The Technique of Fresco Painting
Prepared for Roehampton Institute, Wimbleton, England Summer 1997

Materials:

For the plaster(s):

Lime: Must be high in calcium. “Quicklime” will give you the highest calcium content, but is very dangerous to handle. In the US, we use “high-calcium hydrated lime” (Quick lime, and slaked lime not available.) In Europe, good slaked lime is sold in plastic sacks and buckets. Its quality varies, and often needs to be sifted. There should be no less the 94% calcium, and no magnesium in the lime. Look for “type “S” Lime, or what is sometimes called,”miracle” lime. Avoid “dolomitic” lime: it is 30% magnesium, and unusable. Using dolomitic lime will result in a pitted surface, and possibly walls that fall apart.

Sand: Three (3) grades of clean, angular sand (or marble dust)
1. #16 - (rough) - for the first (or "scratch") coat
2. #18 - (medium) - for the "brown" coats
3. #30 - (fine) - for the intonaco (or painting) coat.
A note on Sand: It is important that the sand be river sand, sharp and angular, and free from salt and clay. If the sand is prewashed, it may be used “as is”, but if it has come from a river, or a yard where it has sat in a pile outdoors, it must be washed. Sand comes in different colors, all of which will change your painting base color. White marble dust will give you a very white, sparkle finish; browner sand will tone down your finish some. During the Renaissance, many artists used volcanic sand, which left a slightly blue-gray surface. .

Portland Cement: Pure white. (In the US: difficult to find, so locate a sourse as early as possible)

For a portable, constructed panel:

Exterior Plywood: 1/2 inch (for under 2’ X 2”) ; 3/4 inch for larger panels
2 inch wooden strips: for the edge of the panel, to create raised borders, and hold in the plaster
Expanded metal lath: Any metal used must be galvanized to prevent rust. Cut to the size of the panel
Building paper: Water proof “tar Paper”.
Galvanized staples

For a simpler, ready to use panel, not larger than 12 inches by 16 inches
Gypsum “dry wall”: not larger than 12 inches by 16 inches. ( also called “wall board” and “sheet rock”)
Plasterweld: resinous emulsion, a bonding agent, used for bonding plaster to concrete or cement surfaces

For construction of the portable panels: tin snips for cutting the metal lathe utility knife (razor blade) saw / hammer / nails

Tools for plastering: 

4-1/2 x 11 in. plasterer's trowel 5-in. pointed or square hand trowel wood float cork float a trough for mixing plaster. a hoe, for mixing plaster large, stiff brush 3-4 inches wide hose, with spray nozzle a few 5 gallon buckets cloth work gloves rubber work gloves a spray bottle filled with waste

Preparation of the Lime:

Once you have the lime you must slake it - that is, put it into water. High Calcium lime is caustic and dangerous: wear a dust mask or respirator, cover the eyes with work goggles, and have no exposed skin. You will need a plastic container with a lid, a new, (clean garbage container works well. If your lime will sit for a long time in one place use a large (50 gallon) plastic trash container, but remember that the lime may have to be transported in the future to a worksite. You may use smaller, five gallon buckets, which are easily obtained, and transported.) In either case, fill the bucket about 2/3 with water and sift the lime through your fingers into it, until it “peaks,” that is, until enough lime has been added so that the water will dissolve no more. For a 50 gallon bucket, you will need 120 (3 1/2 sacks) pounds. For a 5 gallon bucket, you will use about 12 pounds of dry, hydrated Lime. Cap it, and put it aside - somewhere where it won't freeze - for three months. When preparation time is short, the Lime putty can be used in three weeks, but the longer it soaks, the better. Medieval frescoes were often made with lime slaked for many years. This lengthy slaking is done to prevent cracking; the longer lime slakes, the more elastic it becomes. In Europe, already slaked lime putty can be purchased.

Plaster is applied in 5 or more coats to a combined thickness of 3/4 to 7/8 inches (medieval frescos were often as thick as 2 inches. This many coats are applied for 4 reasons: (1) to give strength: the longer the plaster takes to dry, the longer it hydrates, and the harder it will be. (2) to prevent cracking. (3) to extend the painting time of the final coat. (4) to make the final carbonate layer that holds the pigment stronger.

Preparation of the portable panels:

Plywood, constructed panel: Cut the plywood to the desired size. Staple the tar paper to the plywood panel. Nail the 2 inch X 2 inch wooden strips to the surface of the panel, over the paper. It should make a perfect, raised border/frame to hold the plaster. Cut the metal lathe to fit into the framed in area of the panel & staple it onto the wood, through the paper every 6 inches.

Wall board panel: Cut to desired size, coat with one layer of Plasterweld, just before the 1st coat of plaster is applied.

Plastering:

1st coat ( italian: trullisatio / english: “scratch coat”): The 1st coat is trowelled onto the metal lathe, (or directly onto the still tacky Plasterweld, if you are using wall board.) This caot is applied to the wall, if the fresco is to be executed on the wall. It consists of:

1-1/2 parts mixture of #16 and #18 sand (or marble dust) 1 part pure white Portland Cement 1 part lime putty (slaked lime)

The ingredients are put into a trough, and mixed by hand with first the hoe, then mixed and beaten with the plaster’s trowel. At L’ecole de Beaux Art, in Paris, we “grated” the mixture 7 times: Place the trough on the floor, standing over it, with your feet to either side. Pile the mix in one end of the trough, and grate the mixture, pushing it under the trowel in small amounts, until it collects in the other end of the trough( the end between your ankles.) The cement will cause this mix to harden, so don't mix up any more than you can use in a short time.

Plastering is a learned craft, and difficult to explain without physical demonstration. The angle at which the trowel is held is most important, too steep and you will draw the plaster, too flat and the trowel will stick and pull the plaster up. Use the largest trowel for most of the plastering, the smaller will help around the edges. Plaster must be applied in long even strokes, smoothing as you go. Start at the bottom and work up. A firm hand is needed as plaster should be applied with as much pressure as possible. Each coat must be worked in all directions to insure against cracking. All this may sound vague, but after you have had some practice it will make sense. The first coat should be thoroughly scratched; Use a small piece of the metal lathe as a comb and scratch in all direction. This should be given a few days to a week fully cure. You may mix the plaster for the next coats at this time;

The next 2 coats consist of:
2 parts #18 (medium) sand or marble dust 1 part lime putty.

This mixture will not set up unless exposed to air, so mix up enough for all three coats and store in a bucket with a little water floating on top, covered to keep out dirt and dust.

2nd coat (Italian: “arriccio” / french: “crepi” / english: “browncoat”): The first coat must be wet down before the application of the second. A plastic squeeze bottle, or a large, stiff brush can be used. For large work, use a hose with a spray nozzle. Stand the panel on end and start at the top, letting the water soak down. You want the surface wet but with no standing water. The second coat is applied in the same manner as the first - worked in all directions - to a thickness of about 1/8-in., and "floated." Floating is done by first wetting the wood float, then placing it flat against the surface, working in a circular motion, with light pressure, over the entire surface. Let the float do the work. It will smooth the high spots and make low spots evident. Work at the surface, taking plaster from the high spots and adding it to the low spots, until it's a smooth, flat plane. If there are holes in the surface, after the plaster has been applied, you may form a little ball of the mortar, and throw it into the hole, smoothing or “floating” it with the float. This must also sit a few days to cure.

3rd coat (italian: “arenato” / english: “sand coat”): The second coat must be wet down before the application of the third. The 3rd coat is applied, worked, and floated in the same manner as the second, and allowed to cure. The sinopia, the full-scale drawing is applied onto this surface, drawn on over the rough plaster of entire wall, corrected for perspective and other errors, all in red ocher pigment and water. The sinopia is then used for tracings of the work to be done each day. Because painting may only continue as long as the plaster is still wet, each "days work" (giornata) consists of the size area the artist can paint in about an eight hour period.

4th /5th coat (italian: “intonico” / french: “enduit”/ english: painting coat): The 4th and 5th coat are, essentially 1 coat put on in steps. In the trough, mix /beat /grate: 1 part #30 sand or marble dust, 1 part lime putty.

The final two coats are applied over just the area to be painted that day. Seams between one day‘s work and another are planned to fall along a line in e the composition, and must be kept very simple.

The 3rd coat must be wet down before the application of the fourth coat. The 4th coat is applied, worked, and floated in the same manner as the third, but is applied in a thin layer. It is actually a “skim coat” for the 5th layer. This must be left alone after application, 15 minutes to an hour (depending on conditions) until set. The 5th and final coat is applied as thinly as possible as it is only for smoothing the surface. Care should be taken to keep the trowel clean so as not to deposit any large aggregate or foreign matter into the intonaco, wipe the trowel off in between swipes. It should not be worked too much, smooth as you go. Use a side light to locate and remove all streaks and low spots. No floating is done to the intonaco, rather it is polished. In order to polish the surface properly, it is necessary to file the 4-1/2-in. end of your large trowel to a rounded edge. Place a portable light to the side of the surface, aiming so that it “rakes” across the surface. This will illuminate and irregularities and holes which must be filled in and finished. Once the surface is set, gently, using a tap and draw motion, beat the surface with this round edge. This will bring up the flat side of the angular aggregate and draw the lime up around it. A very hard, flat, and smooth surface may be obtained in this manner.

To test the surface for painting readiness, a brush dipped in water may be stroked across it. If the water is directly absorbed, the surface is ready. If it lays on top, you must wait. When the surface is ready, the tracing of the cartoon (see below) is laid on top, correctly lined up, and very lightly pounced with a small cloth bag filled with brown or red ochre pigment. This transfers the drawing onto the finish surface with neat, dotted lines. For panels small enough to be painted in one sitting, a full-size cartoon will be enough, as it may be perforated for final transfer, omitting the sinopia altogether. If you prefer, the drawing maybe gently incised into the plaster by drawing over the cartoon lines with a pointed, blunt tool, in which case you dispense altogether with the perforations and pouncing. A side “raking” light is essential for this method; both ways of transferring are visible in most wall-sized frescoes.

Note on the various recipes for fresco:
The various fresco recipes given may look very different, and rather confusing to reconcile, and indeed, they may be. However, the different approaches may be looked at as being essentially similar in their broad outlines. Each has a Scratch Coat: this layer, which may or may not contain cement is, by definition, very rough(scratched) Its purpose is twofold: it must be firmly anchored to the underlying wall. 2. It must be rough enough to hold the following layer. Think of the scratches as burrs which will extend up into the next layer, anchoring it to the scratch coat. The next layer of plaster may be thought of as the “intermediate, or stabilizing” layer. It may consist of 1 or several coats, and may include both the arriciato and the arenato. Its purpose is threefold: it holds onto the scratch coat. It provides tooth for the final painting coat, and, by virtue of its thickness, it is a major component in determining how long the intonaco, or painting coat will take to dry. The final, painting coat, or “intonaco” is just that: the painting surface. it may consist of 12 or a few layers, usually all put on prior to painting.

Cartoon Drawings are done to scale ; a full-sized cartoon is be made before the 4th/5th coat is applied. It is fully detailed, and in color, if possible. All details are worked out ahead of time, for 2 reasons: 1. the painting is done only while the plaster is fresh, usually that means one day only. 2. Fresco is essentially a transparent medium. Everything shows through in the finished painting. It is recommended that the beginning fresco student make a replica of an existing fresco (Byzantine, for the icon painter, Roman or Renaissance for the secular painter.) This will allow the student to concentrate on the techniques, which are new, and sometimes very difficult, without worrying too much about drawing and painting. It is imperative to have your cartoon and colors prepared before the final coats of plaster are applied, because the plaster will be drying - and time spent doing something else is lost painting time.

Tracing An exact tracing is made of the cartoon, and perforated with holes, using a pin or a dressmaker’s needle-wheel. It is left in one piece, if the fresco is to be done in one day. If the fresco is to be done in 2 or more pieces, the tracing is cut into those pieces.

Pigments There are many fresco pallets, from various times and places. a simple, basic palette, easily obtained:
Vine black or spinel black or ivory black titanium white yellow ochre red ochre brown ochre raw sienna burnt sienna puzzuoli red venetian red almagre morodo cobalt blue cobalt-cerulean blue viridian green yellow oxide red oxide cadmium red

Grinding the colors tools: a large rectangular piece of plate glass: 24 X 30, or larger a 3 inch wide glass mueller or piece of granite that is polished on the bottom, and fits into the palm of the hand small jars, glass or plastic, to hold the colors large, flexible palette knife distilled water carburndum, for surfacing the glass and mueller

Pigments must be ground in distilled water to a state of suspension - that is, until each particle is completely surrounded by, or suspended in, water. This takes about 20 minutes for the softer ones and up to an hour forth harder ones. For grinding, I use a four-pound glass mueller and a piece of glass, about 18-24 in., square. Place the mueller over the pigment and work in a circular motion. Every so often draw the pigment back to the center with a palette knife and start again. Water may be added as needed;you will find a point where the mueller just floats over the pigment, this is the correct wetness. To test for suspension keep a small jar of water on the side and touch a small amount of color to the surface; if it floats, it's ready. Care should be taken to make sure the colors are kept clean. If they are kept wet they may be stored in jars indefinitely for later use. If they dry out, they must be reground. An alternative grinding method: obtain a spinning stone tumbler, used for grinding stones to a smooth surface. Using a jar that fits into the spinner, fill it 1/3 full with pigment, and distilled water to fill the jar to 2/3 full. add 5 to 7 ceramic marbles (used for mixing ceramic glazes, and obtained at a shop that sell ceramics supplies.) Let the pigment spin overnight, remove the ceramic balls, and let the pigment settle, which may take some days, depending on which pigment being ground, and pour off the extra water. The pigment can be left in the jar, or stored in another container. Small jars are best. They should be sterilized in boiling water. Several colors can be ground at once, if the tumbler can accommodate the jars.

SELECTED LIST OF WORKS CONSULTED

Cunningham, Lawrence S., and John J. Reich, Culture and values: a survey of Western humanities, 2nd ed. New York, Holt, Rinehart & Winston, 1990. 2 vols.; see vol. 1.

Dimitroff, Stephen Pope, Apprentice to Diego Rivera in Detroit and fresco workshops manual, Stephen Pope Dimitroff, 1986.

Mora, Paolo, et al, Conservation of wall paintings, Glasgow, Butterworths, 1984.

Nodmark, Ollie: Fresco Painting American Arists Group, inc. New York 1947

Arts Foundation of Michigan Web Page (World Wide Web) 645 Griswold St., Suite 2164 Detroit, MI 48226 Kimberly Adams, Executive Director - afmadams@tmn.com