'Electrifying' missive written by artists on pages of French exercise books goes on sale in Paris next month

The handwritten letter, penned jointly by Vincent van Gogh and Paul Gauguin on cheap paper torn out of a school exercise book, speaks of friendship and hope. Written at a critical point in the careers of both men, it refers to dreams of founding a utopian community of brother artists, of a new artistic renaissance, and of paintings now recognised as masterpieces.

The reality was to be less idyllic. Shortly after the missive was sent, the pair quarrelled violently and in one of history's most notorious acts of self-mutilation, Van Gogh sliced off his right ear. It was an act that marked the Dutchman's final decline into madness and suicide.

Now, the four-page letter signed by both artists has emerged from a private collection before its auction in Paris next month, where it is expected to fetch up to €500,000 (£405,000).

Thomas Venning, an expert with the auction house Christie's, said the document offered an insight into the "most famous artistic menage in history".

"I spend my life dealing with letters and this is one of the greatest, most electrifying I have ever seen," he said. "It takes you into their house, into their lives at this particular moment.

"You can imagine Van Gogh sitting down to write the letter on cheap paper because they didn't have much money, then saying to Gauguin: 'You finish it off'."

The letter is written on the square-ruled paper of French exercise books and addressed to Emile Bernard, a young avant garde artist who inspired both men. It was composed in November 1888 at Arles in Provence, where Van Gogh had rented two floors of a private house, 2 Place Lamartine, the subject of the painting La Maison Jaune.

The previous week, after months of procrastination, Gauguin had arrived to live and paint with Van Gogh for one or two years. At the time, the French art world was moving from impressionism to modernism and surrealism, but Van Gogh and Gauguin had yet to be widely recognised.

Van Gogh, mentally fragile and prone to violent mood swings, was fired up with childlike excitement. In the letter, he gives his first impressions of the French painter.

"Gauguin interests me much as a man – very much – I have long thought that in our dirty profession as painters we have the greatest need of people with the hands and stomachs of a labourer – and more natural tastes – more amorous and benevolent temperaments – than the decadent and exhausted Parisian boulevardier.

"Now here without the slightest doubt we are in the presence of a virgin creature with the instincts of a wild animal. In Gauguin, blood and sex prevail over ambition."

He adds: "We have made several excursions to the brothels and it's likely that we will end up working there often. Gauguin has at the moment a painting under way of same night café that I also painted, but with figures seen in the brothels. It promises to become a beautiful thing.

"I've made two studies of falling leaves in an avenue of poplars and a third study of this whole avenue, entirely yellow." [Les Alyscamps.]"

Van Gogh writes that he and Gauguin are discussing "the terrific subject of an association of certain painters" and of his "presentiment of a new world … and a great artistic renaissance" that will find its home in the tropics.

On the final page, Gauguin adds: "Don't listen to Vincent, as you know he's prone to admiration and ditto indulgence. His idea about the future of a new generation in the tropics seems absolutely right to me as a painter, and I still intend to return there when I have the means to do so. Who knows, with a bit of luck …?"

Eight weeks later, on 23 December, the partnership came to a violent end when the pair quarrelled violently over, it is believed, Van Gogh spending the meagre household budget on prostitutes, and his refusal to stop drinking absinthe.

Van Gogh threatened his "friend" with a razor before slicing off his own ear. Shortly afterwards he entered the first of a series of asylums and died in 1890 aged 37 after shooting himself.

Gauguin returned to Paris and later set up a studio in French Polynesia where he died in 1903, aged 54. The pair never met again, though they subsequently corresponded.

Venning says the letter reveals the two men's different characters, and the calm before the storm in their relationship.

"It's a moment of friendship, optimism and shared work. It looks like everything is going to be OK and they achieved a lot of work in a short period of time."

He added: "The dramatic events that followed the writing of this letter make it rather sad. It's a mind blowing document."

The letter is part of the Pierre Berès Collection, being sold at Christie's Paris on 12-13 December.