The Exploiters – 1926 – Fresco
Universidad Autonoma de Chapingo Chapel, west Wall
Although it has been documented that some form of Buon Fresco (true fresco) was painted on the limestone walls of the caves, and has survived eras as far back as 30,000BC, the procedure was perfected in16th-century Italy. Not to be confused with fresco secco “dry”, which was painted on dry plaster with pigments in a glue or casein medium, boun fresco is said to be a difficult media for a painter to work with because it involves a swift method of painting on fresh wet plaster in giornata (one day sections). A physically demanding art form, fresco is one of the most permanent means of decorating architectural spaces with mural paintings. With fresco the artist mixes pigments with water and/or egg yolk and paints into different grades of a sand and lime plaster mixture which absorbs the color. The plaster then hardens back into a colored limestone leaving much of the original mineral sparkle unchanged.
In the medium’s chemical process a preparation known as “Slaking” involves adding water to quicklime, or calcium oxide, to produce calcium hydroxide. The chemical reaction will produce heat depending on the consistency of the mixture. Calcium hydroxide is aged and can be stored indefinitely under layers of milky “limewater”. When applied it combines with carbon dioxide in the air to form calcium carbonate and water. Particles of pigment then harden while the water evaporates producing the shimmering matte finish that is distinctive in frescoes.
Originally boun fresco techniques had been designated only to architectural applications such as on walls and ceilings. In limited size due to weight, today the techniques have carried though to paintings that can be transported and used the same as paintings. Traditional fresco starts with a brick or stone wall where the first scratch coat rough layer of plaster is laid. Any old plaster or stucco needs to be removed down to the bare brick or masonry. All old metal construction materials should be cut and sealed to prevent rust from migrating to the surface. Since modern construction uses sheet rock if the area to be painted has been at least primed (old paint is fine) or sealed from moisture, the work would start with attaching galvanized metal lath anchored to the supporting studs similar to the method used for exterior masonry over wood frame construction. You are now ready to start with your first layer.
Minimum tools required for this job would be:
- Goggles and Rubber gloves to protect yourself from lime burns (check MSDS for lime hazard precautions)
- A tub to mix your plaster in
- Various trowels such as a 8X3 steel notched scratcher trowel, a rectangular finishing trowel and a wooden float
- Natural hog bristle brushes made to withstand the alkalinity of lime.
The surface of the (trusillatio) is combed or “scratched” in multiple directions to provide tooth for the subsequent layers to grip to. This can be accomplished in one or multiple layers. When applied to a masonry wall this layer is generally near 1/3″ thick. The plaster at this stage usually contains a larger ratio of sand than lime as well as a small quantity of cement. Never use ocean sand since it’s salt content will cause deterioration. Modern applications include fiberglass hairs with an acrylic fortifier to strengthen the surface. Always use distilled water throughout the process to prevent contaminates from interfering with the bond. This stage should allow 3 to 5 days to dry.
As the layers progress the percentage of lime in the plaster increases. After wetting the first layer, you would skreet or level off the first coat with a stucco textured coating which is known as the (arriccio) or “brown,” layer of plaster in fresco painting. This is a layer of 2 to 3 parts sand to 1 part lime. At this point your masonry wall is prepared for the painting.
The Italian method of fresco painting produces the richest colors and the most durable bond with watered pigment using plaster as the binder. However, not unlike many other complex mediums, this is not a medium that performs well to experimentation. Much of the fresco painting method demands meticulous preparation. The rewards are only realized after careful and diligent planning prior to actually starting the painting. In the beginning when the artist starts to plan his project he draws a succession of small color studies (bozzetti) to focus on color, perspective, and composition. With the bozzetti, the artist creates “cartoons,” or a full-size drawings made on paper done in charcoal scaled as they appear in the painting. Perforated tracings are then made of the cartoons with a needle and these perforations are then pounced by dusting it with a Powdered Charcoal -filled bag to transfer a dotted outline of the image on the surface to be painted. Over the 2nd layer of plaster known as arriccio , the artist paints over the dots left much like a imprimatura with a water brushed red, green or brownish earth earth color pigment called sinopia. Consider this as an important step to allow for analysis of the composition and scaling revisions. Once the artist is certain about he final appearance it is time to apply the third and final (intonaco) with a mixture of 1 part fine sand to 1 part lime applied 1/8″ thick which is the most sensitive layer of plaster in a fresco painting. We quickly move on to the second and final cartoon pouncing and sinopia to outline the final painting. Modern methods extend to the use of stencils and projectors to obtain satisfactory results where as the artist can move strait to the intonaco, final cartoon and sinopia if properly planned.
Fresco, demanding mostly natural mineral Pigments, does not permit a large palette due to it’s high alkalinity where not all colors are non-reactive to lime. The plaster must be painted while it is wet with paint brushes specially made from boar’s hair that resist the lime’s high alkalinity. Since all fresco painting should be completed in one day, it is a good idea to have the majority of your basic colors premixed. Trowel or float the intonaco only in an areas you can finish by the end of that day. With the exception of fresco secco, the fresco painting can not be painted over. Fresco painting on dry plaster or (fresco secco) should be done sparingly. It not only alters the over all appearance of the art, it will eventually crack and flake off as well. Any area of the painting where the artist has made an error must be scraped off including the intonaco, re-plastered and painted from the whole days session.
If you want your painting on a panel it is not necessary to have as many layers of arriccio for panel work and your finished layer can be applied directly to your scratch coat. Although this is a modern method that may be classified as mixed media, with your non-traditional plaster coats you can create your work on a significantly lighter wood panel with reduced weight and the appearance very similar to traditional fresco. It is recommended to use only an exterior grade laminated plywood for this application and that the panel is made extremely rigid. Once you have made your panel to size, cut a piece of hessian burlap to overlap all four sides as if you were stretching canvas over it. Prime your board with Gamblin PVA Sizing and allow it to dry. Apply PVA size again liberally to the panel to glue the burlap to the board. and lay the hessian or jute burlap out on the board stretching it around all four sides. Go over it again with another coat of PVA size over the burlap and let it dry until tacky. Some artists put a frame around the panel to function similar to a concrete form to assist leveling the final layer. It should be no greater than 1/4″ above the surface.
For the scratch coat use Quik-Fix All Purpose Patching Compound as directed. This premix contains starch size and lime to make a strong bond, it sets fast and dries hard. This is a great short cut that you can purchase at almost any hardware or home improvement store. Spray the board with water to dampen the surface and apply a thin coat with a trowel like tile adhesive combing grooves for the top coat to grab to making a light scratch coat.
- 1 part Fresco Lime Putty (calce Florentine) 10 Kg
- 1 part washed sand, Pumice or Marble Dust
- 1/8 part acrylic fortifier
Add distilled water in moderation to obtain a gelatin or putty viscosity. After the scratch coat has dried completely then dampen it again with water from a spray bottle and apply the (intonaco) finish layer to achieve a total thickness no greater than 3/16 to 1/4″. Use your wet wooden float to obtain desired surface.
When the plaster’s surface can not be moved stoking with a brush the intonaco is set for paint. Because these coats of plaster are much thinner than traditional concrete walls expect accelerated drying. This is why you should have your colors premixed also in distilled water and a completed plan for your sinopia sketch previous to the intonaco layer. You can retard some of the surface drying by spraying any unpainted surface sparingly with water. However, you must move quickly when painting. Painting light to dark, keep in mind the colors in a dry fresco will always be lighter than when first painted and will continue slightly to diminish over time. No finish is necessary.
“The true work of art is but a shadow of the divine perfection.”