What is Fresco?
Fundamentally, fresco is the art of painting water-suspended earth pigments onto a damp lime plaster wall. It is a unique approach in that as the painted plaster wall dries, it carbonizes to form a remarkably hard skin of calcium carbonate, locking the particles of absorbed pigment into place. Fresco becomes the wall. Thus, the methodology begins with the element crucial to fresco: lime.

The Lime Pit
Creation of the lime pit typically takes place before, or concurrent with, the artist’s formulation of preliminary compositional drawings, since lime should, ideally, break down for no less than two years before use as a prepared painting surface. A traditional lime pit consists of merely mixing powdered lime and water in a hole dug into the ground. Modern approaches usually involve lining the hole with a watertight tank, or series of tanks, to better control contamination and handling of the lime. Though care must be taken to guard against freezing temperatures, tanks also may be located above ground.

By the time the pit is filled and capped, many gallons of distilled water and quantities of the purest available lime will have been combined, small batches at a time, and poured into the pit to begin the breakdown of the mixture into a soft, gritty paste. The chemical breakdown of the lime crystals, called “slaking,” must continue until it is smooth enough to be used as plaster for the “skin,” or finished painting surface.

The Scratch Coat
In the meantime, many buckets of the partially-slaked lime will be combined with sand (two parts rough washed sand, one part lime) to create the “scratch coat,” a three-quarter-inch or more layer of foundation plaster troweled onto an existing interior wall. It is to this roughly-scored scratch coat that the final eighth-inch-thick skin is bound. The scratch coat, applied in two or three layers several months apart, may be reinforced by a membrane of metal mesh between the plaster and the wall. A typical Renaissance-era wall consisted of brick, which allowed the finished fresco to bind and dry with relative ease. Brick is not the common interior construction material it once was, so products like Densglass mounted on a reinforced masonry wall may serve today as a wallboard backing suitable for the scratch coat. Large-scale frescoes weighing thousands of pounds requires close consultation with the architect of the building.

Slaking
The process of mixing water with powdered lime is fraught with hazards. The combination produces a volatile chemical reaction, which creates enormous amounts of heat and steam. A fifty-pound bag of lime should be laid flat on the rim of a heat-resistant 55-gallon barrel containing 11-14 gallons of distilled water. Slitting the bag along its length, the mixer then dumps the bag’s contents into the water all at once and loosely covers the barrel with the empty bag to prevent splattering. Within a very short time, the mixture will begin roiling, bubbling and steaming, shaking the barrel with its vigorous action. Workers should wear protective clothing and a Plexiglas face shield to avoid the 400-degree spatters of wet lime and large volumes of steam escaping the mixing barrel. Despite these discomforts, the mixer must remain at the barrel using an industrial drill and extended paddle bit to ensure the batch is completely blended into a loose slush before it is poured into the pit. Once filled, the pit is then sealed in such a way as to minimize exposure to pollution and other contaminants. The pit should be checked regularly against water leaks and freezing. Additional distilled water can be periodically stirred into the mixture to maintain moisture content.

Composition
Fresco painting technique, because of the repeated cross-hatching of earth pigments onto the absorbent skin, resembles drawing as much as, or more than, painting. Long before approaching the wall, the artist begins with pencil, charcoal or conté drawings of models or other physical elements that will make up the overall preliminary compositional drawing. The compositional drawing is typically made on a one-inch to one-foot scale, though it has been suggested that using metric measurement greatly facilitates transference of gridded drawings to full scale. These initial drawings -- both individual sketch studies and the compositional drawing containing these elements -- require an artist with a keen instinctual eye for exactitude. Precision is critical when it comes time to enlarge the compositional drawing to full-scale size.

Studies
Once initial drawings are completed, the artist may create more fully refined drawings of certain elements – such as portraits – to fix them even more firmly in the mind. In theory, this “fixing-in-the-mind,” while appearing somewhat repetitive, is an important process throughout the course of conceptualization. It allows the artist to not only embed the subjects into memory, but to also discover new and serendipitous aspects of the original inspiration for the composition.

An oil color study of the full composition, generally the same size as the compositional drawing, should also be prepared. Color – rather than detail, as in the drawing – is emphasized. The artist’s knowledge of color, through experience in easel oil painting, comes heavily to bear. Here the artist more fully visualizes how color may affect composition, taking into account the “weight” of certain colors in balance with others. The color study may result in minor changes and realignments of all or part of the composition. The artist and colorist should then decide which color pigments must be acquired.

The Cartoon
In creating the “cartoons,” there is now a return to refined drawing: charcoal and conté drawings enlarged to the full scale of the finished fresco. The original compositional drawing, gridded with one-inch squares, is transferred to large sheets of paper with a one-foot grid pattern (again, a metric configuration may well be preferable). This is laborious and exacting, but results in the ability to view the full composition in terms of proportion and perspective. Relative weight and arrangement of individual elements in the picture can be confirmed as properly balanced and scaled to each other. The cartoons may also be mounted at the actual painting site wall to allow the artist line-of-sight references.

Tracing and Punching
More importantly, the cartoon is a primary gauge used to ensure that the accuracy of the original composition is maintained on the wall. To this end, semi-transparent tracing paper is laid over the cartoon and dominant lines are traced. The tracing paper is removed and punched with a large needle every few inches along the traced lines. These tracings are set aside for the sinopia process, and are used again when painting begins.

Site and Pigment Preparation
A short time prior to approaching the wall, scaffolding must be assembled as needed and grinding tables arranged at the work site. The artist or colorist supervises a team of assistants in preparing mixtures of pigments and distilled water, which will be rendered to a buttery texture by grinding the colors on glass plates with heavy stone or glass mullers. To whiten a color, slaked lime itself is often used. Mulling is labor intensive – even tedious – but necessary to ensure that pigments and lime crystals are ground finely enough to be drawn into the porous plaster as it dries.

It is at this point – with the colors prepared, the tracings and punchings completed, and a designated scratch coat area thoroughly misted with water the night before – that the artist and crew are ready to approach the wall.

Pouncing
The punched tracings, with the essential outline information from the cartoons, are affixed with string loops and suspended in place on the wall from nails gently driven into the scratch coat. Small gauze bags filled with red earth pigment are tapped – “pounced” – over the punched holes in the tracings to create a dotted outline on the scratch coat.

The Sinopia
The tracings are removed, and with drawings and cartoons mounted nearby for reference, the artist follows the dotted outline to begin the sinopia, or “underdrawing.” Though the scratch coat is rough and the drawing (using red pigment suspended in water) is not particularly detailed, it once again serves to fix the drawing in the mind and allows a final confirmation of compositional correctness. The scratch coat is then heavily misted with distilled water the night before painting.

The Intonaco
The muratore, or mason, is then brought in to apply the thin lime plaster skin over a portion of the sinopia designated by the artist. This application is referred to as the giornata, figuratively translated as “work that can be done in a day.” The muratore is generally directed to extend the fresh plaster lay an inch or so beyond the borders of the giornata to allow room for the artist to evenly trim the edges after the day’s work.

This, the final painting surface – called the intonaco – is an eighth-inch layer of fully slaked lime and sand, mixed one-to-one on-site. It must be neither too wet nor too dry for purposes of trowling and pigment absorbency. Moisture content is an inexact science even for experienced masons and fresco painters, and conditions at each site -- such as thickness and absorbency of the scratch coat, ambient room heat and humidity, temperature of the exterior of the wall -- must be accounted for. The intonaco must be troweled smooth and flat, and checked from various angles for irregularities. Spot applications of a watery mixture of pure lime can smooth irregularities in overall surface texture.

Assisting the Maestro
As the muratore’s work is being completed and a second pouncing onto the intonaco begins, assistants must prepare a table near the intonaco. This table becomes, in essence, the painter’s palette. On it rests containers – often bowls – of the ground colors selected for that day. These colors are suspended in distilled water, and must be frequently stirred or “spun” by an assistant to maintain suspension of the pigments. Also on the table are containers of various size brushes, a hand-held palette of mulled color, and several bowls of clean water for rinsing brushes. An assistant must stand at the ready to hand the painter brushes, damp sponges and maintain the containers of fresh water. If satisfied with the pouncing on the intonaco, the artist proceeds, guided by these critical reference points.

“Tearing it Out”
Mistakes cannot be brushed out or covered over, and therein lies the high challenge of fresco. Errors in laying the plaster, or even painting, may well result in having to scrape off all or part of the intonaco. Variances in color or inappropriate appearances of lime patches and the like can be corrected by creating a secondary painting surface of egg tempera one year after the fresco is painted. But even when taking correctly, the artist generally has a window of only several hours before the wall begins to “lock up,” becoming too dry to take pigment properly.

Misting
As the giornata nears completion, the artist may occasionally direct that the intonaco be sprayed with a fine mist of water, which acts as a medium to draw pigments further into the wall.

The End of the Day
At the end of each day, a “day line” must be cut, which consists of trimming the small amount of excess plaster left by the mason at the edge of the intonaco. The day line should be cut and beveled with fine, sharp and flexible instrument (a utility blade or trowel). Execution must be precise, as other giornatas will be troweled adjacent to all or part of the day line at some point. These new intonacos must be painstakingly “married” to the previous day line so as to render the borders virtually invisible.

The scratch coat well beyond the giornata is likely to have absorbed a great deal of moisture. Care must be taken not to over-water the scratch coat for the next day’s painting if the new intonaco is to be laid adjacent to the one prior to it.

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