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Intonaco is an Italian term for the final, very thin layer of
plaster
Plaster is a building material used for the protective or decorative coating of walls and ceilings and for Molding (decorative), moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of ...
on which a
fresco
Fresco (plural ''frescos'' or ''frescoes'') is a technique of mural painting executed upon freshly laid ("wet") lime plaster. Water is used as the vehicle for the dry-powder pigment to merge with the plaster, and with the setting of the plaste ...
is painted. The plaster is painted while still wet, in order to allow the pigment to penetrate into the intonaco itself. An earlier layer, called arriccio, is laid slightly coarsely to provide a key for the intonaco, and must be allowed to dry, usually for some days, before the final very thin layer is applied and painted on.
[Ugo Procacci, in ''Frescoes from Florence'',pp. 15-25 1969, Arts Council, London, gives a full account of the process.] In Italian the term intonaco is also used much more generally for normal plaster or mortar wall-coatings in buildings.
Intonaco is traditionally a mixture of
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
(with granular dimensions less than two millimeters) and a binding substance.
Types of intonaco
Different types of intonaco are classified based on the binding material used:
* Intonaco based on
lime
Lime commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Botany ...
, where the only binding substance is
hydrated lime
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has ma ...
* Intonaco lime/cement, where the binding element is a mixture of hydrated lime with
Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
, with a majority of lime
* Intonaco cement/lime, where the binding element is a mixture of hydrated lime, and Portland cement, with a majority of Portland cement
* Intonaco with a plaster base, where the binding element is exclusively plaster
The
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
utilized in the intonaco can be
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
or
silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
, taken from a natural source such as a river or from sand that is pulverized.
Types of stabilizers
Intonaco can be stabilized using:
* Lime
* plaster
* Calcium-sulfate based plaster
* Terracotta-based cement
References
{{reflist
Painting techniques
Plastering