One can immediately see the same pose by this middle aged woman in both the painting and the drawing. Within the drawing that is in front of us, the darker lines indicate the part of the composition in which Gauguin was most focused. Her outline of shoulder and arm help him to plan out how he would construct the layout of the bar behind her. Her constructs her facial features accurately, but without going into too much detail beyond the key elements, such as her nose, eyes and hair. Her expression is fairly neutral but clearly she had something that artists liked in terms of her appearance because Vincent van Gogh would also produce several depictions of her as well. Of course, the two artists were living together in Arles at the time and would use the same content several times.
Having been drawn and painted by two of the most famous European artists of all time, there has been great interest by academics into this series of work. We do know that both drawing and painting came about in 1888, with the former having been produced in charcoal. Gauguin himself worked with various mediums for his sketches, including standard pencils and also chalk. He also used pen sometimes, but not as frequently. If we look directly at the artwork in front of us here, we see that many of the solid forms are only very loosely filled in with diagonal lines as if to finish the piece but without as much care as delivered on the outlines. It looks like the sort of artwork that could have been completed fairly quickly, just in an hour or so and may even have been performed at the same time as he begun on the more well known painting.
You will also find some notes written on the artwork, to the side. This underlines how Gauguin considered this to be a study piece, and so was happy to leave points of thought alongside the portrait so that he could lead his mind when he referred to it at a later date. It is important to remember that the two great names of Gauguin and Van Gogh were not seen in that way during their own lifetimes, and so they would not have imagined that their study drawings would have become as well known and valuable as they are today. In fact, they would likely have been shocked by the attention given even to their incomplete artworks, as well as the values now being received at auctions for their work, though that would be the opinion of most artists from the mid 19th to early 20th century who simply wanted to innovate and influence with new ideas.