§ 29.

PART III.-THE TECHNIQUE OF PAINTING The Materials of Painting.-Painting begins, as we have seen, on the one side in outline delineation, on the other in the spreading of a coating of colour on a surface. For both these the material apparatus is ready at hand. Drawing may have begun merely with lines in the air, but lasting designs were soon produced either by indenting or marking any soft substance by a hard point, or by rubbing away a comparatively soft substance, such as a pointed piece of burnt wood, on a rough surface of harder grain. Almost all the materials in use for drawing are of primitive origin. Charcoal, coloured earths and soft stones are natural or easily procured. Our plumbago was known to Pliny (xxxiv. 18) and to Cennino (ch. 34), but it was not in common use till modern times. The black-lead pencil is first described as a novelty in 1565 (Quellenschriften edition of Cennino, p. 143). A metal point of ordinary lead or tin was used in medieval MSS. for drawing lines on parchment, or on a wooden surface previously whitened with chalk (Theophilus, II. ch. xvii.). Silver-point drawing is only a refinement on this. The metal point is dragged over a surface of wood or parchment that has been grounded with finely powdered bonedust, or, as in modern times, with a wash of Chinese white (Cennino, ch. 6 seq.; Church, 292), and through the actual abrasion of the metal leaves a dark line in its track. Pliny knows the technique (xxxiii. 98). When a coloured fluid was at hand a pointed stick might be used to draw lines with it, but a primitive pen would soon be made from a split reed or the wing-feather of a bird.

The coating of one substance by another of which the colour is regarded from the aesthetic standpoint is the second source of the art of painting. To manipulate the coating substance so that it will lie evenly; to spread it by suitable mechanical means; and to secure its continued adherence when duly laid, are by no means difficult. Nature provides coloured juices of vegetable or of animal origin, and it has been suggested that the blood of the slain quarry or foeman smeared by the victor over his person was the first pigment. To imitate these by mixing powdered earths or other tinted substances in water is a very simple process. Certain reeds, the fibres of which spread out in water, were used as paint-brushes in ancient Egypt. A natural hare's-foot is still employed in theatrical circles to lay on a certain kind of pigment, and no great ingenuity would be required on the part of the hunter for the manufacture of a brush from the hair or bristles of the slain beast. In the matter of securing the adhesion of the coating thus spread, nature would again be the guide. Many animal and vegetable products are sticky and ultimately dry hard, while heat or moisture thins them to convenient fluidity. Great heat makes mineral substances liquid that harden when cold. Hence binding materials offer themselves in considerable abundance, and they are of so great importance in the painter's art that they form the basis of current classifications of the different kinds of painting.

§ 30. The Surfaces covered by the Painter.-Many important questions connected with the technique of painting depend on the nature of surfaces; for the covering coat-though from the present point of view only of interest aesthetically-may, as we have seen, originally serve a utilitarian purpose. The surface in question may be classed as follows: the human body; implements, vessels, weapons, articles of dress; objects of furniture, including books; boats and ships; walls and other parts of buildings; panels and other surfaces prepared especially or entirely to be painted on.

The differences among these from the present point of view are obvious. The body could not suitably be covered with a substance impervious to air and moisture; the coatings of a clay vessel and of a boat should on the other hand make them waterproof. The materials used in building often require protection from the weather. The painting on the prepared panel needs to resist time and any special influence due to location or climate. All such considerations are prior to the questions of colour, design, or aesthetic effect generally, in these

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coatings; and on them depend the binding materials, or media, with which the colouring substances are applied. The case of one particular surface much employed for pictorial display is exceptional. This is the wall-plaster so abundantly used for clothing an unsightly, rough, or perishable building inaterial, like rubble or crude brick. This function it performs perfectly when left of its natural white or greyish hue, but its plain unbroken surface has seemed to demand some relief through colouring or a pattern, and the recognition of this led to one of the most important branches of the art, mural painting. Now lime-plaster, if painted on while it is still wet, retains upon its surface after it has dried the pigments used, although these have not been mixed with any binding material. On all other surfaces the pigments are mixed with some binding material, and on the character of this the kind of painting depends. There is thus a primary distinction between the process just referred to and all others. In the former, pigments, mixed only with water, are laid on while the plaster is wet, and from this "freshness" of the ground the process is called by an Italian term, painting" a fresco or on the fresh," though in ordinary parlance the word "fresco" has come to be used as a noun, as when we speak of the "frescoes" of Giotto. Furthermore, as "fresco " is the wall-painter's process par excellence the word is unfortunately often employed inaccurately for any mural picture, though this may have been executed by quite a different process. In contradistinction to painting "a fresco" all other processes are properly described by the Italian term "a tempera," meaning "with a mixture." The word is used as a noun in the sense of a substance mixed with another; but it is to be regarded as the imperative of the verb temperare, which both in Latin and Italian means " to divide or proportion duly," "to qualify by mixing," and generally to regulate." Tempera means strictly " mix," just as" recipe," also employed as a substantive, is an imperative meaning "take." In ordinary parlance, however, the word tempera is confined to a certain class of binding materials to the exclusion of others, so that the more general term "media" is the best to employ in the present connexion. We go on, therefore, to consider these various media in relation to different surfaces and conditions.

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§ 31. Binding Materials or Media.-The fundamental distinction among media is their solubility or non-solubility in water, though, as will be seen presently, some possess both these qualities. The non-soluble media are (1) of mineral, (2) of vegetable origin. (1) Of the former kind are all vitreous pastes or pottery glazes, with which imperishable coloured surfaces or designs are produced on glazed tiles used in the decoration of buildings, on ceramic products, and in all processes of enamelling. Silicate of potash, employed to fix pigments on to mural surfaces of plaster in the so-called "stercochrome" or water-glass processes of wall painting (see § 37), is another mineral medium, so too is paraffin wax. In the process called (unscientifically) "fresco secco," in which the painting is on dry plaster, lime is used as a binding material for the colours. Its action here is a chemical one (see § 36). (2) Non-soluble vegetable media are drying oils, resins, waxes (including paraffin wax, which is really mineral). In ancient times wax, and to some small extent also resins, were used as a protection against moisture, as in shipbuilding and some forms of wall-painting. Resins have always remained, but wax gradually went out of use in the earlier Christian centuries, and was replaced by the new medium, not used in classical times, of drying oil. In northern lands the desire to protect painted surfaces from the moisture of the air led to a more extensive use of oils and resins than in Italy; and it was in the Netherlands that in the 15th century oil media were for the first time adopted in the regular practice of painting, which they have dominated ever since.

The soluble media are of animal and vegetable origin. Egg, yolk or white, or both combined, is the chief of the former. Next in importance are size, gained by boiling down shreds of parchment, and fish glue. Egg is the chief medium in what is specially known as "tempera" painting, while for the painting

Attention must be drawn to the fact that substances can be prepared for use in painting that unite soluble and insoluble media, but can be diluted with water. These substances are known as 66 emulsions." A wax emulsion, which is also called "saponified wax," can be made by boiling wax in a solution of potash [in the proportions 100 bleached wax, 10 potash, 250 distilled water (Berger, Beiträge, i. 100)] till the wax is melted. When the solution has cooled it can be diluted with cold water. An admixture of oil is also possible. This, according to Berger, is what Pliny and Vitruvius (vii. 9, 3) call " Punic wax," a material of importance in ancient painting.

An oil emulsion can be made by mixing drying oil with water through the intermediary of gum or yolk of egg. An intimate mechanical compound, not a chemical one, is thus effected, and the mixture can be diluted with water. If gum arabic be used the result is a "lean "emulsion of a milky-white colour, if yolk of egg a "fat" emulsion of a yellowish tint. When these wax or oil emulsions are dry they have the waterproof character of their non-soluble constituents.

Lastly, it must be noticed that certain substances used in the graphic arts-some of which possess in themselves a certain unctuousness-can be, as it were, rubbed into a suitably rough ened, and at the same time yielding, ground, to which they will adhere, though loosely, without binding material. This is the case with charcoal, chalks and pencil. The same property is imparted by a little gum or starch to soft coloured chalks, with which is executed the kind of work called "pastel." These are now also made up with an oleaginous medium and are known as " oil pastels." Pictures can be carried out in ordinary or in oil pastels, and the work should rank as a kind of painting. The coloured films, rubbed off from the sticks of soft chalk on a suitably rough and sometimes tinted paper, are artistic in their texture and capable of producing very beautiful effects of colour. Professor Church notes also that the colours laid on in this fashion seem peculiarly durable (Chemistry, p. 293).

32. The Processes of Painting: Preliminary Note.-These will be discussed from the point of view of the media employed, but certain departures from strict logical arrangement will be convenient. Thus, different processes of monumental painting on walls may be brought together though distinct media are employed. Tempera and early oil practice cannot be separated. Painting by the use of vitreous glazes fused by heat may be noticed first, as the process comes within the scope of the article, though it has generally been applied in a purely decorative spirit, so as to be a branch of the art of ornament rather than strictly speaking of painting (see § 2).

In painting processes proper fresco takes the lead. It is in its theory the simplest of all, and at the same time it has produced some of the most splendid results recorded in the annals of the art. With the fresco process may be grouped for the sake of convenience other methods of wall-painting, which share with it at any rate some of its characteristics.

One of these subsidiary methods of wall-painting is that known as the wax process or "encaustic," used in ancient times and revived in our own. Painting in wax, not specially on walls, was an important technique among the ancient Greeks, and the consideration of it introduces some difficult archaeological questions, at which space will not allow more than a glance. The wax used in the process, softened or melted by heat or driven by fire into the painting ground-whence the name "encaustic" or "burning in "-is really a tempera or binding material, and we are brought here to the important subject of tempera painting in general. It will have to be noticed in this connexion what were the chief binding materials used in the so-named

§ 33. Historical Use of the Various Processes of Painting.The extent and nature of the employment of these processes at different periods may have here a brief notice.

Tempera painting has had a far longer history and more extended use than any other. The Spaniard Pacheco, the father-in-law and teacher of Velazquez, remarks on the veneration due to tempera because it had its birthday with art itself, and was the process in which the famous ancient artists accomplished such marvels. In the matter of antiquity, painting with vitreous glazes is its only rival: glazed tiles formed, in fact, the chief polychrome decoration for the exteriors of the palaces of Mesopotamia, and were used also in Egypt; but all the wall-paintings in ancient Egypt and Babylonia and Mycenaean Greece, all the mummy cases and papyrus rolls in the first-named country are executed in tempera, and the same is true of the wall-paintings in Italian tombs. In Greece Proper paintings on terra-cotta fixed by fire were very common in the period before the Persian wars. When monumental wall-painting came to the front just after that event it was almost certainly in tempera rather than in fresco that Polygnotus and his companions executed their masterpieces. It has been doubted whether these artists painted directly on plaster or on wooden panels fixed to the wall, but the discovery in Greece of genuine mural paintings of the Mycenaean period has set these doubts at rest. In Italy tomb-paintings actually on plaster exist from the 6th century B.C. The earlier panel painters of the 5th and 4th centuries B.C. also used tempera processes, though their exact media are not recorded. About the time of Alexander there seems to have been felt a demand for a style of painting in which could be obtained greater depth and brilliancy of colouring, with corresponding force in relief, than was possible in the traditional tempera; and this led to painting in a wax medium with which abundance of “ "body" could be secured. There are many puzzling questions connected with this ancient encaustic, but the discovery in recent years of actual specimens of the work, in the form of portraits on the late Egyptian mummy cases of the first centuries A.D. have assisted the study. Meanwhile a new technique to have been in process of evolution for use on walls, for the fresco process, in a complete or modified form, was certainly in use among the Romans.

The history of the fresco process, as will presently be seen, is somewhat puzzling. Vitruvius and Pliny knew it, and it is mentioned in the Mount Athos Handbook, which incorporates the technical traditions of the art of the Eastern Empire; it appears also to have been in use in the Christian catacombs, but was not practised by the wall painters who adorned the early medieval churches south and north of the Alps. The difficulties of the process, and another reason to be noticed directly, may have led to its partial disuse in the West, but we find it again coming into vogue in Italy in the 13th and 14th centuries. In the early Christian centuries its place was taken in the monumental decoration of walls by marble inlays, and especially by glass mosaic, which is in itself an important form of wall-painting and may have put painting on plaster, and with it the fresco process, into the shade; notice will however presently be taken of a theory that seeks to establish a close technical connexion between mosaic work and the fresco painting, which, on the decline in the later medieval period of mosaic, came forward again into prominence.

The tempera processes were accordingly in vogue in early medieval times for wall-paintings (except to some extent in the East), for portable panels, and on parchment for the decoration and illustration of manuscripts. Meanwhile the

lively colours but also in relief; that is to say, each separate glaze brick had its surface, measuring about 12 in. by 9 in., modelled as well as painted for the exact place it had to occupy in the design. On these bricks there are formed small ridges in relief intended to keep the different liquid glazes apart before they were fixed by vitrifaction in the kiln. Chemical analysis has shown that the yellow colour is an antimoniat of lead, the white is oxide of tin, similar to the well-known opaque white glaze used by the Della Robbia in Italy, the blues and greens are probably oxides of copper, the red a sub-oxide of copper (Semper, Der Stil, i. 332). This same region of the world has remained through all time a great centre for the production of coloured glazed tiles, but the use of "Persian," "Moresque," and other decorated plaques has been more ornamental than pictorial."

$34. Painting with Coloured Vitreous Pastes.-There is no single work that deals with the whole subject of this material and its different uses in transparent or opaque form in the arts, but details will be found in the special articles where these uses are described. (See CERAMICS; MOSAIC; ENAMEL; GLASS, STAINED.) On the subject of the substances and processes employed in the colouring of the various vitreous pastes information will be found in H. H. Cunynghame's Art Enamelling on Metals (2nd ed., London, 1906, ch. vi.), but the subject is a large and highly technical one.

Coloured vitreous pastes are among the most valuable materials at the command of the decorative artists, and are employed in numerous techniques, as for example for the glazes of ceramic products including wall or floor tiles; for painted glass windows; for glass mosaic, and for all kinds of work in enamels. The vitreous paste is tinged in the mass with various metallic oxides, one of the finest colours being a ruby red obtained from gold. Silver gives yellow, copper a blue green, cobalt blue, chromium green, nickel brown, manganese violet, and so on. Tin in any form has the curious property of making the vitreous paste opaque. It should be understood that though the vitreous substance and the metallic oxides are essentially the same in all these processes, yet the preparation of the coloured pastes has to be specially conditioned in accordance with the particular technique in view. There are generally various ways of producing reds and blues and greens, &c., from oxides of different metals. The material is generally lustrous, and it admits of a great variety in colours, some of which are highly saturated and beautiful. It is on the lustre and colour of the substance, rather than on the pictorial designs that can be produced by its aid, that its artistic value depends; but though this implies that it comes under the heading Ornament rather than "Painting." yet in certain forms and at particular periods it has been the chief medium for the production of pictorial results, and must accordingly have here a brief notice.

The difference between opaque and transparent coloured glass is the basis of a division among the arts that employ the material. If it be kept transparent the finest possible effect is obtained in the stained-glass window, where the colours are seen by transmitted light. The stained-glass window came into general use in the early Gothic period, and was a substitute for the wall-paintings which had been common in the Romanesque churches of the 11th and 12th centuries. Hence it is a form, and a very sumptuous and beautiful form, of the art of mural painting, representing that art in the later medieval buildings north of the Alps. In Italy, where the practice of wall-painting continued without a break from early medieval to Renaissance times, the stained-glass window was not a national form of art.

The most effective use of opaque coloured vitreous pastes is in ceramics (pottery) and in glass mosaic. The terra-cotta plaque, or tile-painted with designs in glazes of the kind was, as we have seen (§ 7), one of the chief forms of exterior mural decoration in ancient Mesopotamia. The best existing examples were found not long ago on the site of the ancient Susa ("Shushan the palace of Scripture) and are now in the Louvre. Human

Glazed pottery only comes occasionally within the survey of the historian of painting. It does so in ancient Greece, because the earlier stages of the development of Greek painting can only be followed in this material; it does so, too, in a sense, in Italian faience and in some Oriental products, but these hardly fall within our view. The Greek vase was covered with a black glaze of extreme thinness and hardness, the composition of which is not known. Figure designs were painted in this on the natural clay of the vessel (see fig. 3, Plate IV.), or it was used for a background, the design being left the colour of the clay. Other colours, especially a red (oxide of iron) and white, were also employed to diversify the design and emphasize details, and these were also fixed by firing. A special kind of Greek vase was the so-called "polychrome lekuthos," a small upright vessel, the clay of which was covered with a white "slip "on which figure designs were painted in lively tints. The technique is not quite understood, but the colours were certainly fired. There is an article on " The Technical History of White Lecythi in the American Journal of Archaeology for 1907; the processes are not, however, analysed.

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In glass mosaic thin solid slabs of coloured vitreous pastes are broken up into little cubes of in. to in. in size and set in some suitable cement. The artist works from a coloured drawing and selects his cubes accordingly. Any number of shades of all hues can be obtained, and the modern mosaic workers of Italy boast that they dispose of some 25,000 different tints. As it is of the essence of the work to be simple and monumental in effect, a limited palette is all that is needed; and the mosaics recently executed in St Paul's in London are done in about thirty colours. The worker should have at hand appliances to cut to shape any particular cube wanted for a special detail.

The ancients used the art, and the finest existing ancient picture is in a mosaic, not indeed of glass pastes, but of coloured marbles. This is the famous "Battle of Issus" found at Pompeii. Glass mosaic came in under the early Roman Empire, but its chief use was in early Christian times, when it was the chief material for mural decoration of a pictorial kind. Ravenna is the place where this form of painting is most instructively represented, and the 5th and 6th centuries A.D. are the times of its greatest glory. At Rome and Constantinople there is fine early work, while that at Venice and Palermo is later. In the earliest and best examples the design is very simple, and a few monumental forms of epic dignity, against a flat background commonly of dark blue, represents the persons and scenes of the sacred narratives. The effect of colour is always sumptuous. Gold, especially for the backgrounds, is in later work freely employed.

The subject of enamel work forms the theme of a separate article. Here it need only be said that pictures can be produced by painting on a ground, generally of metal, with coloured vitreous pastes that are afterwards fixed by fusing. Limoges in France has been the great centre of the art, but enamelling loses in artistic value when a too exclusively pictorial result is aimed at.

§ 35. Fresco Painting.-Vitruvius (De Architectura, bk. vii. chs. 2, 3; age of Augustus), Mount Athos Handbook (Hermeneia, chs. 54 seq.; date uncertain but based on early tradition); Cennino

process? Furthermore, Berger holds the astonishing theory that on the self-coloured surfaces of Pompeian and Roman plastered walls the colour was not applied, as in the fresco process, to the surface of the final coat, but was mixed up with the actual material of the intonaco so that this was a coat of coloured plaster. This is of course a matter susceptible of ocular proof, but the actual fragments of ancient coloured stucco referred to by Berger afford a very slender support to the hypothesis, whereas everyone who, like the present writer, possesses such fragments can satisfy himself that in almost every case the colour coat is confined to the surface. The writer has a fragment of such stucco from Rome, coloured with vermilion, and here there is clear evidence that some substance has soaked into the plaster to the depth of an eighth of an inch, as would be the case in the "ganosis" of Vitruvius. The part thus affected is yellowish and harder than the rest of the plaster. A careful chemical analysis, kindly made for the purpose of this article by Principal Laurie of Edinburgh shows that, although the small quantity of the material available makes it impossible to attain certainty, yet the substance may possibly be wax with the slight admixture of some greasy substance. On the other hand all the writer's other specimens show the colour laid on to all appearance a fresco." The evidence of the coloured plaster in the house of about the 2nd century B.C. on Delos is wholly against Berger's view. The writer has many specimens of this, and they are all without exception coloured only on the surface. It is true that there are certain difficulties connected with Pompeian fresco practice, but the description of the process as a wet process in Vitruvius and Pliny is so absolutely unmistakable that Berger's theory must without hesitation be rejected.

The history of the fresco technique remains at the same time obscure. Here again Berger offers an interesting suggestion which cannot be passed over in silence. If the Pompeian technique, as he believes, be a wax process on dry plaster, followed by some form of tempera, how did the fresco technique, which is known both in East and West in the later medieval period, take its rise? The early medieval age was not a time when a difficult and monumental technique of the kind is likely to have been evolved, but Berger most ingeniously connects it with that of mosaic work. In mosaic the wall surface is at first rough plastered and a second and comparatively thin coat of cement is laid over it to receive and retain the cubes of coloured glass, only so much cement being laid each morning as the worker will cover with his tesserae before night. It was the practice sometimes to sketch in water-colours on the freshly laid patch of cement the design which was to be reproduced in mosaic, and Berger points to the incontestable fact if this sketch were allowed to remain without being covered with the cubes it would really be a painting in fresco. This is the way he thinks that the frescoe practice actually began, and the period would be that of the decline of mosaic work in the West as the middle ages advanced.

In spite of the attractiveness of these suggestions, we must reaffirm the view of this article that the testimony of Vitruvius is conclusive for the knowledge by the Romans of the early empire of the fresco technique. Why we do not find evidence of it far earlier cannot be determined, but it is worth noting that the success of the process depends on the plaster holding the moisture for a sufficient time, and this it can only do if it be pretty thick. In ancient Egypt and Mesopotamia, for example, the plaster used as painting ground was very thin, and especially in those hot climates would never have lent itself to fresco treatment. On the other side, the decline, and perhaps temporary extinction, of the technique in the early middle ages may be reasonably explained by the general condition of the arts after the break-up of the Roman Empire of the West. To return now to the technical questions from which this historical digression took its rise, it will be easily seen that the process of painting in fresco must be a rapid one, for it must be completed before the plaster has had time to dry. Hence only a certain portion of the work in hand is undertaken at a time, and only

so much of the final coat of plaster, called by the Italians intonaco is laid by the plasterer as will correspond to the amount the artist has laid out for himself in the time allowed him by the condition of the plaster. At the end of this time the plaster not painted on is cut away round the outline of the work already finished, and when operations are recommenced a fresh patch is laid on and joined up as neatly as possible to the old. In the making of these joints the ancient plasterer seems to have been more expert than the Italians of the Renaissance, and the seams are often pretty apparent in frescoes of the 15th and 16th centuries, so that they can be discerned in a good photograph. When they can be followed, they furnish information which it is often interesting to possess as to the amount that has been executed in a single day's work. Judging by this test, Mr Heath Wilson, in his Life of Michelangelo, computed that on the vault of the Sistine Michelangelo could paint a nude figure considerably above life size in two working days, the workmanship being perfect in every part. The colossal nude figures of young men on the cornice of the vault at most occupied four days each. The "Adam" (fig 34, Plate X.). was painted in four or perhaps in three. A day was generally occupied by the head of such figures, which were about 10 ft. high. Raphael, or rather his pupils, it is thus calculated, painted the Incendio del Borgo, containing about 350 sq. ft., in about forty days, the group of the young man carrying his father occupying three. The group of the Three Graces in the Villa Farnesina took five days at most. Luini, a most accomplished executant, could paint more than an entire figure, the size of life, in one day" (Second Report, p. 37). It has been noticed as one of the difficulties about the Pompeian frescoes, that joints hardly occur, or at any rate that larger surfaces of plaster were covered by the painter at a single time than was the case among Renaissance artists, and a conjectural explanation has been offered based on the fact that the ancient plaster ground, laid on in many successive coats while in each case the previous one was still humid, was thicker and would hold more moisture than the more modern intonaco, and would accordingly allow the artist longer time in which to carry out his work. Alberti, Armenini, and Palomino only contemplate one or two thin coats over the original rough cast, while Cornelius and his associates, who revived the process early in the 19th century, speak of an intonaco over the rough cast only about a quarter of an inch thick. A piece of plaster ground from Raphael's Loggie in the Vatican was found to be quite thin, and Donner calculated that the ancient grounds were on an average 3 in. thick, the modern only a little over 1 in. On such grounds work had necessarily to be finished within the day, and Cennino expressly says (ch. 67): "Consider how much you can paint in a day; for whatever you cover with plaster you must finish the same day." Hence almost invariably in Italian fresco practice every join means a new day's work. At Pompeii the plaster, it is thought, might have remained damp over night. In the Mount Athos Handbook tow was to be mixed with the plaster, undoubtedly to retard its drying.

This necessarily rapid execution gives to well-handled frescoes a simplicity and look of directness in technique that are of the essence of the aesthetic effect of this form of the art. Hence Vasari is right when he extols the process in the words, "of all the ways in which painters work, wall-painting is the finest and most masterly, since it consists in doing upon a single day that which in other methods may be accomplished in several by going over again what has been done.... there are many of our craft who do well enough in other kinds of work, as for example in oil or tempera, but fail in this, for this is in truth the most manly, the safest, and most solid of all ways of painting. Therefore let those who seek to work upon the wall, paint with a manly touch upon the fresh plaster, and avoid returning to it when it is dry" (Opere, ed. Milanesi, i. 181).

The process gives the artist another advantage in that his painting, being executed in the very material of the surface itself, seems essentially a part of the wall. It is lime painting on a lime ground, and fabric and enrichment are one. This