Fresco Technique
True fresco (an Italian word meaning fresh) is the process whereby paint is applied to wet lime plaster and is bound to the wall by the lime as it sets. Secco is when paint bound with some glue (usually casein or egg) is applied to already dry walls. Fresco is undoubtedly the more permanent of these two methods and, if done well, produces the more beautiful colours.

A summary of this ancient technique that I use is as follows. The preliminary designs are made in conjunction with the client, and when finalized, are made into full-scale drawings.

The walls and ceilings to be painted are inspected to ensure that there is no ingression of dampness and are sound. The wall is first cleaned and well wetted, and the first layer of plaster applied, about 2 cm thick. This is usually a mix of one part lime putty to three parts of graded coarse to finer sands. Sometimes some of the sand is replaced by straw or fibre such as hair or flax. The surface is left rough. The second layer is then applied, a mixture of one part lime to two parts of a finer graded sand, and is about 1 cm thick. This is finished with a wooden float and left averagely rough. The third and final layer (“intonaco” in Italian) onto which one paints consists of one part of lime to one part (sometimes less) of fine white sand or marble powder. This is only about 2 mm thick and is highly polished with a metal float prior to the day’s painting. After the surface has begun to become absorbent (a few hours) the designs on paper are applied to the wall and the basic lines inscribed. Then the painting begins.

There are variations in the timing and details of this plastering and painting process, allowing from one to up to three days painting on an area of intonaco. But the essential thing is that paint must not be applied to plaster which has begun to set (the reaction called carbonisation). This is usually eight to ten hours after painting has begun. After the area of intonaco has been painted, the unused areas are then removed, and the next day the next area of intonaco is applied.

The paints are simply a mixture of finely ground pigment and water (or sometimes water with a little lime, called lime water). There is a limited range of pigments suitable, since lime is caustic and reacts with some. The earth colours are all useable, and are by far the most commonly utilized.

As the water moves towards the surface of the plaster through evaporation it carries with it lime in solution. This lime [Ca(OH)2] gathers around the particles of pigment and as the water evaporates the carbon dioxide in the air is absorbed, causing the lime to become calcium carbonate [CaCO3], which is its original form. It is this carbonisation that locks the pigments into the wall.

Aidan’s commissions include: the chapel of the Monastery of St. Antony and St. Cuthbert, Shropshire, England (view on this website and on www.orthodoxmonastery.co.uk); the chapel of the Protecting Veil in Limni in Evia, Greece; HRH The Prince of Wales.