Question: In what year was the Blue period of Picasso?
About the article "Pablo Picasso", section "Blue Period".

Candidate passages:
At the time, having renounced his classical and traditional education and searching for fame, Picasso and his friend Carlos Casagemas moved to Paris.
A year later, Casagemas became hopelessly miserable from a failed love affair and committed suicide.
Picasso was greatly afflicted by this event and was soon depressed and desolate.
In addition, Picasso was very poor.
His poverty made him identify and relate to beggars, prostitutes and other downtrodden outcasts in society.
These events and circumstances were the impetus for the beginning of Picasso’s Blue Period which lasted from 1901 to 1904.
The Blue Period is identified by the flat expanses of blues, greys and blacks, melancholy figures lost in contemplation, and a deep and significant tragedy.
After the Blue Period came Picasso's Rose Period, and eventually the Cubism movement which Picasso co-founded. 
The Blue Period () is a term used to define the works produced by Spanish painter Pablo Picasso between 1901 and 1904 when he painted essentially monochromatic paintings in shades of blue and blue-green, only occasionally warmed by other colors.
These somber works, inspired by Spain and painted in Barcelona and Paris, are now some of his most popular works, although he had difficulty selling them at the time.
This period's starting point is uncertain; it may have begun in Spain in the spring of 1901 or in Paris in the second half of the year.
In choosing austere color and sometimes doleful subject matter—prostitutes, beggars and drunks are frequent subjects—Picasso was influenced by a journey through Spain and by the suicide of his friend; Carlos Casagemas took his life at the L’Hippodrome Café in Paris, France by shooting himself in the right temple on February 17, 1901.
Although Picasso himself later recalled, "I started painting in blue when I learned of Casagemas's death", art historian Hélène Seckel has written: "While we might be right to retain this psychologizing justification, we ought not lose sight of the chronology of events: Picasso was not there when Casagemas committed suicide in Paris ...
When Picasso returned to Paris in May, he stayed in the studio of his departed friend, where he worked for several more weeks to prepare his exhibition for Vollard".
The works Picasso painted for his show at Ambroise Vollard's gallery that summer were generally characterized by a "dazzling palette and exuberant subject matter".
Picasso's psychological state worsened as 1901 continued.
In the latter part of 1901, Picasso sank into a severe depressionand blue tones began to dominate his paintings.
Picasso's painting "La mort de Casagemas", completed early in the year following his friend's suicide, was done in hot, bright hues.
The painting considered the first of his Blue Period, "Casagemas in His Coffin", was completed later in 1901 when Picasso was sinking into a major depression.
Picasso, normally an outgoing socializer, withdrew from his friends.
Picasso's bout of depression was to last several years.
Picasso's career had been promising before 1901 and early in that year he was making "a splash" in Paris.
However, as he moved towards subject matter such as society's poor and outcast, and accented this with a cool, anguished mood with blue hues, the critics and the public turned away from his works.
Members of the public were uninterested in displaying the Blue Period works in their homes.
Picasso continued his output, but his financial situation suffered:From 1901 to 1903, he painted several posthumous portraits of Casagemas, culminating in the gloomy allegorical painting "La Vie", painted in 1903 and now in the Cleveland Museum of Art.
The same mood pervades the well-known etching "The Frugal Repast" (1904) which depicts a blind man and a sighted woman, both emaciated, seated at a nearly bare table.
Blindness is a recurrent theme in Picasso's works of this period, also represented in "The Blindman's Meal" (1903, the Metropolitan Museum of Art) and in the portrait of "Celestina" (1903).
Other frequent subjects include female nudes and mothers with children.
Solitary figures dominate his Blue Period works.
Themes of loneliness, poverty and despair pervade the works as well.
Possibly his most well known work from this period is "The Old Guitarist."
Other major works include "Portrait of Soler" (1903) and "Las dos hermanas" (1904).
Picasso's Blue Period was followed by his Rose Period.
Picasso's bout with depression gradually ended, and as his psychological state improved, he moved towards more joyful, vibrant works, and emphasized the use of pinks ("rose" in French) and other warm hues to express the shift in mood and subject matter.
The painting "Portrait of Suzanne Bloch" (1904), one of the final works from this period, was stolen from the São Paulo Museum of Art (MASP) on December 20, 2007, but retrieved on January 8, 2008. 
Works 1935–1959.
Early works.
In 1935 Picasso's wife Olga Khokhlova left him.
That summer, rather than leave Paris as was his custom, Picasso stayed home, withdrawing to the relative isolation of le Château de Boisgeloup in Gisors that autumn.
According to friend and biographer Roland Penrose, at first: "Picasso let no one know what he was jotting down in the little note-books that he hid as soon as anyone came in the room.
"Some of Picasso's first poetical explorations involved the application of coloured blobs to represent objects.
He gave up this approach to focus upon words and his early attempts employed a strong use of visual images and his own method of using dashes of differing lengths to break the text.
Picasso quickly abandoned punctuation altogether, explaining to Braque:"Punctuation is a cache-sexe which hides the private parts of literature.
"In a 1935 letter to her son, Picasso's mother said: "...
They tell me that you write.
I can believe anything of you.
If one day they tell me that you say mass, I shall believe it just the same."
That same year, André Breton wrote about Picasso's poetry for the French artistic and literary journal "Cahiers d' Art", wherein Breton exclaimed that: "Whole pages appear in bright variegated hues like a parrots' feathers."
Penrose describes how in the following fragment, "..words have been applied as a painter uses colour from his brush.
":listen in your childhood to the hour that white in the blue memory borders white in her very blue eyes and piece of indigo of sky of silver the white white traverse cobalt the white paper that the blue ink tears out blueish its ultramarine descends that white enjoys blue repose agitated in the dark green wall green that writes its pleasure pale green rain that swims yellow green...-Excerpt from early Picasso poem.
Over a six-week period in the spring of 1936, Picasso sent a series of letters to his "closest confidant and devoted friend" poet and artist Jaime Sabartés.
Penrose notes that: "such frequent letter-writing was so unusual as to be disquieting, and a certain sign of restlessness."
On 23 April, Picasso wrote to Sabartés announcing that: "from this evening, I am giving up painting, sculpture, engraving, and poetry so as to consecrate myself entirely to singing."
However, four days later Picasso wrote: "I continue to work in spite of singing and all.
"As is the case with his paintings, Picasso's poetry can be read and interpreted in numerous ways.
The majority of his poems are untitled, apart from the odd mention of time and place, solely the dates are given.
Sabartés recalled how: "Speaking about his writings, he always tells me that what he wants is not to tell stories or to describe sensations, but to produce them with the sound of the words; not to use them as a means of expression but to let them speak for themselves as he does sometimes with colours.." 
Picasso's African Period, which lasted from 1906 to 1909, was the period when Pablo Picasso painted in a style which was strongly influenced by African sculpture.
This proto-Cubist period following Picasso's Blue Period and Rose Period has also been called the Negro Period, or Black Period. 
Picasso's Blue Period (1901–1904), characterized by somber paintings rendered in shades of blue and blue-green, only occasionally warmed by other colours, began either in Spain in early 1901, or in Paris in the second half of the year.
Many paintings of gaunt mothers with children date from the Blue Period, during which Picasso divided his time between Barcelona and Paris.
In his austere use of color and sometimes doleful subject matter – prostitutes and beggars are frequent subjects – Picasso was influenced by a trip through Spain and by the suicide of his friend Carlos Casagemas.
Starting in autumn of 1901 he painted several posthumous portraits of Casagemas, culminating in the gloomy allegorical painting "La Vie" (1903), now in the Cleveland Museum of Art.
The same mood pervades the well-known etching "The Frugal Repast" (1904), which depicts a blind man and a sighted woman, both emaciated, seated at a nearly bare table.
Blindness is a recurrent theme in Picasso's works of this period, also represented in "The Blindman's Meal" (1903, the Metropolitan Museum of Art) and in the portrait of "Celestina" (1903).
Other works include "Portrait of Soler" and "Portrait of Suzanne Bloch".