Fresco-buono, or true fresco, is so called because the painting is executed “a fresco,” that is, directly on the fresh, or wet plaster, which forms the painting surface of the wall. This plaster, or mortar, is a mixture of lime and sand, and the colours used in the painting are such as will remain unchanged in hue when in contact or in mixture with the lime. When all necessary details relating to the method of procedure connected with the work are carefully carried out, true fresco paintings may be said to have a higher degree of permanence and durability than those executed by any other method or medium. The fine surface texture and luminous quality of buon fresco pre-eminently distinguishes it as the most beautiful colour finish for mural decoration.

The great permanence of fresco paintings is due to the formation of carbonates, and sometimes silicates, of lime on the surface of the plaster, which takes place during the drying of the latter. The carbonic acid contained in the natural limestone is driven out of it by the process of burning in the kiln, and after the burnt lime has been slaked into lime “putty,” it has then become what is known as a hydrate of lime. As long as the plaster is wet on the wall the lime in the plaster exists in the state of a hydrate, and the applied colours of the painting become saturated with this form of lime; but during the process of drying, the lime on the surface, and to a slight depth below the surface of the plaster, rapidly absorbs carbonic acid gas from the atmosphere, and becomes a carbonate of lime, which is formed as a hard and crystalline skin, or surface covering, under which the colours are locked up, and so protected from any atmospheric influences. In addition to this carbonate surface a silicate of lime is sometimes formed, especially when in the painting some of the more earthy colours are used which may have silica in their composition. These thin coverings of carbonates and silicates of lime render fresco paintings impervious to wet or damp on the surface, so that they may be occasionally washed without injury; but bad air, such as sulphuretted hydrogen gases, or the sulphur products given off by gas and coal combustion, will in time convert the carbonate covering into a sulphate of lime, a substance which disintegrates and destroys, not only the colours, but the plaster surface also. This would suggest that in buildings which contain fresco paintings coal fires and gas should not be used for heating and lighting purposes, and also that the buildings should be properly ventilated.

Preparation of the Wall in Buon-Fresco:

The wall on which a work in buon-fresco is to be painted should be of good brick, or if a stone wall, it should be lined with brick on its inner face, or, better still, it should be what is known as a hollow brick wall—that is, one having an air-space between the outer and inner linings. The joints between the bricks should be scored out, so as to leave a key for the first coating of rough plaster; this should consist of old lime and coarse, gritty, well-washed river sand, mixed with ox-hair, or white asbestos cut into small bits, so as to bind the mixture more effectually. For this first coating of plaster the usual proportions are one part of lime and two parts of the gritty sand; it should be about three-quarters of an inch in thickness. This coating should have a roughened surface, made by scratching it with a coarse-toothed kind of wooden comb, and should be left for the best part of a year, so that it may thoroughly harden, before it receives the second, and last, coat of plaster, that on which the painting is to be executed, which is known as the intonaco. This plaster mixture must be prepared with great care, and more than sufficient to cover the whole wall space should be made before beginning the painting, so as to get the whole surface evenly tempered, and of the same mixture; for if different mixtures were made, and at different times, the lime and sand might vary in proportions, which would possibly affect the colours of the painting, and prevent them drying uniformly, as to tint or tone.

The proportions of lime and sand for the intonaco is, one part of lime and three parts of fine and well-washed river sand. Pit sand must not be used, on account of the clay and earthy matter which it contains; nor sea sand, which of course contains a certain amount of salt that would attract damp and cause the lime to perish. The lime must be well slaked, and must be fairly old in the “putty” state, so that there may be no fear of its blistering and blowing off here and there in round flakes on the finished surface, which it will do if it is too new or not properly slaked, even six or eight months after the plaster has been spread on the wall.

The method of preparing lime for fresco work is, first to select the best white variety which has been properly calcined. The lime is put into a large wooden trough with sufficient clean water to slake and dissolve it into a thin creamy consistency. The mixture is then strained through a fine sieve into a brick-lined pit, roofed over to keep out the wet and dust. A thick coating of clean river sand should be put over the lime when it has cooled down and thickened into a paste, and has become what is known as “lime putty.”

There are many tales and legends concerning the extreme old age of lime putty before it has been used in the plaster of wall surfaces, or as a painting material in fresco.

It has been stated that for some of the Italian frescos the lime used was eighty years old. As a matter of fact it is quite ripe for use about one year after it has been slaked. The lime used by Sir Edward J. Poynter in his fresco in St. Stephen’s Church at Dulwich was about two years old, and that used in the Houses of Parliament frescos was three years. The quality of the lime, however, is of more consequence than its age. The common grey lime used by the London builders should be avoided; the best English variety is the pure white limestone, which is quarried and burnt near Buxton in Derbyshire.

Before describing the method of laying on the last plaster ground, or intonaco, a few words must be said about the preparation of the design or subject to be painted. A finished coloured drawing or painting of the design, to a smaller, or even to the same scale as the fresco painting, must be prepared, and the artist should endeavour to make an exact copy of this on the plaster surface, as there is no time to experiment in colour schemes, or to make alterations from the original coloured design in the short period that is at the disposal of the painter when he is at work on the wet plaster. If the colour sketch of the work is prepared on a small scale it will be also necessary that a cartoon in light and shade drawing should be made to the full scale of the fresco painting, before beginning to paint on the wall.

As the colours, and everything else that may be required, must be in readiness, and close at hand before laying on the plaster ground and before commencing the painting, it will be as well to indicate here the proper colours which may be safely used on the lime plaster.

Although the palette in buon-fresco painting is very simple and restricted as to the number of the colours which may be trusted to withstand the caustic action of the lime, at the same time a fairly rich and luminous colour scheme may be obtained, notwithstanding the limited range of the palette. The following list may be safely relied upon:—

There are other pigments that might be used, but are really not necessary, and some of them are doubtful as to their permanence. One colour, not in our list, is the genuine ultramarine, a splendid blue, and thoroughly permanent in buon-fresco, but its great price prohibits its use, except in very small quantities, or on small portions of the work. French, or factitious, ultramarine is also very permanent, and withstands the action of the lime, but at the same time it is a most harsh and disagreeable colour when used in lime or in any other kind of fresco; when used alone it destroys by its intensity of hue the proper values of other colours in the scheme; on the other hand, if any attempt is made to tone it down by mixing it with another pigment, or by glazing another colour over it, the result is cold and muddy in the extreme, so it is best left out of the list, as it is almost unmanageable in fresco. Vermilion is rendered durable in fresco by pouring lime-water over the powdered colour, and then draining this water off, without disturbing the colour. This washing is repeated four or five times, before the vermilion is ready for use. Permanent white, which is a barium sulphate, and tin white, or tin binoxide, may both be used in lime frescoes, but they are unnecessary, and not so good for the purpose as lime white. Lemon yellow, Naples yellow, aureolin, Venetian red, and terre-verte may be used with lime, but it all depends on the manufacture of these colours as to whether or not they may be used with safety. For example, the Naples yellow, Venetian red, and terre-verte pigments of to-day are quite different in their chemical constituents to the same named colours of the fourteenth and fifteenth centuries. Yellow ochre, though it has been used very much by the old Italian frescanti, is not to be depended upon when used in lime fresco in this country, as it consists of a mixture or combination of hydrate of iron and clay; it therefore attracts the damp that is nearly always present in our atmosphere. Of course, it can be safely used in very dry climates, but it may be mentioned that it has been one of the pigments which has largely perished in some of the frescos of the Houses of Parliament. Another objection to its use in fresco is, that the caustic nature of the lime is apt to change yellow ochre to a light red, an after effect which may not be altogether desirable. Raw sienna, however, more than takes the place of yellow ochre, and is one of the most useful colours in fresco painting. We should say that the three most permanent and beautiful colours for use on the lime plaster are raw sienna, burnt umber, and Indian red, and whether used in transparent washes or in solid tints, as when mixed with lime-white, or in the full strength of their hues, they always dry out luminous and brilliant. All the colours should be ground very finely in water, and kept in covered jars or wide-mouthed glass bottles. The lime-white should be strained through muslin and kept covered. A bone or ivory palette knife must be used, and the palette should be made of tinned metal, having a series of small circular wells to hold the various colours. Brushes are of the ordinary kind, hog-hair, and a few long sable riggers. Hog-hair brushes are best for use when they are of a flat shape, but of a roundish finish at the end, like an old or half-worn brush, so that when in use they will not disturb the surface of the wet plaster, which a new or square-ended brush is apt to do.

When everything is in readiness to commence work, a portion of the rough wall surface should be thoroughly saturated with water, and the plaster ground, or intonaco, should be laid on with a wooden trowel, beginning at the top and at an angle of the wall, and large enough in area to constitute a day’s work, or, rather, as much as can be done in about five hours; for after that time it is not safe to work on the new plaster, as it then becomes too dry: if allowed to get in this condition the colours will not properly incorporate with the body of the plaster, for if any painting is done when the plaster is in a half-dry state the colours will not adhere permanently to the wall, but will scale off the surface, or may be brushed off loosely when dry. When any portion of the plaster ground becomes too dry to work upon.

it must be cut right away and a new coating of plaster applied; it is of no avail to syringe it with water in order to keep it damp for painting on, as the water only weakens the nature of the lime in the plaster. The chemical action between the atmosphere and the lime, necessary for the firm locking up of the colours, will have taken place after four or five hours’ time, according to condition of the atmosphere; and this action will not repeat itself or be brought about by any application of water after the period named.

When the day’s work is finished, any part of the surface not painted on must be cut away, and the plaster all around the edge must be under-cut, the cut sloping well inwards, so as to form a key for the new piece of plaster for the next day’s work. This coating of plaster should be rather more than half-an-inch in thickness, and should be finished to a level, but not too smooth, a surface, with the wooden trowel, or “float.” An iron trowel must not be used. After the plaster is laid on it should remain about ten minutes or so before painting, so as to allow it to set. It should then be coated with a tint, that would be a deep vellum colour when dry, made of a mixture of lime-white and a little raw sienna, about the thickness of cream; this will give a slightly smoother surface to the plaster and will act as a luminous ground for the subsequent colouring, besides acting a very important part as an under-coating on which the superimposed colours will “bear out” more effectively. The water used should be distilled or boiled, or rain water collected in clean vessels, as hard water generally contains a quantity of chalk, and for this reason it is not so powerful a solvent of the lime as soft or distilled water.

The portion of the design selected for the day’s painting is traced from the cartoon, and is transferred to the soft plaster through the holes, which are pricked through the tracing paper, by means of pouncing with powdered charcoal contained in a muslin bag, or it may have the outline traced through with a sharp-pointed wooden stile; this will leave a slightly depressed line on the soft plaster, and is a cleaner method than the charcoal pounce, and on the whole the more preferable one.

We have now arrived at the stage of the work when the painting may be proceeded with. It may be here mentioned that, in order to try the hues of the colours and various tints, an ordinary brick having a thick coating of plaster of Paris, that has been allowed to become thoroughly dry, should be at hand. If a touch from the brush, dipped in any tint, be put on this plastered brick it will dry immediately, and show at once the actual shade of colour that such a tint will be when, after some days, it has dried out on the plaster surface. It generally takes three or four days, according to the season of the year, or heat of the room, before the wall surface and the applied colours finally dry out, and all

colours, more particularly the lighter tints and half-tones, dry eventually ever so much lighter than they appear when first laid on. It is only the very darkest tones, or pigments used in their full strength, those that have no lime mixed with them, that dry anything near the full strength of their wet state, and then there are exceptions to this; so it follows that in buon-fresco painting the artist must paint in a much darker key than the work is intended to appear when it has dried out.

As regards the method of execution in painting it may be urged that the artist will work according to his own feeling or temperament: for example, some may decide to paint in thin transparent washes or glazings, as in water-colour painting; others may prefer to use the colours in a thick impasto method, as in oil painting. Either method may be adopted with success, but we should say that a judicious mixture of both methods, in the same work, will obtain the clearest and most luminous results, for, as a matter of technique, fresco lends itself admirably to either methods of painting. The general rule is to model the shades, half-tones and lights, broadly at first and in the order named, with brushes rather large than small, and then to finish off by strengthening the shadows with lesser touches, or by a series of delicately hatched lines, and brightening the lights in the same way, using for these purposes sable rigger brushes. The reason for this is that every touch tells, especially when using a sable brush; you cannot press or lean on your brush on the soft plaster without disturbing the underneath colours, and possibly destroying the surface of the plaster as well. It will be seen from this that the fresco painter must cultivate a light hand for his work; he cannot indulge, for instance, in that dexterity of handling that may be accomplished in oil or in, say, spirit-fresco painting, simply because of the danger of working up the soft and wet plaster ground: he must know what he has to do, and must do it frankly and at once; for, although to a certain extent the artist may be able to paint over parts and so correct occasional mistakes, it is not advisable to do so, as the corrections will more or less show when the work has dried out, by looking muddy, and consequently less luminous than they ought to be. The only alternative, when a correction is necessary, is to cut the piece out, and lay on a fresh plaster ground. All this shows how important it is to have a full-sized cartoon in light and shade, and also a colour scheme previously prepared, from which the fresco painting may be almost copied directly on to the wet plaster.