NEW YORK (AP) – A never-before exhibited collection of letters from Vincent van Gogh to a friend reveal the artistic genius’s daily life – from his beliefs about sex to how he put the wrong postage stamp on a letter.

“You see the human being in a body – who gets exhausted, working at his easel, outdoors in the blazing sun, with no food on some days,” says Jennifer Tonkovich, curator of “Painted With Words: Vincent van Gogh’s Letters to Emile Bernard,” on display at The Morgan Library & Museum.

The 20 letters – alternately frank, humorous and profound – relate to 22 paintings, drawings and watercolors in the exhibit that the two artists discussed or exchanged, including a portrait of a French soldier dressed in a bright uniform influenced by the Algerian background of the so-called Zouave regiment.

“It’s coloristically brilliant. And it captures the humanity of the moment,” said Tonkovich of the face that the artist describes as “bloody ugly.”

Van Gogh wrote the letters over two years starting in 1887.

Bernard, an artist and poet 15 years younger, became friends with the Dutch-born van Gogh in Paris and the two often worked by side. Van Gogh later moved to Arles, in the south of France. Deeply depressed, he committed suicide in 1890 at 37, walking into fields in Auvers-sur-Oise outside Paris and shooting himself in the chest.

Months earlier, from Arles, he had written to Bernard: “I am in better health here than in the north – I even work in the wheat fields at midday, in the full heat of the sun, without any shade whatever, and there you are, I revel in it like a cicada.”

In the 1920s, the letters ended up in the possession of the Baroness Marianne de Goldschmidt-Rothschild, who kept them in her home in Berlin and then passed them on to her descendants in Paris. Nineteen of the letters now belong to collectors Eugene and Clare Thaw, of Santa Fe, N.M., who have promised the letter collection worth millions to the museum.

The letters from Bernard to van Gogh have disappeared, perhaps because van Gogh moved around while being treated at various psychiatric clinics, said Tonkovich.

She said the letters debunk the popular assumption that the artist was an unknown, naive genius recognized only after his death. “You have the sense of a well-read person; van Gogh read everything from the Bible to Zola. And his talent was recognized even then.”

Perhaps the most fascinating aspect of the correspondence are details of daily life. Van Gogh complains about his eyes getting tired from painting, and about the challenge of keeping his easel from being blown away by the wind in the fields.

And he talks about sex.

“Van Gogh adamantly believed that too much sexual activity detracts from your work,” said the curator. “He believed sexual activity depletes you.”

Tonkovich said the artist had left a woman he was living with in Holland to devote himself entirely to painting. However, when he had the money, van Gogh said he tried to visit a brothel about every two weeks.

In the letters, he talks about finances and about his health – and how to maintain his stamina for work by eating well.

There’s little direct reference to his mental health, “but you’re aware that there’s this problem. He talks about calming his head,” says the curator.

The exhibit – the largest collection of van Gogh letters outside the van Gogh Museum in Amsterdam – opens to the public on Friday and runs through Jan. 6.