What Basic Materials Do Artists Use to Make a Fresco?

What basic materials do artists use to make a fresco?

The interior of the Sistine Chape

The interior of the Sistine Chape, Michelangelo

Artists making a fresco use lime plaster, water, and dry-powder pigments. The process involves applying these materials to a wall while the plaster is still wet. This chemical reaction integrates the pigment into the wall surface, creating a durable, permanent artwork that becomes a part of the architecture itself.

The foundation of a fresco is built through several layers of plaster. The process begins with a scratch layer used to prepare the wall and serve as a binder. This is followed by the arriccio, a rough underlayer containing more lime than the aggregate. Finally, the artist applies the intonaco, which is the smooth, final layer of plaster on which the painting occurs.

The specific ingredients used in these layers include:

• Lime: Often prepared as grassello di calce, which is slaked quicklime in excess water.
• Aggregate: Typically sand, though Michelangelo used volcanic ash in the Sistine Chapel to allow for smoother spreading and quicker drying.
• Additives: Coccio Pesto, a mixture of crushed terracotta or brick and lime, can be used to create stronger plaster.

What type of plaster is required for the buon fresco technique?

The buon fresco technique requires layers of lime plaster applied to a wall. The artist works on the intonaco, the final smooth layer, while it is still damp. Because the plaster must be wet for the pigment to bond, artists work in sections called giornate, or "a day's work."

The preparation of the plaster is a precise process. The arriccio layer is applied to the wall and allowed to dry for several days. Once this is set, the artist may sketch the composition onto the arriccio using a red pigment called sinopia. This serves as a blueprint before the final intonaco is laid down.

The chemical transformation is essential to the technique. As the wet lime plaster dries, it undergoes carbonation, turning into calcium carbonate. This process locks the pigment particles into the crystalline structure of the wall, ensuring the colors remain part of the solid surface rather than a superficial layer.

What are the primary pigments used in fresco painting?

Primary pigments for buon fresco must be natural mineral pigments that are stable in an alkaline environment. Because the lime is highly alkaline, artists must use colors that will not fade or change. These typically include earth colors, clays, and various mineral oxides that are insoluble in water.

Commonly used stable pigments include:

• Earth tones: Ochre, terre-verte, and hematite.
• Whites and Blacks: Lime white (also known as bianco San Giovanni) and black pigments like vine black (PBk7) or ivory black (PBk9).
• Other minerals: Giallorino and cinabrese.

Not all pigments are suitable for the wet lime process. Certain colors are considered unstable or incompatible with the alkalinity of the plaster. These include azurite, verdigris, orpiment, red lead, white lead, vermilion, and lac. These pigments are often applied later using the fresco secco method, where they are bound with an organic medium like egg or glue.

What tools and binders are necessary for the process?

In buon fresco, water serves as the primary vehicle for dry-powder pigments, as the lime itself acts as the binder. However, for fresco secco—painting on dry plaster—artists require additional binding media such as oil, glue, casein, or egg tempera to ensure the pigment adheres to the surface.

To transfer a design from a full-scale drawing, known as a cartoon, to the wet wall, artists use specific tools and methods:

• The Cartoon Method: A cloth veil with holes pricked through the design is held against the wall.
• Spolvero: A technique where colored powder is dusted through the holes in a cartoon to create a dotted outline.
• Fresco Lustro: A technique used in works like the Sigiriya paintings that involves a mild binding agent or glue.

The choice of water is also a factor in the preparation. While distilled water is used in some settings, traditional fresco work often utilizes clean water, such as rain or spring water, to ensure the purity of the mixture.