Question: Who was the model for Van Gogh's art?
About the article "Sien (Van Gogh series)", section "Abstract".

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Art dealer Pierre Firmin-Martin, a friend of Van Gogh's brother Theo, displayed some of Van Gogh's paintings.
"Mother by a Cradle, Portrait of Leonie Rose Davy-Charbuy" was made of Martin's niece who lived with her uncle.
Reflective of the family's interest in art, paintings hang in the background.
In the year the painting was made Theo commented that Van Gogh done a good job painting portraits but had never asked for payment. 
Adrianus Jacobus Zuyderland was Vincent van Gogh's favorite model during his Hague period.
He appears in dozens of drawings, easily identified by his bald head and prominent white whiskers, and he was the model for the drawing which was the basis for van Gogh's later iconic painting "At Eternity's Gate". 
Vincent van Gogh's grandfather (born 1789) was also named Vincent van Gogh.
According to Vincent van Gogh's first biographer, his sister-in-law Johanna van Gogh, the grandfather was a pastor, and the son of Johanna van der Vin of Malines and Johannes van Gogh.
Johanna van Gogh writes that Johannes "was at first a gold-wire drawer like his father, but he later became a Bible teacher and a clerk in the Cloister Church at The Hague."
She describes him as an intellectual, duty-bound man who was awarded prizes and testimonials for his distinguished work.
A family legacy, from Vincent's great-uncle—a sculptor and a lifelong bachelor—allowed Vincent van Gogh (Johannes' son) to study divinity at the University of Leiden.
After successfully completing his studies and having become established at the parsonage of Benschop, Vincent van Gogh married E. H. Vrydag in 1810.
They remained married until Elisabeth's death on 7 March 1857; the Reverend Vincent van Gogh lived until 1874.
In July, 1881 Van Gogh made "Portrait of Artist's Grandfather" (F876).
The work was drawn in pencil and brown ink.
Then he used opaque white watercolor and a brown wash.
The drawing is owned by the Van Gogh Museum in Amsterdam. 
"Vase with Zinnias and Geraniums" (F241) reflects the influence of Adolphe Monticelli (1824–1886) in its vivid color and impasto paint.
Van Gogh admired, and later collected, Monticelli's work.
Van Gogh had been introduced by his brother Theo to Monticelli's still life work with flowers in Paris.
He admired Monticelli's use of color as an expansion of Delacroix's theories of color and contrast.
Secondly he admired the effect Monticelli created by heavy application of paint called "impasto".
It was partially Monticelli, from Marseilles, who inspired Van Gogh's southerly move to Provence in 1888.
He felt such kinship for the man, and desire to emulate his style, that he wrote in a letter to his sister Wil that he felt as if he were "Monticelli's son or his brother."
The first owner in the provenance of this painting is "C.M.
van Gogh Gallery, Amsterdam, The Netherlands", which was owned by Van Gogh's uncle and an art dealer, Cornelius Marinus van Gogh (1824–1908).
"Bowl with Zinnias and Other Flowers" (F251), painted within days of "Vase with Zinnias and Geraniums" (F241), is evidence of Van Gogh's transition to a lighter color palette.
Picking up elements of Impressionism Van Gogh painted with a more vigorous brushstroke, with thick application of paint, called "impasto" which created a three-dimensional relief.< 
While in Saint-Remy interest began to build in van Gogh's work:   Theo, Van Gogh's brother, wrote in July 1889, that Camille and Lucien Pissarro, Père Tanguy, Erik Theodor Werenskiold and Octave Maus, secretary of the Les XX group in Brussels, had seen the paintings that he'd made in southern France.
On Van Gogh's behalf, Theo accepted an offer from Maus to exhibit Van Gogh's work at the Les XX group's upcoming exhibition.
Van Gogh's "Starry Night over the Rhone" and "The Irises" were exhibited at the Société des Artistes Indépendants on the third of September.
In January, 1890 six of Van Gogh's works were exhibited at the seventh exhibition of Les XX in Brussels along with, among others, Paul Cézanne, Camille Pissarro, Pierre-Auguste Renoir, Paul Signac and Henri de Toulouse-Lautrec.
Van Gogh's painting "The Red Vineyard" was sold to artist Anna Boch at the exhibition for 400 francs.
In the same month an article is published "Les Isole: Vincent van Gogh" in the "Mercure de France".
Ten of Van Gogh's works were presented at the March, 1890 Société des Artistes Indépendants.
Paul Gauguin, Claude Monet and Pissarro were quite impressed with his works.
Over this time, though, Van Gogh's health ebbed and flowed between periods of attacks, recovery and resumption of painting.
In April, 1890, near the end of van Gogh's stay at Saint-Paul's hospital, Theo wrote to his sister and mother, "I am so pleased that Vincent's work is being more appreciated.
If he were fit I believe that there would be nothing for me to desire, but it appears that this is not to be.
"The sale of "Red Vineyard" was the only sale of van Gogh's paintings made during his lifetime.