I recently attended a workshop at Bangalow with Jenny Sages. it was an opportunity to learn how Jenny does her wonderful works. It seems that those huge portraits are painted in oils on a wax ground, so they are not really encaustic paintings. The wax ground gives the paint a beautiful luminosity, and a kind of warmth to the skin tones which would be very difficult to achieve in any other way.
Here are some images from the workshop.