The detail (above) from Van Loo's painting, Marie Leszczinska Queen of France, is fascinating to me. I've been trying to figure out why I think his rendering of the gold table is unsuccessful. Though he's obviously a meticulous craftsman and clearly spent ages with a magnifying glass in one hand and a paintbrush in the other, there's something overwrought about the brushwork. His table looks plastic, but it took me a while to figure out why.
|Charles de Solier, Hans Holbein the Younger|
Holbein was, of course, a master at painting the detailed effects of light and shade on any number of textures. I examined his Portrait of Charles de Solier (above) for clues as to his technique for painting gold.
Local color and value are notoriously hard to read, so I took color samples from the sword handle, (a) through (e) above, and then de-saturated them to get their values. Applying these five values against Munsell's value chart shows some interesting results.
The values are all gathered tightly around the bottom of the spectrum, between Value 1 and 3. There is nothing at all in the mid-tones from 3 all the way to 6, when all of a sudden we have our one and only highlight, (e). What surprised me was just how dark everything was. Even the brightest highlight on gold is only a 6, yet the highlight still jumped a full three values from it's closest neighbor.
I knew that medieval painters, when planning to include gilding in a painting (say, on a halo), would map out their value composition as if the gold leaf was a dark element. This initially seems counter-intuitive -Gold isn't dark! - but when we see how dark the overall value scheme of gold is in the Holbein painting we can see why it works.
I tried the same experiment on another sample, this time a much brighter 'gold', taken from Le Brun's Hall of Mirrors painting in Versailles...
Firstly, it's interesting to note the palette swatches taken from the 'gold': They're kind of a dull brown, and not very gold at all. Again, regarding the values, we see that the majority of values are between 2 and 5, and the highlight jumps three values but is still no more than an 8.
Le Brun has used a mid-tone (d) on the circular frame, but the egg-and-dart molding has no (d) tone; it makes the 3-value-jump from dark tones straight to highlight just as in the Holbein painting, and is very successful for it.
Why is it that Van Loo's painting is unsuccessful?
Yikes! The first thing that stands out is the number of colors. Van Loo went a little overboard unnecessarily. The more colors you lay down on a space, the more you're making me stare at that area in order to figure out what's going on. Don't make me focus too much on a background object: the focus should be on the main subject.
Let's look at it more closely. Seen as black-and-white value reductions, the spread across the spectrum is much more evenly spaced than the (better painted) Holbein. Specular highlights on metallic objects are supposed to jump out at us. Van Loo's spectrum looks more like that of diffuse light, not specular.
If you want to represent specular highlights on metallic objects, you need to jump at least three values beyond your mid-tones. The way to do that is not to brighten the highlights, it's to darken everything else. Van Loo had nowhere to go from Value 7.5, as Value 10 is pure white, and as such is a purely theoretical limit.
It's like in Spinal Tap. When you turn the volume all the way, where do you go from there?
|Spinal Tap, "This one goes to 11" scene [video link]|
|Justice Punishing (detail), Noel Coypel|
David Briggs wrote a very concise description of diffuse and specular light, and explains exactly where we should place specular light reflections. Make sure to read all three pages.
Look at these examples from other painters to get an idea of their method. Notice the jump from darks straight to highlight in the Rembrandt details. I love the way he painted light on metal. You might conclude that the bigger the gap in value between shadow and specular highlight, the more successful the illusion.
|Rape of Prosperine (detail), Rembrandt van Rijn|
|Jeremiah Lamenting the Destruction of Jerusalem (Detail), Rembrandt van Rijn|
|Portrait of Pope Leo X (detail) , Raffaello Sanzio|
Ingres' detail shows the exact same phenomenon in the values on the painted gold frame. Even though the frame is in the background and the spread of values is not as great [he has rightly reserved his highest and lowest values for the main subject in the foreground], his specular reflections make the same jump.
|Still Life with Silver Jug (detail), Willem Kalf|