a very bad state of preservation, or, if they have fallen into the hands of restorers, they will in many instances have been greatly changed. Some of the restorations go a long way back. In certain ancient account books mention is made of sums to restorers as long ago as the fourteenth century. These restorers did not always take the trouble to remove the protective layer of varnish; they were satisfied to patch the painting on top of the colors which had faded or had otherwise chemically changed. Later, in the seventeenth century, paintings were all simply restored in oil, regardless of the original technique, and this very often altered them beyond recognition.

    Fortunately, we still have the old illuminations in books where the same technique was employed as in paintings that were to be hung on walls. These were executed by the same masters but as in the books they were preserved without varnish, the colors have kept the original tones. Some of them look as if they had been painted only yesterday. By comparing these illuminations with the wall paintings of the same time (which were varnished) we can see the extent to which the use of the oil varnish, which covered the latter, altered their color. For instance, the blue mantles of the Virgins, particularly those of the school of Sienna, turned almost black as a result of the oil varnish, whereas these mantles painted with the same blue in the illuminations have kept their original light blue color.

     The difficulties we therefore encounter in attempts to reconstruct the actual processes by which these tempera paintings were executed can be readily appreciated. One thing that remains clear throughout our studies is the fact that these early artists were struggling with an extremely refractory material and were compelled to resort to certain conventions which, whatever our estimation of their final result, was a matter of necessity rather than of choice.

One of the tempera artists' chief difficulties came from the impossibility of direct painting with his medium. Because of the rapid evaporation of the water with which the colors were mix the painting dried too fast for the artist to blend his colors. Another difficulty was that many of the colors under-

* 24 *