Parkhurst's mention of that particular variation of the indirect technique only corroborated my own observations of many Bouguereau paintings analyzed from very close range with my own eyes. It is there to be seen in many of his paintings from the last 35 or so years of his life, if one looks closely enough. It's true that he began the paintings with the inking of the charcoal line drawing, then did a frottis, then an ebauche, then the fini, as was pretty much standard academic practice, but his handling of flesh was as I described, in the last two stages, at least late in his career, from his late forties onward, when his work made a noticeable improvement over the early and middle periods, during which I do not doubt that he worked more opaquely.
I'm relying on my own visual analysis of the paintings in discerning WB's employment of this method, and also of Boucher's, though Boucher did not do it as well. One clue is in The Broken Pitcher, in San Francisco, where Bouguereau scratched through the top layer, a thin, semiopaque scumble of greyed fleshtone more grey than color, with the handle of the brush to indicate a crease in the skin inside the elbow of the girl's arm, revealing a higher-chroma opaque underlayer, obviously (on close inspection) greyed-down by the superimposed more neutral scumble. But it can be seen in many other of his paintings as well. Only the lightest lights are fully opaque, though the areas near the highlights approach full opacity.
I was thrown out of the chapel at the Forest Lawn Memorial Park, in Glendale, California, for climbing up on the altar that is part of the frame for the Bouguereau painting that is there, which I had to do to get a good look at WB's handling of the flesh of the figures in that painting. I got what I came for before I was discovered, and it confirmed my suspicions, as did many other Bouguereau paintings I've sought out around the world. This is not an idea I got from Parkhurst or anyone else, but when I reread Parkhurst, it was there as well. I had already figured it out on my own before I ever noticed Parkhurst's mention of it. Mark Walker made no mention of it in his accounts, and so it seems he missed it, but it is there to be seen if one knows what to look for and where to look for it. If you're ever coming to San Francisco, I can show you.
I suggest you try the technique, too, just to see for yourself how well it works. The principle is the same as that seen in real skin of light-complected people. The top layer of skin is pretty much neutral in chroma, with the color coming through from below, seen through the semi-opaque white or light grey of the upper layer of skin. If you have ever peeled badly from sunburn, you might have noticed that the skin that peeled off had no color of its own. The technique I've described duplicates that same optical sensation in paint. It starts showing up in Bouguereau's work beginning around the early 1870s, and perhaps one or two from the late 1860s. I can show you many examples. It does not come through in reproductions, unfortunately, as the paintings are quite large, and the reproductions shrink them down too far for precise reading of these things. Look at the originals again, with what I have said in mind.
Virgil Elliott