For real splendour of colour we must turn to glass mosaic, and for magnificent examples of its architectural use we cannot do better than look at the churches of Ravenna. My friend, the late J. T. Micklethwaite, speaking of mosaic, once humorously remarked that mosaic in decoration was "like beer—of no use unless you had a lot of it." (That is all very well for those who can imbibe, and the dictum should appeal to Britons.) However, the use of mosaic at Ravenna and St. Mark's shows what my friend meant. In the mausoleum of Gallia Placida, a small rounded arched and vaulted Byzantine building of the fifth century, there are no mouldings or carving, or any kind of architectural enrichment, to interfere with the effect of the complete lining of mosaic, chiefly in pale tones of gold and colour on a deep, subdued but rich blue ground. The effect is very solemn and splendid. The actual workmanship of the Ravenna mosaics would no doubt be considered rough by the more mechanical modern mosaicist who does not accept the cube principle in using tesserae. The head of the Empress Theodora at San Vitale, for instance, is very simply done. The tesserae are few—but since the effect from the proper distance is fine, they must be fit though few. Then these mosaics like all the ancient ones, must have been worked from the surface. This gives a certain play of surface and depth and richness of colour, each tesserae not having been set at precisely the same angle to the plane of the wall, or to its neighbour cube.
The modern Venetian way is to make the panels perfectly flat on the surface, the cement being spread over the tesserae when arranged face downwards. The modern Venetian workmen will copy a cartoon properly tesserated with the utmost precision, as I have discovered, but his panels have not the surface sparkle and variety of the old work. The method of putting in the tesserae from the front has however been revived since I made my designs. The design by Sir Edward Burne-Jones for the dome of the New American Church at Rome was worked in this way, and recently a mosaic altar-piece of "The Last Supper," for a church in Philadelphia, was executed in this way by Mr. and Mrs. Henry Holiday, the tesserae being inserted in a layer of putty.
In London we have the great work of Sir W. B. Richmond in the choir of St. Paul's, which was all worked from the surface—the tesserae being set in red lead putty which, occasionally allowed to show at the joints, gives a certain warmth of tone to the whole. Whatever difference of opinion there may be about the decoration of St. Paul's, the designs of Sir William Richmond are exceedingly fine and conceived in a noble spirit.
Mr. Anning Bell has carried out a charming design in mosaic worked from the surface for the exterior of the Horniman Museum. One projected for the exterior of the Whitechapel Picture Gallery, from a design of my own, has not so far been executed for want of funds.
I have often thought, when looking at the beautiful arrangements of tint in the fine shingle of some of our sea beaches, that the materials for a very effective kind of mosaic, at small cost, might be found there, and adapted for the ornamentation of the external walls of seaside houses, in friezes, strings, panels, or even entire walls. In thus reviving the ancient art of pebble-mosaic, a charming local character might thus be given to the buildings of certain of our coast places which would add very greatly to their attractions. The thing, of course, would need some intelligence and taste, without which indeed the most costly and beautiful materials in the world may be wasted.
One of the most charming and simple ways of decorating external walls is to be found in the patterns indented in the plaster of the surface filling of half-timbered houses such as are so plentiful in Suffolk and Essex. It is a characteristic and ancient method which it is gratifying to note is made use of by modern architects and builders in that district. Figures and ornament in relief are also used. A mixture of Portland cement and lime is a good material for this purpose, as it does not set too quickly, but finally sets hard and is durable.
Delicate plaster relief-work for ceilings and friezes is also a very charming method of interior decoration, and there are very fine examples scattered over the country, though its original home was, I presume, in Italy, whose craftsmen still maintain their pre-eminence in the skill with which they deal with the manipulation of all kinds of plaster-work. Plaster and stucco must have been largely used in ancient Rome, and there are very beautiful, both bold and delicate, examples in the decorations of the famous tombs of the Via Latina. In one instance, on a wagon vault, the figures appear to have been worked directly in the soft plaster and the relief-work is used with vigorous indented lines. The effect of the work is wonderfully direct, simple, and fresh, and suggests having been done with speed and certainty. Raphael, influenced no doubt by old Roman work, introduced modelled portions in his painted designs for the Loggia of the Vatican. The usual modern method is to model the design in clay, mould it in gelatine, and then cast it in fibrous plaster panels (supposing it is for relief work) and screw them in position, stopping the joints afterwards. This, though it has many conveniences, is not so artistic in its results as when the design is worked directly in stucco or gesso in its proper position; but if we could be sure of finding the plasterers and craftsman to do it, we should but rarely find the opportunity, or the client who would allow time for such work in situ.
A middle course is to model your design—say, for a frieze or ceiling—in gesso or stucco of some kind on fibrous plaster panels; and the design may be planned so as to cut up into convenient-sized panels to work on an easel in the studio, and be fixed in position afterwards.
I have worked panels in this way using plaster of paris, thin glue, and cotton wool. The ground should be wetted, or the suction stopped by a coat of shellac, or the work is apt to dry too quickly and peel off.
For delicate relief ornamentation, say, in wall panelling and furniture, a kind of gesso duro is good. This is a mixture of whitening, glue, boiled linseed oil and resin. It is mixed to a creamy consistency, the whitening being first soaked in water. The gesso is laid on with a brush—long pointed sable is best. The gesso sets slowly, but very hard, so that any part of the work could be scraped down if necessary.