Above is a Youtube video of some film dated September 1928 of Philip de László painting a portrait. Hungarian born Philip de László had a brilliant career painting the portraits of numerous European royals and noblemen from about 1890 to his death in 1937.
The film shows him placing the canvas alongside the model and standing back to view his painting and the model together. This is the sight-size method of painting although in my opinion, Laszlo is standing a bit too close to the canvas for it to be fully sight-size. What I find interesting is that he first paints part of the outline of the figure and then some of the background, rather than the face. He also uses his mahlstick a lot, paints directly onto the canvas, although he does make a small preliminary graphite sketch, and has the model sitting in strong flat light (i.e. facing the light). Flat light can produce glare on the canvas but László seems to manage beautifully. Below, a few of his portraits.