... we see colors not in their original state but as time has made them. This work of time—whether due to the chemical evolution of the colorant materials or to the actions of humans, who over the course of the centuries paint and repaint, modify, clean, varnish, or remove this or that layer of color set down by preceding generations—is in itself a historical document. That is why I am always suspicious of laboratories, now with very elaborate technical means and sometimes very flashy advertising, that offer to "restore" colors, or worse to return them to their original state. Inherent here is a scientific positivism that seems to me at once vain, dangerous, and at odds with the task of the historian. The work of time is an integral part of our research. Why renounce it, erase it, destroy it? The historical reality is not only what it was in its original state, but also what time has made of it. Let us not forget that and let us not restore rashly.
Black—The History Of A Color, Michel Pastoureau 2008, (my emphasis below).
The work of time is an integral part of our research. Why renounce it, erase it, destroy it? The historical reality is not only what it was in its original state, but also what time has made of it.
I think the 'restoration' of paintings is not that at all; it is simply the repainting, or more exactly, the over-painting by another person at a later date. I prefer seeing "the work of time" or the decrepitude of aging that adds a realness to the painting.
Moreover, quantities and proportions are always quite inexact: "take a good portion of madder and put it in a certain amount of water; add a bit of vinegar and a lot of tartar." The same imprecision applies to the length of time one should boil, decoct, or soak the cloth, which is rarely indicated or else highly implausible. A text from the late thirteenth century, for example, explains that to produce green paint, copper shavings should be soaked in vinegar for either three days or nine months. As is often the case in the Middle Ages, the ritual is more important than the result, and numbers are more symbols than actual quantities. For medieval culture, three days or nine months represented more or less the same thing in that both expressed a period of waiting and (re)generation—Christ's resurrection occurred on the third day, a child arrives after nine months. It is typical of medieval thinking to superimpose such symbolically significant periods on other spheres of life and activity.
Blue—The History Of A Color, Michel Pastoureau 2000.
But I like the thirteenth century way of proportions and time; they're very similar to the directions for cooking in Larousse Gastronomique, 1938. One doesn't follow the recipe blindly, one creates as one goes—it doesn't always work—and that's what makes it so special when it does.