Here’s where the “White Shirt” painting is at. What I’ve done is finish initial rendering of each area of the shirt. I found that the hues were uneven—I am still learning to manage near-neutrals across relatively large areas of a painting. What I tried was to glaze transparent yellow oxide across bluer shadow areas, which evened out hues somewhat, but the overall painting was unconvincingly yellow-orange. I had also over-rendered much of the shirt, with too broad a range in value between darks and lights.
This was a perfect time to apply a velatura.
Taking a hint from Tad Spurgeon, I mixed up a batch of putty. This was calcite (ground marble dust) mulled with walnut oil and a bit of stand oil. The resulting mixture was a dull grey with the consistency of, well, oil paint. Putty is a medium used to increase the transparency of paint, since the calcite is essentially invisible in an oil vehicle. This is better than adding a lot of oil or resin, as the calcite/oil mixture is as strong and as resistant to discoloration as oil paint.
I mixed the putty with lead white (Doak’s flake 1C) in approximately equal amounts. Then I added a very small amount of neutral gray paint (ivory black and burnt umber) which I had previously tubed. I now had a very light gray, relatively translucent mixture.
I oiled out the surface of the painting with a thin layer of walnut oil, which is very slippery and less yellowing than linseed. I applied the gray mixture to the surface. Initially, it looked awful—my careful painting was covered with flat gray. With a stiff bristle flat, I started working at adjusting the thickness of the velatura layer, pulling the underpainting out. I found that it was effective to moisten the brush with a bit of walnut oil. It took awhile, but eventually the underpainting began to show through, with the value range compressed toward the gray value of the velatura and the hue pulled toward neutral.
It needs a bit of work once the velatura layer has dried to restate a few highlights and dark accents, but overall this was a successful exercise.