The artist painted thick, gestural brushstrokes with layered globs of paint onto his canvases to create a sense of energy and movement. He wanted to create and inspire feeling, emotion, even passion into his artwork. This gave his approach to form a completely new look, but it also inspired his bizarre methods of painting. In this Still Life of a Vase with Twelve Sunflowers we can clearly see the artist's brushwork. Click on the image and enlarge it to see what I mean.
Van Gogh sometimes squeezed paint straight out of the tube onto his canvas and used his fingers to brush it one way or another. Some of the thick globs of paint on his works are still wet today, there is simply so much paint there. Talk about an overflow of emotion—the artist has almost poured out himself, in paint, onto the canvas. Flowers are a delicate subject matter, but here we see an excess of paint and flood of bright, neon colors. Granted, sunflowers are larger and bulkier plants than tulips, but Van Gogh's thick paint goes a level too far. And observe his signature, one of the largest in the history of art: "Vincent" across the front of the vase in bold, noticeable letters—not his last name, which would be more professional, but his first name, more familiar, more honest, more open. He is putting himself down into his painting.
This allows for an unprecedented level of stylistic uniqueness that distinguishes this artist from all the rest. When we look at a Van Gogh painting, we are very aware that we are looking at a painting by Van Gogh. This is the way in which he paints. His art is, in a sense, a conversation with himself; and we as viewers are allowed in on the intimate discussion of color, shape, and design. In truth, the artist's works were very personal to him. Since Van Gogh wrote so many letters and documented his life in writing so thoroughly, we (on a surface level, at least) basically know everything about his life; and this allows us to enter into the world of his artwork. This otherwise personal area of his private life is revealed to us as the ultimate form of Post-Impressionist method: the Impressionism of oneself. This was a matter of self-expression for the artist, not about outside subject matter or the patronage of any viewership within the public sphere. In his entire life, Van Gogh only ever sold one painting, and that was to his brother, Theo.