety, but, other than that, calcination had little effect on its physical properties.
The blacks were primarily composed of the element carbon. By far, most of the blacks available in the eighteenth century were nothing more than pure carbon. This carbon was obtained by calcining or burning a number of organic materials, and the product was named either for the way the pigment was made or the commodity it was made from.
LAMP BLACK: a permanent black made by burning resins or oils in "a confined place." When these substances were ignited in a closed chamber, such as a small sealed room, the flame was literally partially suffocated which caused it to burn incompletely and give off dense black smoke. Although there were many methods of producing lamp black, it was usually made from the dregs of colophony or the resin of the pine tree. When the waste resin was burned in a small room, the soot collected on the walls and ceiling and "once in two or three days" the pigment was gathered by sweeping it down. Lamp black was widely used by painters because "of its plenty and cheapness" and because it proved to be a "very good black for most uses."
The blues available in the eighteenth century were rather few in number. What was lacking in variety, however, was made up in quality. The blue pigments were very stable, non-poisonous, and worked well in the major media, for the most part.
CENDRE BLEUE, also called BLUE VERDITER, SANDERS BLUE: a blue pigment made by coloring chalk with blue vitriol or copper sulphate. Sanders blue was a term that was used interchangeably with blue verditer, but it was probably used on occasion to describe other blue pigments. For example, one late eighteenth century source stated that sanders blue was the name "given to an ore of copper." To make the color, chalk or whiting was added to a solution of copper in aquafortis:
A quantity of whiting is put into a tub, and upon this the solution of copper is poured. The mixture is to be stirred every day for some hours together, till the liquor loses its color. The liquor is then to be poured off, and more solution of copper is to be added. This is to be repeated till the whiting has acquired the proper color. Then it is to be spread on large pieces of chalk and dried in the sun. 
Blue verditer worked fairly well in distemper, but it did not mix well with oil as it turned "greenish or black" when wetted with that medium. However, it could be used with some success if it was added to white lead ground in oil. The white pigment lightened the blue and kept it from appearing too dark. Although blue verditer was an inexpensive color, it was generally troublesome and was used only for "coarse purposes."
PRUSSIAN BLUE, CHINESE BLUE, PARIS BLUE, BERLIN BLUE: ferric ferrocyanide, an excellent blue pigment. It was undoubtedly one of the best and most widely used blues of the eighteenth century. The pigment was used extensively in house painting and worked well with oil or distemper. It could not be used with casein paints or whitewash, however, as lime destroyed the color.
The actual discovery of the pigment is somewhat obscure. However, it seems to have been made by a Berlin colormaker, Diesbach by name, sometime during the first decade of the eighteenth century. Its discovery was announced by the Berlin Academy in 1710, but no directions were given for its preparation. A Dr. Woodward published a recipe for making the pigment in the English Philosophical Transactions in 1724, explaining that he had received the formula from a friend in Germany. Late in the eighteenth century, it was learned that Prussian blue was a compound composed of "iron oxide with a peculiar acid." The composition of this acid -- prussic acid -- was finally made known by the Swedish chemist, Carl Scheele, in two essays published in 1782 and 1783.
The first step in producing the pigment was to make the prussic acid:
Two parts of purified potass are most intimately blended with three parts of dried and finely pulverized bullock's blood. The mass is first calcined in a covered crucible, and on a moderate fire, until no more smoke or flame appears; and it is after this brought to a complete yet moderate ignition. 
The coals were cooled and dissolved in water. After filtering, the solution of prussic acid was ready to be mixed with the other ingredients to make Prussian blue. When the prussic acid solution was poured into a solution containing the proper amounts of copperas, or ferrous sulphate, and alum, a greenish blue-black precipitate settled out. When this precipitate was washed with dilute hydrochloric acid, it became Prussian blue.
INDIGO: the deepest blue color available throughout the eighteenth century. It was a product of the East and West Indies and was obtained from the Indigofera tinctoria. The plant was cut shortly before it flowered, put into vats, and covered with water. A natural fermentation process yielded a green "pulverulent, pulpy matter" which, on exposure to the air, turned blue. Before the invention of Prussian blue, indigo was . . . almost the only blue color used in painting . . . either with oil or water, except ultramarine, which, from its great price, could only be applied to very nice purposes. 
Indigo was more stable than Prussian blue, but there seems to have been great difficulty in getting it pure enough to serve as a paint pigment. In order to use indigo as a pigment, little else needed to be done to it except to make sure it was finely ground. Generally, it was used only in distemper and not in oil, for when it was mixed with oil, it would turn black. It might have been used quite frequently, however, to tint white lead ground in oil.
PEARL WHITE, OYSTERSHELL WHITE:
made by calcining oyster shells till they . . . be reduced to powder, without burning them, as it would change the color; afterwards, separate the whitest part, and levitate it with water; till it is reduced to an impalpable powder. 
On the other hand, some reliable sources state pearl white is the "magistery of bismuth, although it could also be made of calcined oyster shells." 
Until late in the eighteenth century, there were really very few green pigments available. Copper was the only metal in general use that would yield suitable green pigments. Green, however, was a color for which there was great demand in all branches of the finishing trades. Fortunately, satisfactory colors could be made in any hue desired by mixing blues and yellows together. Prussian blue usually played a leading role in the production of green colors in the last half of the eighteenth century, since it was one of the best blues available at the time.
VERT de GRIS/VERDIGRIS, DISTILLED VERDIGRIS: a green pigment made by corroding copper with acetic acid. During the eighteenth century, Montpellier, France, was a large center of verdigris manufacture. The making of this pigment was a profitable business as far back as the fifteenth century, though verdigris was known long before that. The color was made by exposing copper plates or filings to vinegar or acetic acid. Usually, copper plates were placed in jars betweens layers of fermenting grape husks. The plates, after remaining "in this situation for sufficient time," were "moistened with water" and exposed "in heaps" to the air. As the blue-green basic acetate of copper, or verdigris, formed on the copper it was scraped off and collected.
Verdigris was one of the "best" and "most useful" greens available in the eighteenth century.  It was poisonous, but was not as dangerous as the arsenic greens developed later in the century. The blue-green color of verdigris could be easily changed to a fuller green by mixing it with a little yellow. It was a fairly stable color and was used extensively in both oil and distemper. However, it was somewhat coarse, and its use tended to be confined to the commoner types of painting.
Distilled verdigris was nothing more than refined verdigris. It was made by dissolving verdigris in rectified vinegar. Once the pigment was dissolved, the solution was transferred to a second open container where it was concentrated by evaporating off some of the vinegar. Then, as the liquor was cooled, "clusters of . . . crystals of a fine deep blue-green color" were formed. It was a very good pigment, except it often turned black with time, but its high price kept it from being widely used. It worked particularly well with resin vehicles and found favor as a color used in varnish.
VERMILION, CINNABAR: a compound formed of sulphur and mercury. Cinnabar was a naturally occurring vermilion that was mined. Vermilion was the name usually given to the artificially prepared sulphide of mercury, a bright crimson pigment which was one "of the most useful colors in every kind of painting." 
Vermilion was made by subliming sulphur and mercury together, a tricky operation because of the extremely poisonous nature of mercury vapor. The "goodness" of the pigment was determined by its brightness. The actual process of manufacturing the color was still not completely understood as late as 1800:
. . . the various chemists who have written upon this preparation are not agreed respecting the proportions of sulphur which should be employed in preparing the black sulphuret of mercury or ethiops mineral . . . 
After the ethiops mineral was made, it was placed in a retort and sublimed. When the process was completed, the retort and its receiver were removed from the fire, cooled, and broken. The vermilion could then be taken out of the receiver and the neck of the retort. If the first sublimation did not produce a bright enough vermilion, it could be sublimed again.
Technically, a lake pigment can be defined as "an intimate combination" of a vegetable dye with an earthy base, formed by precipitating a dye out of solution onto the base which was usually alumina, chalk, or cuttlefish bone.  Essentially it is a white or colorless body dyed with an organic coloring matter.  The natural dyestuffs could be converted to a solid pigment phase because they were soluble in water, but when a solution of common alum, "saturated with potash," was added to a liquid dye solution, an insoluble precipitate was formed.  Most likely, the dye became absorbed on the surface of the precipitate rather than combining with it to form a chemical compound. 
Before describing a lake pigment or lakes, a few of their important properties should be noted. The colors of the various lakes, available in almost every hue, were described as "beautiful," but their use was limited because they soon faded when exposed to sunlight.  In many cases, fugitive dyes could be precipitated on insoluble bases, and the combination would stabilize the dye somewhat and keep it from fading as rapidly as it might have otherwise. Nevertheless, lakes could not be used as exterior paints because they all faded sooner or later. Lakes did not seem to work well in oil in many instances, since they tended to become transparent when wetted with oil.  This meant they could only be utilized as glazing colors if mixed with an oil vehicle. On the other hand, they could be used to make paints with substantial covering power if mixed with one of the distemper vehicles.
CARMINE: the best of the red lake pigments. It was of a bright crimson color and was made by precipitating the coloring matter of cochineal on an earthy base. To prepare the lake:
four ounces of finely pulverized cochineal are to be poured into four or six quarts of rain or distilled water, that has been previously boiled in a pewter kettle, and boiled with it for the space of six minutes or longer. Eight scruples of Roman alum, in powder, are to be then added, and the whole kept upon the fire one minute longer. As soon as the gross powder has subsided, and the decoction has become clear, it is to be carefully decanted into large cylindrical glasses covered over, and kept undisturbed till a fine powder is observed to have settled at the bottom. The liquor is then poured off from the powder which is to be gradually dried . . . 
There were many other formulas that can be followed to make carmine, but, basically, they were all the same. Carmine was quite expensive. It is impossible to say whether this was because there were few people engaged in its manufacture and therefore only available in limited quantities or whether only a few people made it because it was an expensive operation.
OILS, DRIERS, and DRYING OILS.
Oils were defined as bodies unctuous to the touch, more or less fluid, insoluble in water, and combustible.
Generally, three distinct classes of oil were recognized in the eighteenth century. The first category was animal oil, generally obtained by distillation and expression from the fatty tissues of animals. Fish oil was the only one derived from the animal kingdom that played a significant role in the finishing trades. It was not a satisfactory binding medium for paints, as it dried too slowly and tended to become rancid when exposed to the air for any period of time. Nevertheless, many attempts were made to use it in paints as a linseed oil additive.
Mineral oil, the second type, also known as rock oil, oil of petre, and naptha, was recognized as being the "thinnest of the natural bitumens." In many parts of Europe it exuded spontaneously from the ground. Although mineral oil was occasionally used as a varnish thinner, it was only consumed in negligible amounts until the second half of the nineteenth century.
The third class, vegetable oils, was by far the most important to the finishing trades. They were characterized by their liquid form, an unctuous feel, their ability to burn, a mild taste, a boiling point not under 600 degrees Fahrenheit, insolubility in water and alcohol, and their inability to evaporate completely. Generally, the fixed oils were obtained by pressing it out of the seeds or kernels of plants. Many of these oils, such as linseed, nut, poppy, and hempseed oil, were capable of drying into a solid film. Basically, the oils dried by a process of polymerization caused by the absorption of oxygen from the atmosphere. These drying oils, as they were called, were particularly important to the painter and varnisher, because they could be utilized as binders for oil base paint and as solvents and binders for making fixed oil varnishes. When a paint was made from a pigment and a drying oil binder and applied to a surface as a thin film, the oil absorbed oxygen, polymerized, and held the pigment to that surface. Similarly, when a resin was dissolved in a drying oil, the oil polymerized around the resin as it dried, thus forming a very tough, durable varnish. Though they had their shortcomings, the drying oils were among the most successful binding media and fixed oil varnish solvents available to the decorative and protective finisher until well into the twentieth century.
Of the drying oils, linseed oil was undoubtedly used the most. In spite of its faults, it was satisfactory for the majority of uses, plentiful, and inexpensive. Louisbourg's linseed oil was mainly obtained through imports from France. In New England colonial farmers began to grow flax at an early date to satisfy their domestic requirements for fiber to make cloth. As the flax seed, or linseed as it was called, was not damaged by the methods used to separate the seeds from the fiber, there was a good supply of the seed in many parts of America. By the latter part of the eighteenth century, the production of flax was increasing, and, as flax seed became more available, linseed oil mills began to spring up all over the colonies.
The first step in expressing the oil was to prepare the seed for the press by bruising it in a stamping or edge runner mill. If the seeds were pressed without any further processing, the product was called cold drawn oil. This oil was a clear, pure fluid, but it was quite expensive. The yield of cold drawn oil was low because
as it was impossible to separate the shell from the kernel, the entire seed must be submitted to the press; but if thus treated without any previous preparation, the quantity of oil obtained is comparatively small, on account of a strong mucilage that resides in the shell, and absorbs a large proportion of the oil as it is forced out of the kernel. 
One of the methods proposed to reduce the absorption of the oil by the mucilage and still draw the oil cold was to roast the seeds before pressing them. The roasting process was supposed to destroy the mucilage before the press was applied to the seed. A very effective means of increasing the yield of oil, thus lowering the price, was to press the seed between heated iron plates. The heat broke down the mucilage and facilitated the flow of the oil. This hot drawn oil, as it was called, was darker in color than the cold drawn variety. For many applications, however, such as binders for the darker pigments and solvents for the darker varnishes, its color was not a disadvantage. No matter which method of pressing the seed was used, the oil was collected in troughs as it ran off the press and directed into settling tanks. In these tanks the grosser particles of foreign material settled to the bottom. The relatively clear oil could then be siphoned off the top of the tank as it was needed.
Small bits of plant tissue and other finely divided foreign matter were difficult to settle out of the oil. One supposedly effective way to remove these small particles was to add egg white or some similar substance to the oil. When the albuminous material was congealed, it trapped the solid impurities and carried them to the bottom of the container. If this method did not remove enough of the foreign matter, the oil could be filtered.
Linseed oil's natural brown color severely limited its use as a binder for the lighter colored pigments or as a solvent for colorless varnishes. When a clear linseed oil binder or solvent was required, the oil had to be bleached before it could be used. One of the recommended ways of bleaching the oil was to:
Take any quantity of linseed-oil, and, to every gallon, add two ounces of litharge; shake it up every day for fourteen days; then let it settle a day or two; pour off the clear into shallow pans, such as dripping pans, for instance, first putting half a pint of spirit of turpentine to each gallon: place it in the sun, and, in three days, it will be as white as nut oil. 
Fuller's earth could also be used as a bleach because it had the ability to absorb the coloring matter from the oil. Many other methods were proposed for bleaching linseed oil, but none seemed to work as well as these two standard procedures.
The methods used to clear linseed oil of impurities and to bleach it did not alter its chemical or physical properties. The oil was an excellent binding medium except that it took three to four weeks for it to dry properly. To convert it into a practical and useful binder or solvent, linseed oil had to be treated to decrease its drying time. The simplest method of speeding up the drying process was to heat the oil to 220 to 280 degrees Centigrade and keep it at that temperature for several hours. This heat treatment altered the chemistry of the oil so that it dried more rapidly. Usually, metallic salts called driers were added to the oil while it was heated to the boiling point. The commonly used driers in the eighteenth century were the lead oxides, sugar of lead, and white vitriol. They acted as catalysts in that they helped the linseed oil to trap oxygen. The film dried or solidified by a polymerization process that progressed as the oil oxidized. By passing on oxygen to the oil, the driers enabled it to polymerize and thus dry much faster than it could otherwise.
All the lead oxides could be used as driers, but litharge worked much better than minium (red oxide). Another lead base drier was sugar of lead or lead acetate. It was made by dissolving litharge in hot vinegar. As the saturated solution cooled, the sugar of lead formed crystals. The crystals were removed from the liquid, and, after being drained and slowly dried, they were ready for use. Sugar of lead was utilized as a drier instead of litharge when a light-colored boiled oil was desired. Unlike litharge, it would not darken the oil during the boiling process. White vitriol or zinc sulphate was also successfully utilized as a drier. It was mined in Europe in mineral form, and its effects on linseed oil were very similar to those of sugar of lead.
Many pigments, such as the lead whites, red lead, and some ochres, acted as drying catalysts in their own right. When present in one of the fixed oils, they accelerated the drying of the oil. Conversely, pigments like the carbon blacks and Prussian blue retarded the drying of the oil.
Painters and varnishers were aware that the oil binders and solvents had to be treated in order for them to dry within a reasonable amount of time. There was no set formula for treating oil with driers. Each craftsman probably had his own favored recipe that called for boiling oil with either a single drier or a mixture of driers. Generally, if a rule of thumb can be identified in the multitude of surviving formulas, about four to five ounces of drier, or driers, was boiled with a gallon of oil. Although all recipes for making a drying oil did not call for actually boiling the drier with the oil, some sort of heat treatment was usually utilized. Most likely, this was the case as the driers dissolved more easily in hot oil. When driers were boiled in oil, a scum formed on top of the liquid during the boiling process. This scum, called facts or smudge, was a very thick material that dried quite rapidly. It was often used to make a putty for filling defects in surfaces before they were painted.
Nut oil was another drying oil that was only available in limited quantities. It was obtained by expression from the fleshy part of walnut seeds. Walnut oil did not have to be charged with driers before it would dry rapidly and completely. It was a clear oil which gave it an advantage as a binder for white pigments, as it would not darken them. Also, it was better than linseed oil for making colorless varnishes. Generally, nut oil was preferred over linseed oil, but there simply was not enough of it to supply demand. Since its supply was limited, the painter or varnisher could only get enough walnut oil to meet special needs.
Fish oils are obtained by boiling the fish and skimming off the oil. The crude oil has a brownish color and an offensive odor. Much of the oil was extracted from the cod, herring and mackerel. Fish oil is of the nondrying class, but when mixed with linseed oil was used in paints.
Spermaceti oil is a waxy oil extracted from the head cavity of the sperm-and bottlenose whale. This oil is first separated out, leaving a clear yellow oil. It can be made into a true wax by boiling the sperm oil and letting it cool. White, crystalline flakes of fatty substance then separate out, which is the wax.
The term balsam was generally applied to the resinous exudation of coniferous or cone-bearing evergreen trees. Balsams, also referred to as oleoresins, were soft semi-liquid substances consisting of a resin dissolved in an essential oil. When a balsam was distilled, the essential oil was boiled off and collected in a receiver, thus leaving the pine tree resin, usually called rosin or colophons, behind. A balsam was referred to as a turpentine, more often than not, and the distilled essential oil - what is commonly called turpentine today - was then called spirit or essence of turpentine. Balsams were occasionally used as softening agents and were added to varnishes and lacquers to make them less brittle.
COMMON TURPENTINE: extracted from the spruce fir, the long leaf and short leaf pines, and other trees of the species pinus. Generally, this balsam was procured from pine forest in southern France, Switzerland, and the southern United States. When incisions were made through the bark of the tree, the turpentine flowed out and collected in troughs cut into, or receptacles attached to, the tree. Common turpentine was of a "dark brown color," and "of the consistence of honey." Usually it was used only in the cheapest of varnishes if it was used at all. Large quantities of the balsam were consumed in the manufacture of spirits of turpentine.
STRASBURGH TURPENTINE, GERMAN TURPENTINE: a product of Germany. The balsam was exuded by a "kind of silver fir" and was of a clearer yellow-brown than the other turpentines. Strasburgh turpentine, when added to a varnish, gave that finish a brighter appearance. In other words, the balsam imparted a high gloss to a varnish film.
VENICE TURPENTINE: the most commonly used balsam. The turpentine, which varied from greenish yellow to colorless in hue, was collected from the European larch tree. The tree was tapped in the spring by boring a hole into the heart near the base. Many varnish formulas called for the addition of small quantities of Venice turpentine. The balsam did not harden rapidly on exposure to the air; thus it was used as a softener to keep the varnish from becoming too brittle on drying.
Turpentine, commonly referred to during the eighteenth century as spirit, oil, or essence of turpentine, or turps, was used both as a solvent and a thinner. The importance of turpentine as a solvent before 1750 is difficult to evaluate, however.  Turpentine was considered to be a vegetable oil, but a volatile variety referred to as an essential oil. Unlike the fixed oils, it would evaporate rather than polymerize or solidify to form a protective film.
Turpentine was used as a thinner for oil base paints and fixed oil varnishes since it possessed the ability to dilute the fixed oils, thus reducing their viscosity by dispersing them in a liquid solution. If oil paint and fixed oil varnish were brushed onto a surface without being diluted with a thinner, the film that was applied would be so thick that it would often pucker or drool before it could dry. Turpentine did not remain mixed with the oil, for once the diluted or thinned finish was applied it evaporated leaving the oil behind to polymerize. Thus, it did not serve any function other than that of bringing the paint or varnish into a proper working consistency. Turpentine was also utilized as a solvent for making what were called essential oil varnishes. Here, it was used as a solvent only because its purpose was strictly to dissolve the resins, so that they could be applied in liquid form.
Once an essential oil varnish was brushed on a surface, the turpentine evaporated completely and left nothing behind but the resin.
Turpentine was distilled from a balsam in either copper or iron stills. As the balsam was heated in the still, the turpentine was vaporized and driven off, leaving the colophony or pure resin behind. The actual distillation process was a difficult task and required a cautious and experienced workman:
The still is charged with gum at the top, and a cap is then fitted on. This cap connects by an arm with the worm, around which cool water is constantly running. When the still is filled and this connection made, the fire is applied. As the process of distillation goes on the distiller adds from time to time a little water to prevent scorching, and tries his charge by inserting a rod in a small hole in the top of the still intended for that purpose. When the process has reached a certain point he draws his fire and allows the still to cool a little; then he takes off the cap and from the liquid mass inside skims off all the chips and bark, of which there is always more or less in the gum. If the cap is taken off too soon, the whole charge will take fire from rapid oxidation. When the hot rosin (colophony) is cooled down, it is drawn off through a pipe at the side of the still near the bottom and passed through strainers into a wooden tank, from which it is dipped into barrels. Meanwhile, the spirits, being condensed in the worm, run out mingled with considerable water into a tub, the water, on account of its greater specific gravity, settling at the bottom From this tub, the turpentine is siphoned off . . . 
GUMS were thick plant juices, similar in appearance to resins, that were soluble or partially soluble in water. They were exuded by a number of plants and were "non-crystalline, structureless substances." Resins, though sometimes called gums, were not soluble in water and possessed markedly different chemical compositions. Gums were dissolved in water to form "an opake emulsive liquor" or a mucilaginous solution that could serve as a water soluble vehicle for pigments. Thus the only major use of gums in the painting crafts was as a binder for water colors.
GUM ARABIC, GUM ACADIA: the gum that was most frequently used as a binder for water colors. It was exuded by the acacia tree which grew in Egypt, in Arabia, and along the coast of Africa. Gum Arabic varied from clear white to pale yellow in color; its surface always had a "glistening appearance."
GOMME GUTTA/Percha, sob, siak, sundik, hankang, jangkar, susu: is a gum resin obtained by boiling the sap of species of trees of the order of Sapotaceae, native to Borneo, New Guinea, Malaya and Indonesia. It is grayish white, very pliable, but not elastic like rubber.
RESINS are neither soluble in nor softened by cold water. Like balsams and gums, they are very complex organic compounds consisting, for the most part, of carbon, hydrogen and oxygen. In the eighteenth century resins were usually defined by the physical properties they possessed in common as a type of organic material:
The chemical properties which are usually understood to characterize a resin, are the following: it is first softened and then melted by heat, and when kindled, it burns readily with a strong and generally fragrant smell, with copious flame and 31 smoke, and leaves scarcely any residue behind . . 
Generally, resins were secreted by the more biologically complex plants, "partly as a normal" function and "partly as the outcome of disease." In many cases, the production of resin could be increased by purposely wounding the tree.
SANDARAC, GUM JUNIPER: the product of the North African Callitris quadrivalvis. Externally it resembled mastic, but there the similarity ended. Its color varied from clear to brown. Sandarac tended to be a brittle resin, but it could be made more elastic by adding a softener to it. The resin was soluble in alcohol but would partially dissolve in turpentine. It was generally utilized in the manufacture of spirit varnishes with a mixture of other resins. Sandarac could not be used alone successfully because it made a varnish that was too soft to be serviceable.
Animal glue has been made since ancient times, and are usually water solutions of animal gelatin. Hide and bone glues are animal glues made from impure gelatin from the clippings of animal hides, sinews, horn and hoof pith, from the skins and heads of fish, or from bones. Fish glue is not usually classed with animal glue, nor is casein glue. The vegetable glues are also misnamed, being classed with the mucilages. The stiffening quality of glue depends upon the evaporation of water, and it will not bind in cold weather. It will not withstand dampness, but with white lead, or other material added it becomes partly waterproof. Casein glues are more water resistant.
In making bone glue the bones are crushed, the grease extracted by solvents, and the mineral salts removed by dilute hydrochloric acid. The bones are then cooked to extract the glue.
Fish glue is made from the jelly separated from fish oil, or from solutions of the skins. The best fish glue was made from Russian isinglass. Fish glues do not form gelatin well and are usually made into liquid glues, for use in paints and sizes. Pungent odors indicate defective glue. The glues made from decomposed materials are weak.
The base for distemper paint is the glue, made of scraps of parchment, gand (shredded leather from old gloves), and sheepskin. The scraps are soaked and washed in a large pot with 1 pound of scraps to 10 points of water. This is boiled over a hot fire for approximately 3 hours until it forms a liquid paste and the water in the pot is reduced to two thirds. This is left to cool and then poured over a piece of linen or through a sieve while it is still lightly warm. If the glue is well made it will have a consistency of a very firm, transparent gel when cooled: this will keep for about 8 days in winter and for only 4 or 5 days during the summer, provided that it is kept in a shelter, cellar, or a cool pJ2ace. No one knows how to keep it for any longer. 
STARCH is a large group of natural carbohydrate compounds occurring in grains, tubers, and fruits. The common cereal grains contain from 55 to 75% starch. Tapioca starch gives quick tack and high adhesion in glues. When cooked in water, starch produces an adhesive paste. These pastes can be mixed with gums, resins, or glue to add strength and antioxidants.
LIME is a calcium oxide occurring abundantly in nature, chiefly in combination with carbon dioxide as calcium carbonate, in limestone, marble, chalk, coral, and shells. It is obtained by heating limestone in a furnace or kiln to about 1000° F. to burn out the carbonic acid gas. The residue is called quicklime or caustic lime. Pure quicklime is white and amorphous or crystalline. Oystershells have about the same calcium carbonate content as the best grade of high-calcium limestone, with low impurities, and they are used for making quicklime.
CHALK: a soft carbonate of lime. The first step in processing it was to break it up under a runner stone. Then it was washed, formed into cakes, dried and sold. It was used for
the common white-washing of apartments . . . but gypsum is far superior. It serves also for different grounds, either colored or not, which are applied in distemper. 
Chalk could not be mixed with oil successfully, because it would cause the film to split and crack on drying. Also, it could not be used as a priming material, some painters believed, because a mixture of white lead and pipe clay worked much better and was much more permanent. 
CHINA CLAY, PIPE CLAY, KAOLIN, BOUGIVAL WHITE, ROUEN WHITE: a product that was mined directly from the earth. It was hydrated silicate of alumina, essentially, with a complicated chemical composition. China clay was dug from naturally occurring deposits and required little more than washing and drying before it could be used. Painters preferred this type of whiting, when pure, over the chalks, because it worked better both as an extender and as an ingredient in the priming coats. 
There were a number of inert white substances that seem to have been part clay and part chalk -- Bougival and Rouen white, for example. These materials were favored over the chalks but were not as good as the purer clay pigments.
TAR for caulking ships was obtained in the destructive distillation of coal, peat and wood. Pine tar is a by-product in the distillation of pine wood. Pitch is a composition of gum or resin and other glutinous substances, which make a hard, dry and blackish solid, and is the tar with the pine-tar oil removed and can vary from medium hard to solid. (Brai sea and Brai bras). Goudron was derived from Pine trees. The tree was tapped and the balsam collected. To make tar, the balsam was simply ignited and allowed to burn until it thickened into the desired product. It came in barrels and it had an oily consistency, yellowish in color. The balsam was also distilled in stills so that the turpentine could be captured and condensed. By the end of the eighteenth century, turpentine was becoming a valuable product.
X. The tar (goudron) shall have a fine and liquid grain, and not be burnt or have any admixture of filth or water; that of Weybourg, of oak barrelling, shall be preferred to any other, except that of the Kingdom, in the dockyards where it may be had.
The tar. Article XI of Title II of the Regulation of 1674 stipulates that all goods of this quality be taken from and bought within the Kingdom.
XI. Pitch must be clean, greasy, black and sticky; none shall be received from foreign countries except the crowned variety from Stockholm, and that of Weybourg. That which is made in France shall always be preferred.
Pitch (brai) is a composition of gum or resin and other gluey materials, which forms a hard, dry, blackish body. Caulkers melt it to apply to the layers of oakum with which they fill the joints the planks which make up the side of the vessel. 
WOOD TAR from the destructive distillation of other woods is a dark-brown viscous liquid used as a preservative, deriving this property from its content of creosote, it was obtained from the crude distillation of pine stumps and roots.
TALLOW is a general name for the heavy fats obtained from all parts of the bodies of sheep and cattle. The tallows have the same general composition as lard, but are higher in the harder saturated acids. It comes as a nearly white, odorless paste.
SULPHUR is obtained from volcanic deposits in Sicily, Mexico, etc. It forms a crystalline mass of a pale-yellow color.