[Laboratories, Pigments and Binders]

Fresco Preparation

In Italian, fresco means 'fresh'. This painting technique was developed into a fine art during the Italian Renaissance (15th and 16th centuries). The fresco painting is a highly durable art form, as exemplified by the many surviving frescoes such as Michelangelo's Cistine Chapel Ceiling. These frescoes have lasted 500 years, wheras we do not expect our cement to last longer than 20 years.

The frescoes we make will be creasted in layers. These are the steps we will use to create a bona fide fresco. Carolyn Fitz of KAMSC (Kalamazoo (MI) Area Math and Science Center) with the help of Western Michigan University MFA student Kristin Casaletto prepared these instructions and used them in the spring of 1998. In the spring of 1999 they were used for the Chemistry and Art course taught at the Lee Honors College of Western Michigan University.

Some details about the chemistry of calcium and of frescoes follow these steps.

1. A 9" by 12" plywood panel topped with stapled metal lath and framed.

2. The trusilar, or scratch coat, is applied to a depth about half the height of frame. This layer is made by mixing coarse sand and slaked lime in a 2:1 proportion in a dish pan while wearing gloves. The mixture is pressed into the metal lath using hands and a diamond trowel…

…and smoothed.

This layer is scored with a cross-hatch pattern and then allowed to dry. The drying process should take place in a room that is not too dry or to warm. Slow drying is best and should take about one week. When the surface no longer feels cool to the touch it is dry. It is apparently an endothermic process!.

3. Arricio, the second layer, is made of medium grain sand and slaked lime in a 2:1 proportion. The dry first layer is brushed or sprayed with water,

And then the second layer is applied to about the same depth as the first layer.

The same smoothing techniques are used as with the trusilar.

Picture to be placed here.

4. Intonaco, the final layer, is of very fine texture. It is made from fine white sand and slaked lime in a 1:1 proportion. It is applied to the arricio when grains of plaster from the arricio layer will no longer adhere to the back side of your fingers when lightly pressed against its surface.

The intonaco is a very thin layer.

It provides a smooth sruface on which to apply the pigment.

5. A cartoon must be prepared.

Holes are punched. A dissecting needle with a protective piece of cardboard or other substance under the paper works well.

6. The cartoon will be pounced when the plaster surface demonstrates the capacity to absorb water. Dip a clean water color brush in distilled water, and then dab some water on the surface. If the water is drawn in, it is time to pounce the cartoon.

Picture to be placed here.

Place the cartoon on the moist, but absorbent surface. It may help to tape down the cartoon. Using a cotton swab dipped in dry pigment, dab gently on the holes of the cartoon, …

… transferring an outline of your desired image to the surface.

7. Dry pigments…
…must be mixed with water…
…and then ground on a glass sheet with a muller.

Water and pigment are added to give a good consistency.

A scraper is used to direct the spreading pigment surface back into the center area of the glass.

8. The prepared pigments must be diluted with distilled water. The consistency is at the descretion of the artist. Pastel shades may be achieved by mixing slaked lime with brighter colors.

9. The painted fresco should be allowed to dry in one place for several weeks to cure - slowly. During the curing time, carbon dioxide gas is absorbed into the surface of the fresco, converting the slaked lime into calcium carbonate.

Pic to be placed here.

Calcium and the Chemistry of Frescoes,

by Autumn Borchak at the Lee Honors College of Western Michigan University during the spring of 1999.

Calcium is a metallic element, fifth in abundance in the earthís crust, calcium forms more than 3% of the earthís crust. It is an essential part of leaves, bones, teeth, and shells. Calcium is never found in nature uncombined with another element. It is often found as limestone, gypsum, and fluorite. Calcium has a silvery color, is hard, and is produced by running electric current through fused chloride to which salt (NaCl) to lower the melting point. It is one of the alkaline earth elements; it readily forms a white coating of nitride in air, it reacts with water, and it burns with a yellow-red flame. Its natural and prepared compounds are widely used.*.

Quicklime, or lime, as it is more commonly called, is calcium oxide (CaO). It is a white alkaline substance having considerable power to corrode, or eat, animal tissues. Quicklime is usually obtained by roasting limestone in a kiln or furnace at about 1,800º F (980 ºC). This changes the calcium carbonate of limestone to calcium oxide. Since lime is alkaline and chemically active, it is useful in many processes. These include removing hair from hides and reducing acidity in soils and various liquids. Other common uses are in making mortar and plaster and in the manufacture of glass, paper, and steel.

To make mortar, lime is slaked, or broken down, by adding water. This changes the substance to calcium hydroxide, Ca(OH)2. Coarse sand, cinders, or pulverized stone is mixed in, and the mixture is used to bind or cover bricks or stones. As the mixture dries, it absorbs carbon dioxide from the air to form calcium carbonate and combines with the silica of the sand to form calcium silicate. These substances bind the bricks or stones together. Lime exposed to air is ruined for mortar making because it absorbs carbon dioxide from the air (air slaking). Mixing hair with waterslaked lime makes lime plaster.

Melting limestone, chalk, or oyster shells in an electric furnace forms pure calcium oxide. Under intense heat, pure lime gives a strong white light. Limelights, also called calcium or Drummond lights, were formerly used in stage lighting.

A solution of calcium hydroxide in water is called limewater. This is used in medicine to correct acidity, to prevent milk from curdling in large lumps, and in certain oils as a liniment for burns. Limewater is also an antidote for poisoning by mineral or oxalic acids..

Some important facts that need to known when making a fresco would start with slaking the lime (putting in into water). The mixture will need to be set aside for at least three months. After the panels are setup, plaster should be applied. Plaster is applied in five coats. There are this many coats in order to give strength, to prevent cracking, and to extend the life (or painting time) of the final coat. The first coat consists of 1-1/2 parts mixture of sand or marble dust, one part cement, and one part lime putty (slaked lime). The next three coats consist of two parts medium sand or marble dust and one part lime putty. The mixture will not set unless exposed to air. The first coat must be wet down before the application of the second. The second is applied in the same manner and must be wet down before the third coat is applied. This third coat in mural painting is called sinopia, where the drawing is enlarged, drawn on over the entire wall, corrected for perspective and errors, all in red ocher pigment and water. After tracing, the final two coats are applied over just the area to be painted that day. The proper pigments for use in fresco are oxides of metal, mostly earth colors, e.g., vine black, red ocher, burnt sienna, cobalt blue, raw sienna, viridian green, yellow ocher, terre verte (green earth), Mars yellow, Mars black, Venetian red. The pigments must be limeproof and sunfast. Lime is caustic and will burn through most organic or man-made pigments. The 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. Now, it is almost time to paint. The third coat must be wet down before the application of the fourth. The fourth coat is applied, worked, and floated in the same manner as the third. This coat must be left alone for 15 minutes to an hour to set. The fifth and final coats consist of one part sand or marble dust and one part lime putty. In order to test the surface for paint readiness, a brush can be dipped in water maybe stroked across it. If the water is directly absorbed, the surface is ready. The drawing is laid on top and pounced. Some other important facts about painting starts with the pigment being applied thinly with water, waiting 15-20 minutes between coats, allowing the crystallization process to lock-in each layer. There are many steps involved with specific details to make a decent fresco that were left out and that I decided to focus more on the chemistry aspects of making the fresco***.

A good web site with more information on preparing frescoes.