Question: Van Gogh wrote  "I should like to paint portraits which appear after a century to people living then as apparitons." Who did he write it for?
About the article "Vincent van Gogh", section "Portraits".

Candidate passages:
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"While Van Gogh had few opportunities to make portraits, he completed at least three at Saint-Rémy. 
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
He said of portrait studies, "the only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else."
To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"As much as Van Gogh liked to paint portraits of people, there were few opportunities for him to pay or arrange for models for his work which may have been another factor in his desire to make a portrait of his mother. 
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
He said of portrait studies, "the only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else.
"To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions -- that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character."
Although Van Gogh is best known for his landscapes, he seemed to find painting portraits his greatest ambition.
He said of portrait studies, "The only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else.
"To his sister he wrote, "I should like to paint portraits which appear after a century to people living then as apparitions.
By which I mean that I do not endeavor to achieve this through photographic resemblance, but my means of our impassioned emotions – that is to say using our knowledge and our modern taste for color as a means of arriving at the expression and the intensification of the character.
"Of painting portraits, Van Gogh wrote: "in a picture I want to say something comforting as music is comforting.
I want to paint men and women with that something of the eternal which the halo used to symbolize, and which we seek to communicate by the actual radiance and vibration of our coloring."
Van Gogh, known for his landscapes, seemed to find painting portraits his greatest ambition.
He said of portrait studies, "the only thing in painting that excites me to the depths of my soul, and which makes me feel the infinite more than anything else."
Van Gogh wrote further of the meaning he wished to evoke: "in a picture I want to say something comforting as music is comforting.
I want to paint men and women with that something of the eternal which the halo used to symbolize, and which we seek to communicate by the actual radiance and vibration of our coloring.
"As much as Van Gogh liked to paint portraits of people, there were few opportunities for him to pay or arrange for models for his work.
He found a bounty in the work of the Roulin family, for which he made several images of each person.
In exchange, Van Gogh gave the Roulin's one painting for each family member.
As the Roulin family was similar in size to Van Gogh's own, in his psychological approach Lubin suggested that Van Gogh may have adopted them as a substitute.