When I first started exploring portrait painting with oil, the main challenge was always achieving a likeness of the face. I admit that it is still something I care about today.
Portrait painting is an interesting art form and I believe many people will agree with me that it is more challenging compared to still life and landscape painting
Without careful observation of the face's features, proportion, and ratio, it is easy to make a person look like someone else. When the likeness is off, it can be a source of embarrassment for some portrait artists, especially when the general public holds only one perspective when viewing all portrait paintings.
I understand that likeness is the number one thing that people use to judge between good and bad artists, and that's why many artists strive to fulfill this criterion, regardless of their opinion about what makes a truly amazing portrait painting. Likeness is not unimportant, but if we look at art history, it is not meant to be the only criterion. If it were, many famous artists in history would not enjoy the fame they have today.
The first portrait that I think I achieved 80% likeness was the painting of Daniel Craig. By having a pencil sketch before applying the oil paint, I made sure the likeness was achieved so I could just let my brushes follow the lines without too much effort.
However, my mindset changed a little after completing a few portrait paintings. I started to get rid of pencil sketches. It wasn't because I was so confident in my observation or painting skills, but quite the opposite. With a pencil sketch, I stopped paying attention to constantly judging and amending the painting, which is not a good idea, especially for portrait painting. It put me in the wrong place where I would blindly follow the lines and make more awful mistakes.
Secondly, I found that a good portrait painting contains many different qualities; likeness is just one of them. If we just pursue 100% likeness at all times, we would fool ourselves into achieving a photo-realistic level that doesn't allow for other art possibilities. Don't get me wrong, I appreciate the tremendous effort and hard work that goes into achieving a high level of likeness.
With these understandings, sketching a portrait with oil paint is no longer a fear for me. At the same time, I started my separate pencil sketch to improve my drawing skills, and as far as I enjoy the pencil sketch, I know it will benefit my oil portrait painting in terms of sharpening my observation and making my brushstrokes more precise over time.