OF STUCCO AND GESSO
Few things are more disheartening to the pursuer of plastic art than finding that, when he has carried his own labour to a certain point, he has to entrust it to another in order to render it permanent and useful. If he models in clay and wishes it burnt into terra cotta, the shrinkage and risk in firing, and the danger in transport to the kiln, are a nightmare to him. If he wishes it cast in plaster, the distortion by waste-moulding, or the cost of piece-moulding, are serious grievances to him, considering that after all he has but a friable result; and though this latter objection is minimised by Mrs. Laxton Clark's ingenious process of indurating plaster, yet I am persuaded that most modellers would prefer to complete their work in some permanent form with their own hands.
Having this desirable end in view, I wish to draw their attention to some disused processes which once largely prevailed, by which the artist is enabled to finish, and render durable and vendible, his work, without having to part with it or pay for another's aid.
These old processes are modelling in Stucco-duro and Gesso.
Stucco-duro, although of very ancient practice, is now practically a lost art. The materials required are simply well-burnt and slacked lime, a little fine sand, and some finely-ground unburnt lime-stone or white marble dust. These are well tempered together with water and beaten up with sticks until a good workable paste results. In fact, the preparation of the materials is exactly the same as that described by Vitruvius, who recommends that the fragments of marble be sifted into three degrees of fineness, using the coarser for the rough bossage, the medium for the general modelling, and the finest for the surface finish, after which it can be polished with chalk and powdered lime if necessary. Indeed, to so fine a surface can this material be brought, and so highly can it be polished, that he mentions its use for mirrors.
The only caution that it is needful to give is to avoid working too quickly; for, as Sir Henry Wooton, King James's ambassador at Venice, who greatly advocated the use of stucco-duro, observed, the stucco worker "makes his figures by addition and the carver by subtraction," and to avoid too great risk of the work cracking in drying, these additions must be made slowly where the relief is great. If the relief is very great, or if a figure of large dimensions is essayed, it may be needful even to delay the drying of the stucco, and the addition of a little stiff paste will insure this, so that the work may be consecutively worked upon for many days.
From the remains of the stucco work of classic times left us, we can realise how perfectly workable this material was; and if you examine the plaster casts taken from some most delicate low-relief plaques in stucco exhumed some ten years ago near the Villa Farnesina at Rome, or the rougher and readier fragments of stucco-duro itself from some Italo-Greek tombs, both of which are to be seen in the South Kensington Museum, you will at once be convinced of the great applicability of the process.
With the decadence of classic art some portion of the process seems to have been lost, and the use of pounded travertine was substituted for white marble; but, as the bassi-relievi of the early Renaissance were mostly decorated with colour, this was not important. The ground colours seem generally to have been laid on whilst the stucco was wet, as in fresco, and the details heightened with tempera or encaustic colours, sometimes with accessories enriched in gilt "gesso" (of which hereafter). Many remains of these exist, and in the Nineteenth Winter Exhibition of the Royal Academy there were no less than twelve very interesting examples of it exhibited, and in the South Kensington Museum are some few moderately good illustrations of it.
It was not, however, until the sixteenth century that the old means of producing the highly-finished white stucchi were rediscovered, and this revival of the art as an architectonic accessory is due to the exhumation of the baths of Titus under Leo X. Raphael and Giovanni da Udine were then so struck with the beauty of the stucco work thus exposed to view that its re-use was at once determined upon, and the Loggia of the Vatican was the first result of many experiments, though the re-invented process seems to have been precisely that described by Vitruvius. Naturally, the art of modelling in stucco at once became popular: the patronage of it by the Pope, and the practice of it by the artists who worked for him, gave it the highest sanction, and hardly a building of any architectural importance was erected in Italy during the sixteenth century that did not bear evidence of the artistic craft of the stuccatori.