Dimethyl ketone, commonly called acetone, is an organic solvent obtained as one of the products of the destructive distillation of wood. Chemically speaking, ketones are secondary alcohols (such as isopropyl alcohol) that have been oxidized. Methyl ethyl ketone (MEK) is another member of this family which is sometimes used as a solvent for vinyl plate lacquers.

Acetonee is a colorless liquid, boiling at 65,2° C and possessing a characteristic pungent odor and sweet taste. Although it is infrequently used in hand lithography, it is capable of producing unique results when combined with mixtures of water tusche. Minute quantities of acetone, when added to water tusches, will destroy the emulsion balance between their fatty-acid particles and vehicle. The grease particles are thrown out of the solution in the form of clotted globules. The substance, when drawn with a brush, will produce a coarse and blotchy appearance that cannot be obtained by other means. It is sometimes useful to create powerful and primitive drawing effects.
It is also used in several special lithographic techniques.

Many types of limestone have been used in lithography, but by far the best is the stone that comes from Solnhofen in Bavaria, sometimes called Kellheim stone. The superiority of this stone is due to its fine and uniform molecular structure, which leads to a stable and consistent reaction to the processes of drawing, etching, and printing. The smallest stones were originally used for vignette drawings and illustrations, the largest for posters and billboards. In limited quantities, some stones are still being quarried today. Through the years, stones of the larger sizes have become increasingly difficult to find; and the shortage may be expected to become still more critical in the future.

Solnhofen stones are harder and more brittle than other limestone. Because of this, they are easily chipped and broken, and should be handled with care. Their texture is compact yet porous and they will retain moisture on their surface for considerable periods of time.

Stones vary in color from yellow or buff to a blackish gray. Their color is an index to their hardness: the darker the color, the harder the stone. In general, the harder stones are best suited to lithographic printing. Because of the difhculties encountered in working on dark gray stones, particularly the distortion of value relations, light gray stones should be used whenever possible for delicate or complex work. The softer buff and yellow stones should be reserved for drawings having relatively simple tonal values. Few stones are perfect. Many stones, however, have only minor defects to which no special attention need be paid. Many light-colored stones have red iron marks or stains. These have no effrect on drawing or printing, and such stones are completely usable. “Chalk marks,” or a gray-wbite mottling on the surface, present a more difficult problem. The whitish areas are frequently soft and tend to grind and etch unevenly. Stones so marked should be discarded or used only for simple work. Feldspar crystals often appear in the surface of stones. These crystals, since they have no affinity for grease, will print as white spots. Usually they appear in small groups or clusters, making it possible to work around them. When this cannot be done, another stone should be chosen.

The most common defects found in stones are tiny veins, which appear as hairline cracks differing from the surrounding stone in color and hardness. These may be very troublesome. At times they will print as faint white lines; at times they will take ink and print as black lines; at other times they will not affect the work. They are to be tolerated unless their effect is disruptive to the image.

Most limestone was formed during the Jurassic middle period of the Mesozoic era, between 136 million and 190 million years ago. Limestones used for lithography are described as being nonclastic, i.e., not composed of fragments of existing stone.
Instead, they contain microfragmentations of various forms of marine life (minute crustacea, protozoa with calcite shells, and certain coral-forming organisms) deposited in calcareous mud (micrite) on the sea floor. Pressure, heat, and chemical reaction compacted the calcareous deposits. In the formative cycle, one stratum of sediment was deposited over another, further compacting the earlier layers. During diastrophic periods, the earth’s crust was deformed, and the sediments of the sea floor were elevated and subjected to subatrial erosion. During the periods of elevation, rivers and streams intermixed other chemical components with these deposits. After formation, the limestone strata in most other parts of the world were subjected to additional cyclic subsidence and uplift. Each such disturbance produced joints and faults in the normally horizontal stratum, permitting the formation of other minerals by hydrothermal alteration and weathering.
Two major geologic factors seem to be responsible for the unique properties of the Solnhofen deposits, First, owing to unusual regional circumstances, only a very small percentage of mineral impurities combined with the calcareous deposits during their formation. Second, the horizontal strata of the deposits of limestone remained relatively stable during the various epochs of cyclic upheaval.
Massifs of coral limestones correspond to the position of ancient reefs and are in juxtaposition with well stratified, fine grained limestones, exploited as lithographic stone. The famous quarries of Solnhofen have provided rare but precious impressions of swimming and aying animals (fish, crustaceans, flying reptiles), fallen on the muddy bottom and fossilized with an extraordinary delicacy of detail. There existed at that point, no doubt, tranquil lagoons in the middle of atolls or protected by reef barriers.

Lithographic stones have a close and compact, yet porous texture. They should be handled with care, because they are very hard and brittle; when they break, they part cleanly with a conchoidal fraeture.

Stones must have a certain thickness, depending on over-all size, to withstand the pressures of the printing press without breaking. Small stones up to 22 x 35cm should have a minimum thickness of 5 cm. Larger stones require 7 to 10 cm of thickness for safe printing. Thinner stones are often backed with slate to prvide sufficient bulk to withstand printing and to prolong their usefulness.
The color of a stone indicates its hardness and quality.

Chemically, lithographic stones of the finest quality contain approximately 94 to 98 % calcium carbonate and carbon dioxide. The remain ing 2 to 6 per cent of foreign matter is mostly composed of silica, iron, manganese, and aluminum oxide. Because of its extremely small percentage of chemical impurities, the stone can absorb grease or water with equal affinity; meanwhile it responds to the chemicals used in lithography with maximum sensitivity.

When the stone is etched with solutions of gum arabic and nitric acid, its chemical compsiticon enables the printing image to be established in the following two ways:

1 – The fatty bodies of the drawing materials are con-verted by chemical action into fatty acids; these combine with the calcium of the stone to form insoluble lime soaps that are highly receptive to greasy printing ink.

2 – The surfaces without grease drawing are changed from calcium carbonate to calcium arabinate by virtue of the adherent gum arabic film produced by etching and drying the stone. The adsorbent gum has the property of keeping the stone surface moderately damp when mois- tened with water. In this way the stone’s natural affinity for water retention is increased considerably by the etch-ing process. When the residue of the drawing components is washed away with water and turpentine, the latent lithographic image can be faintly seen like a photographic negative. The difference in color between the image and nonimage areas is the result of the calcium oleate image formation and the calcium arabinate nonimage formation.

The reliability of these lithographic functions is related directly to the chemical composition of the stone itself.

Both image and nonimage formations are impaired if high percentages of foreign impurities are present. For example, concentrations of silica, alumina, magnesia, or quartz, being less porous than calcium carbonate, will resist somewhat the absorption of fatty image particles as well as the chemical reaction of desensitizing etches. Thus, image formation in areas containing such impurities will be weak or nonexistent and the tonal gradations of the drawing will be coarsened or disrupted. These conditions are particularly evident when working with soft yellow and white stones, which are high in impurities. It should now be evident why other types of limestone, which have even greater percentages of impurities, are unsatisfactory for lithography.

Silicon carbide is a ceramic compound of silicon and carbon. In lithography carborundum is used to grain the stone.

Most silicon carbide is man-made for use as an abrasive (when it is often known by the trademark carborundum), or more recently as a semiconductor and moissanite gemstones. The simplest manufacturing process is to combine silica sand and carbon at a high temperature, between 1600 °C and 2500 °C.
The material formed in the Acheson furnace varies in purity, according to its distance from the graphite resistor that is the heat source. Clear, pale yellow and green crystals have the highest purity, and are found closest to the resistor. The colour changes to blue and black at greater distance from the resistor, and these darker crystals are less pure, and usually doped with aluminium or iron, which increases electrical conductivity.

Purer silicon carbide can be made by the more expensive process of chemical vapor deposition (CVD). Commercial large single crystal silicon carbide is grown using a physical vapor transport commonly known as modified Lely method. Purer silicon carbide may also be made by the thermal decomposition of a polymer, poly(methylsilyne), under an inert atmosphere at low temperatures. This has certain advantages over the CVD process in that the polymer may readily formed into various shapes prior to thermolization into a silicon carbide ceramic.

Alpha silicon carbide (α-SiC) is most common, and is formed at temperatures greater than 2000 °C. Alpha SiC has the typical hexagonal crystal structure. Beta modification (β-SiC), with a face-centered cubic crystal structure, is formed at temperatures of below 2000 °C, but has relatively few commercial uses. Silicon carbide has a specific gravity of 3.2, and its high melting point (approximately 2700 °C) makes silicon carbide useful for bearings and furnace parts. It is also highly inert chemically. There is currently much interest in its use as a semiconductor material in electronics, where its high thermal conductivity, high electric field breakdown strength and high maximum current density make it more promising than silicon for high-powered devices. In addition, it has strong coupling to microwave radiation and that, together with its high melting point permits practical use in heating and casting metals. SiC also has very low thermal expansion coefficient and no phase transitions that would cause discontinuities in thermal expansion.

Pure SiC is clear. The brown to black color of industrial product is caused by iron impurities. The rainbowish lustre of the crystals is caused by the passivation layer of silicon dioxide that forms on its surface.

Lithographic crayons are available in several forms and degrees of hardness. They can be obtained in short sticks, tablets, and pencils. A numbering system is employed to identify degrees of hatrdness, ranging from #00,the softest and the greasiest, to #5, the hardest (american scale, in french scale: #5 is the softest and #00 is the greasiest). The very soft crayons and pencils produce rich, smoky black; the harder ones (containing less grease) produce the lighter and finer tones. Exprience ir drawing and printing will quickly indicate those grades best suited to individual needs.

It is well to remember that the consistency of the crayon will affect the character of the drawing as well as the printing. The surface of the lithographic stone is hard and abrasive. Even the hard crayons do not long retain a point or edge, and the softer crayons become blunt in the course of drawing a single line. Soft crayons thus lead to a “mushy” line; harder crayons give a crisper effect.

Crayon tones are traditionally built up slowly, starting with a hard crayon and gradually moving to softer as darker tones are reached. The slow, repetitive stroking of the stone with the crayon builds up a beautiful bloom that can range from the most delicate silver-gray to the softest velvety black. The luminosity that can be obtained through this method is unobtainable through any other.

The sequential use of first hard and last soft crayon, has a technical as well as an aesthetic justification. If the sequence is reversed, applying hard crayon over soft, the work may look darker but will not print that way.The reason for this is the soft crayon has allready impasted its maximum grease to the stone, and the harder but less greasy crayon on top can add no more. It will create the illusion of darker looking work, but this is an optical rather than a chemical effect and will be lost in printing. In drawing with lithographic crayons and pencils, the artist will notice several ways in which they differ from ordinary drawing materials. When tones are put on with back-and-forth strokes, it will be seen that the crayon tends to pick up work at the end of each stroke, leaving a small white dot. The firmer the stroke and the softer the crayon, the more this is so. This effect is due to the tackiness of the crayon. Crayon clings to crayon more readily than to stone, particularly at the maximum point of pressure, usually at the beginning or the end of a stroke. Over large areas, such tiny white marks may give an unpleasant salt-and-pepper look to an otherwise even tone. This can be avoided by stroking in one direction only, with the crayon in motion both before and after it touches the stone.

Soft crayons, when used on the side and stroked rapidly an with heavy pressure, will give a coarse, raspy appearance because of the way in which crayon particles cling to one another as the tone is built up. This effect, like all others inherent in the nature of the materials, may be utilized when appropriate.

The crayon, because of its fragile structure, should always be sharpened by cutting away from the point rather than toward it. When working with sharpened crayons, metal crayon holders make work much easier. It will be found that extremely dark accents, particularly over established tones, will best be achieved by pushing rather than pulling the crayon across the stone. The pressure thus exerted tends to squash the crayon more firmly into the stone. Soft crayons held perpendicularly and pulled rapidly will skip or hop, producing a jumpy or dotted line.

Crayons are soluble in water, turpentine, and other solvents. Drawing through films of these solvents on the stone will produce varying effects somewhere between those of a pure wash and a pure crayon drawing. The more solvent is present, the more crayon fis dissolved, ultimately leading toward a wash. The character of the wash is conditioned not only by the type of solvent used, but also by the softness of the crayon and by the amount of solvent.

Lithographic tusche is available in three forms: stick, paste, and liquid. Although the three are compounded of basically similar materials, each has subtly different characteristics. The stick and paste tusches are more flexible in that they may be used with water, turpentine, or a petroleum solvent.

In general, tusche mixed with water flows more freely and dries more slowly. Tusche mixed with other solvents tends toward greater viscosity and penetrates more deeply into the stone. The image so produced, being more deeply seated, is richer and more resistant to etching than the image made with water tusche. As a result, solvent-tusche images have a tendency to print darker than they appear in the drawing. Tusche, when diluted with either water or solvent, is extremely sensitive to the slightest variations in use. Careless handling leads to uncertain and unpredictable results. In the hands of an experienced lithographer, however, tusche is a fine and versatile material with an all-butinfinite range of uses.

Before a liquid tusche is used, the bottle should be well shaken to ensure an even suspension of the liquid. Water tusche in any form should be diluted only with distilled water. Tap water contains minerals that may affect either the stability of the tusche, causing it to separate, or its greasiness. Should lime be present in the water used to dilute tusche, the greasiness of the mixture will be reduced, leading to a pale and unpredictable image.

Stick or paste tusches also may be mixed with distilled water. The best way to prepare stick tusche is to rub it vigorously against a dish or saucer. Heating the saucer first by holding it against an incandescent light bulb for a few moments will cause the tusche to soften and make the process easier. Water is then added a few drops at a time, and the tusche is worked up with the fingers or a brush.

Paste tusche can be mixed easily with water, using a brush or a palette knife. There is no objection to adding a few drops of water directly to the tusche in the can. If this is done, however, the same can should not be used later for mixing tusche with other solvents. One can of tusche should be used for water mixtures and a second can for solvent tusche.

Gum arabic is one of the most important image desensitizers used in lithography. It displays two important properties: (1) it is hydrophilic (water-loving), hence, its coatings are more receptive to water than to the fatty contents of printing ink; (2) its dried coatings, although water-soluble, hold tightly to the nonimage areas of the printing surface. A good desensitizing agent should be capable of dissolving in water and leaving a microscopic water-receptive layer on the printing surface. This layer cannot be removed even with further additions of water. Many other natural and syntetic material are hydrophilic, and some are capable of adsorption on the printing surface. Some of these are gum tragacanth, cherry gum, larch gum, mesquite gum, carbohymethyl cellulose, dextrines, alginates… With the exception of CMC, none is so effective a lithographic desensitizer as gum arabic.

Gum arabic is obtained from the dried gummy substance of the acacia tree, wich grows in Arabia, Senegal, Egypt, India, and the Sudan. This particular vriety seems to have superior properties for lithography. The gum exudes naturally from the trunk and branches of the tree in the form of tears, which harden when exposed to air. These tears are separated from the bank and sand, and, after being sorted and graded for quality, are packed for shipment.

Gum arabic falls in the class of noncrystalline carbohydrates that form colloidal solutions. Chemically, gum arabic is usually considered to be a mixture of calcium, potassium, and magnesium salts of arabic acid with some free arabic acid. When nitric or phosphoric acid is added to gum arabic to make lithographic etches, most of the salts of the arabic acid are converted to free-acid form. In this condition the sollutions produce the most effective desensitization.

Pure gum arabic can be obtained from lithographic suppliers in powdered, crystalline, or liquid form. The liquid form is formulated particularly for offset lithography; it is, however, by far the most efficient for handprinting purposes as well. Research has shown that gum arabic solutions perform best for alI-round use when they are low in viscosity and high in solid content. The advantages of commercially prepared liquid gums are many. These gums are clean and free from residue, are of controlled formulation (which ensures that each batch is exactly the same), and, more important, they are nonsouring, so that stock solutions can be kept for indefinite periods of time.

Powdered and crystalline forms of gum arabic can be liquefied by mixing with water. Although band-prepared solutions of gum arabic rarely have the same consistency from one batch to another, it is well to know how they are made.

Powdered rosin, sometimes called rosin flour, is produced as a distillate of turpentine, It is used in lithography as an acid resist to protect drawn and inked images from the corrosive action of acids used in gum arabic etches. Although other materials have been used for this purpose, none function with the over-all properties of rosin. Rosin powder is avalaible in several different qualities. The finely ground powder is the best for lithographic use. Coarser grades contain gritty particles that can scratch drawings during application. Like talc, it can be dispensed from large metal salt and pepper shakers distributed over the printing surface with a tuft of cotton or soft brush.

Talc or talcum is a clay mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. In loose form, it was one of the most widely used substances known as baby powder, along with corn starch. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage, and the folia are not elastic, although slightly flexible.

Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 1 as the hardness of talc.
As such, talc can easily be scratched by a fingernail. Talc has a specific gravity of 2.5–2.8, a clear or dusty luster, and is translucent to opaque.
Talc is not soluble in water, but is slightly soluble in dilute mineral acids.[citation needed] Its color ranges from white to grey or green and it has a distinctly greasy feel. Its streak is white.

In lithography it is used, like rosin, as an acid resist on stone and metal plates, although it is less resistant tha rosin. When used with rosin, talc lessens the surface tension of the printing element in the presence of watery solutions of gum arabic or acid. Talc can sometimes be used alone as an etch resist when acid etches are relatively weak. It is also employed thoughout the shops as an clearing agent, to dust the hands, press box, paper table, ink slab or color roller after use.

Nitric acid (HNO3), also known as aqua fortis and spirit of niter, is a highly corrosive mineral acid.

Nitric acid is one of Ihe most important chemicals in the lithographic workshop. It is manufactured mostly by the Ostwald process, which oxidizes ammonia through a series of conversions from nitric oxide to nitrogen dioxide, and then to nitric acid. The concentrated chemical is a colorless liquid, commercialy available in several grades. The grade listed as “C.P.” is preferable for lithography, although “A.R.” grades are also satisfactory.

Nitric acid by itself or in solutions of water, gum arabic, or other chemicals. It chemically prepares stones by stabilizing or altering their printing images. Mixtures of the acid and gum are called etches, and, when applied and dried on the lithograph stone, they desensitize its surface to resist additions or encroachment of grease. Concentrated mixtures of the acid in either gum arabic or water attack the stone most energetically and set free carbonic gas in violent effervescence. These strong mixtures physically attack the surface of the stone and its grease content as well and thus can alter the image quality and its tonal values by eroding the grain of the printing surface.

Nitric acid is a highly corrosive chemical which must be kept in glass- or plastic-capped bottles. It should always be handled with great caution. It should be stored along with the other acids in a specially designed acid cabinet whose wooden construction and open shelving will withstand the corrosive action of acid fumes.

For daily use the acid is funneled with a glass funnel into a 100 ml, glass-stoppered laboratory drop bottle. When this acid is being mixed with water, the water must always be poured first; the acid is added afterwards. Because of the lower specific gravity ot water, a violent splashback would occur if the acid were poured first and the water added. Painful burns can result from such a splashback. Care should be taken to prevent contact of acid solutions with the skin and clothing and to avoid excessive inhalation of the vapors. In the event of contact, the area involved should be quickly and thoroughly flushed with water. Minor skin burns can be treated by an application of household baking soda (which should always be on hand in the acid cabinet). Serious injuries should always be attended to by a physician.

Except of lithotine, turpentine is the chief solvent used in the lithography workshop. Gum spirits of turpentine is a slightly oily liquid obtained by the dry distillation of natural resins of southern pines. Steam-distilled turpentine is obtained by the steam distillation of the resinous wood from the trees. Either type is satisfactory for lithography, although the gum spirit is preferable because of its less objectionable odor.

Turpentine is an excellent grease solvent and evaporates reasonably quickly. It may be used for washing out work on stone or metal plates and may be incorporated in tusche mixtures for drawing purposes. Upon aging, it absorbs oxygen, forming a resinous substance that remains in the solution but is not volatile. Most commercial turpentines contain 1 to 4 % of this resinous substance, which is beneficial to lithography. When the printer washes the ink from the printing surface with turpentine, most of the solvent evaporates, but the nonvolatile resinous part remains as a thin coating on the image areas. This allows them to accept ink readily, which they do not do when petroleum solvents such as benzine or gasoline are used for the washout.

Asphaltum is a bituminous product of petroleum cracking. It is manufactured in crystalline and liquid form and is particularly noted for its resistance to acids. The liquid form is used in lithography primarily as an ink base for stones and metal plates. It is available either in heavy viscous consistency which must be diluted with benzine or turpentine or in thin consistency especially compounded for ordinary use as an ink base. The heavier consistency of asphaltum can be employed for special drawing techniques.

Shellac is a brittle or flaky secretion of the lac insect Coccus lacca, found in the forests of Assam and Thailand. Freed from wood it is called “seedlac.” Once it was commonly believed that shellac was a resin obtained from the wings of a bug (order Hemiptera) found in India. In actuality, shellac was obtained from an excretion of the female bug, harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk. Unfortunately there is a risk that the harvesting process can scoop the bug up along with the secretion, leading to its death.

When purified, the chemical takes the form of yellow/ brown pellets, this possibly providing the basis for the “Wing Source Story.” Shellac is a natural polymer and is chemically similar to synthetic polymers, thus it is considered a natural plastic. It can be molded by heat and pressure methods, so it is classified as thermoplastic. It was used beginning in the mid-19th century to produce small goods like picture frames, boxes, toilet articles, jewellery, inkwells and even dental plates.

It is soluble in alkaline solutions such as ammonia, sodium borate, sodium carbonate, and sodium hydroxide, and also in various organic solvents. When dissolved in acetone or alcohol, shellac yields a coating of superior durability and hardness and is available in numerous grades. It is used in the traditional “French polish” method of finishing furniture, and fine viols and guitars. Orange shellac is bleached with sodium hypochlorite solution to form white shellac. Because it is compatible with most other finishes, shellac is also used as a barrier or primer coat on wood to prevent the bleeding of resin or pigments into the final finish, or to prevent wood stain from blotching. Lightly tinted shellac preparations are also sold as paint primer.

As it is edible, shellac was used as a glazing agent on pills or candies. For this purpose, it has the food additive E number E904. There are concerns that, as it may contain crushed bugs, this coating is not vegetarian. In the tablet manufacture trade, it is sometimes referred to as “beetlejuice” for this reason.
Shellac was also used in the production of gramophone (phonograph) records until about 1950. See gramophone record for details. It is now considered obsolete as a moulding compound, having very few applications. However, it is still used as fruit coating to prevent post-harvest decay.
It is frequently used in dental technology for the production of custom impression trays.

Magnesium carbonate is a fluffy white powder produced by the precipitation of mineral magnesite. It is used as an additive to color lithographic ink to stiffen and shorten its body. It may also be used to dust over printed work that is drying too slowly.

Citric acid is a weak organic acid found in citrus fruits. It is a good, natural preservative and is also used to add an acidic (sour) taste to foods and soft drinks. In biochemistry, it is important as an intermediate in the citric acid cycle and therefore occurs in the metabolism of almost all living things. It also serves as an environmentally benign cleaning agent and acts as an antioxidant. Citric acid exists in a variety of fruits and vegetables, but it is most concentrated in lemons and limes, where it can comprise as much as 8% of the dry weight of the fruit.

The physical properties of citric acid are summarized in the table at right. The acidity of citric acid results from the three carboxyl groups COOH each of which can lose a proton in solution. If this happens, the resulting ion is the citrate ion. Citrates make excellent buffers for controlling the pH of acidic solutions.
In lithography citric acid is used in counteretching process (couteretching solution contains 1 spoon of citric acid disolved in 300 ml of cold water).

Citrate ions form salts called citrates with many metal ions. An important one is calcium citrate or “sour salt”, which is commonly used in the preservation and flavoring of food. Additionally, citrates can chelate metal ions, which gives them use as preservatives and water softeners. At room temperature, citric acid is a white crystalline powder. It can exist either in an anhydrous (water-free) form, or as a monohydrate that contains one water molecule for every molecule of citric acid. The anhydrous form crystallizes from hot water, while the monohydrate forms when citric acid is crystallized from cold water. The monohydrate can be converted to the anhydrous form by heating it above 74 °C. Chemically, citric acid shares the properties of other carboxylic acids. When heated above 175°C, it decomposes through the loss of carbon dioxide and water.

Alcohols represent the first stage of oxidation of hydrocarbons in which one or more hydrogen atoms are replaced by hydroxyl groups. This methyl alcohol is derived from methane by synthesizing carbon monoxide or carbon dioxide. Ethyl alcohol is derived from ethane by fermentation of corn, potatoes, rye, and molasses. Methyl alcohol, methanol, or wood alcohol is a colorless liquid boiling at 64,7° C. It is very poisonous when its vapors are breathed in quantities; however, because of its low cost, it is used as a thinning agent in shellac coatings employed in techniques of image transposition. It may also be used in place of acetone for destroying the emulsion balance of water tusches. Ethyl alcohol, ethanol, or grain alcohol is seldom necessary for use in hand-printing processes.