© Amanda Quinby

In 1396 Cennino d’Andrea Cennini’s master died. Cennini was in the twelfth year of his apprenticeship with Agnolo Gaddi and though he would have liked to continue his studies under the renowned painter, the death of the master forced young Cennini to make his own way in the competitive world of early Renaissance Florentine art. He did, in fact, find work as an artist but apparently not enough to keep him too busy to also publish a handy treatise on his vocation. The sixteenth century painter, architect and art historian, Giorgio Vasari, while questioning Cennini’s skill as an artist (some of his work was still extant at the time) had nothing but praise for his instruction manual, Il Libro dell’ Arte. It is for this little “Craftsman’s Handbook” that Cennino Cennini is remembered today.

I mention Cennini because the continued relevance of his book is a testament to the basic nature of the craft of gilding. His methods influence both my work as a frame conservator and as a designer of new frames. Although writing for students of painting, Cennini specifically and systematically addresses the techniques and problems of gilders. Those problems, ranging from changes in the weather to inferior leaf, have not changed in six centuries. While I may no longer have to boil goats’ muzzles to make glue the essential materials and techniques required for gilding remain the same. Beyond his admonishments to practice one’s work carefully and diligently, Cennini offers practical advice for contemporary gilders. Over the next two months I will discuss the craft of gilding and some of the materials and methods used for both classical water gilding as well as its companion process; oil gilding. As a framer my bias is to work on wood picture moldings rather than the panels for painting with which Cennini was most concerned. Still, it is Il Libro dell’ Arte that I take as my point of departure.

Gesso is the essential base for most gilding. It obscures flaws, grain and pores in the surface to be gilded and provides the smooth, burnishable foundation required for most water gilding. Cennini will tell you how to make it from those goat muzzles or, more preferably, from goat and sheep parchment clippings. Those materials can still be had for the dedicated purist. I use rabbit skin glue which comes in sheets or granules and must be softened in water for severl hours and then gently melted over hot water. The warm glue is then mixed to a cream like consistency with whiting (finely ground chalk) to create gesso. Other additives such as glycerin, alcohol, and zinc white are sometimes recommended to get rid of air bubbles that cause pin holes or to improve sandability but basic gesso is simply glue and whiting.

Proportions of water to glue and glue to whiting vary according to the weather, the application of the gesso and the inclinations of the artist. More glue produces a stronger gesso which can be difficult to burnish. Too little glue may lead to a gesso not strong enough to hold to the surface on which it is painted or to withstand the rigors of the burnishing process.

Cennini recommends that, prior to gessoing, the wood first be coated with a layer of watered down glue. The purpose of the initial, weak application is that, “not being so strong it is just as if you were fasting, and ate a handful of sweetmeats, and drank a glass of good wine, which is an inducement for you to eat your dinner. So it is with this size: it is a means of giving the wood a taste for receiving the coats of size and gesso.” I find this to be true. Added to Cennini’s reasoning is my own belief that this weakened size also raises the grain of the wood thus giving extra tooth to the surface, an added incentive for the gesso to maintain its grip on the wood. Few things are more frustrating to the gilder than to have completed all but the burnishing only to find that the gesso cracks and flakes off under the pressure of the burnishing tool. More on that next month.

Once the multiple layers of gesso have been applied the task of smoothing the surface begins. Even the hardest gesso sands fairly easily and care must be taken not to remove too much and thus expose the wood.  I usually begin with 180 grit sand paper and work my way up to 400 grit. It is on this smoothed surface that burnished water gilding is most often done.

Texturing materials, such as sand, can also be added to gesso and applied in the final coat to some or all of a molding. I frequently sand the panels or coves of frames and there is a venerable tradition of stenciled designs applied using this method.

I believe that it is in the gesso that the craft of gilding most readily crosses into the realm of art. Design decisions are made at every step, from molding to leaf and finish choices but the opportunities for creativity and uniqueness are most broad at this stage of the frame making process. This was as true during Cennini’s time as it is today and it is with this appreciation of the practices of past craftsmen that conservation and restoration techniques can be better understood while our own contemporary design vocabulary is expanded.

All quotes in this article are taken from Daniel V. Thompson, Jr.’s translation of Il Libro dell’ Arte by Cenninio d’Andrea Cennini. New York: Dover Publications, Inc. 1954.