The controversy around the restoration of the Sistine Chapel ceiling in the 1990s has always struck me as odd. A surprisingly large cadre of critics objected to the brilliance of the colors when the restoration was unveiled, believing them to be too “modern”. I find this odd because it’s widely known that Mediaeval and Renaissance fortunes were made, intrigue and political manipulations abounded and, I suspect, murder was even done in pursuit of control of the components of brilliant colors.
For example, after the Ottomans gained control of and limited access to traditional sources of alum, the Papacy took aggressive steps to control new-found alum sources in Italy. One of the important uses for alum was as a color fixative in dyes and paints, the light-colored alumen being useful in brilliant colors, the dark-colored black or very dark colors.
Certain paint colors were extremely expensive. This added value – both monetary and symbolic – to any work in which they were used. For example, in the more than 50 frescoes he painted at the San Marco priory in Florence, with Cosimo dei Medici financing the work, Fra Angelico -- true to his monastic principles -- used just a single passage of pure ultramarine blue. He used it only in the most prominent fresco, to highlight the importance of the subject: coloring the Virgin Mary’s cloak the unique clear blue that only ultramarine could produce.
Ultramarine is the oldest and most technically specific device whereby a painter and his patron could honor a distinguished personage. That is because ultramarine was by far the most precious of all the painter’s materials. It's beautiful, it’s extremely resistant to the damaging effects of light, and it’s very rare. Consequently, painters’ contracts of the period frequently specified the exact quantity of ultramarine that the patron authorized the master to use. At San Marco, whose frescoes are distinctive for technical as well as aesthetic reasons, the message is clear: in the spirit of humility, the opulent blue pigment appears at San Marco only on the Virgin Mary and only in the Chapter Room.
Referring to the importance of identifying historically-true colors in art restoration, Stephanie Reitz, in an article in the ArtInfo newsletter says, “The implications go beyond aesthetics to cold cash. For example, the use of pure Prussian blue—the first synthetic color of the Industrial Revolution—can cause a painting's value to skyrocket.” So what’s changed?
Theoretical and practical approaches to art restoration change over time, influenced largely by available technologies, and also by cultural trends.
Until a quite recently, restoration and preservation was a “best guess” proposition, with the restorer -- typically an artist by training -- making assumptions about what paints, varnishes and other materials were originally used. Results varied from good to disastrous. Restorers today often find themselves having to undo ill-advised past restoration efforts.
In much the same way as a good historian pursues the truth about what happened at a distant past point in time, a good art restorer seeks to know the facts related to the creation of a particular artwork.
Today chemists are involved in restoration, using invisible-to-the-naked-eye samples of paint taken from the piece. Henry DePhillips. a Trinity College chemistry professor says, ''The whole goal of art conservation is to preserve the original vision of the artist, not my vision of what it could or should be,'' alluding to the guesswork in outdated theories of restoration.
Using cutting-edge science chemists can identify the mix of ingredients – like iron oxide, mercury, titanium dioxide, lapis lazuli -- that constitute various colors. For example, titanium dioxide is what made white, white.
“If you're going to restore a piece of art to the way it was on the day it was finished, you need to know exactly what materials they used. Our job has been done correctly if you, a viewer of the piece, cannot tell that anything has been done,'' DePhillips said. ''That is meeting our responsibility to history.''