Question: What was Picasso's most mysterious and challenging painting and when was it created?
About the article "Dora Maar au Chat", section "Descriptions of painting".

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The Rose Period comes from the time when the style of Pablo Picasso's painting used cheerful orange and pink colours in contrast to the cool, somber tones of the previous Blue Period.
The Rose Period lasted from 1904 to 1906.
Picasso was happy in his relationship with Fernande Olivier whom he had met in 1904 and this has been suggested as one of the possible reasons he changed his style of painting.
Harlequins, circus performers and clowns appear frequently in the Rose Period and populated Picasso's paintings at various stages throughout the rest of his long career.
The harlequin, a comedic character usually depicted in checkered patterned clothing, became a personal symbol for Picasso.
The Rose Period has been considered French influenced, while the Blue Period more Spanish influenced, although both styles emerged while Picasso was living in Paris.
Picasso's Blue Period began in late 1901, following the death of his friend Carlos Casagemas and the onset of a bout of major depression.
It lasted until 1904, when Picasso's psychological condition improved.
The Rose Period is named after Picasso's heavy use of pink tones in his works from this period, from the French word for pink, which is "rose".
Picasso's highest selling painting, "Garçon à la pipe (Boy with a pipe)" was painted during the Rose Period.
Other significant Rose Period works include: "Woman in a Chemise (Madeleine)" (1904–05), "The Actor" (1904–1905), "Lady with a Fan" (1905), "Two Youths" (1905), "Harlequin Family" (1905), "Harlequin's Family With an Ape" (1905), "La famille de saltimbanques" (1905), "Boy with a Dog" (1905), "Nude Boy" (1906), "Boy Leading a Horse" (1906), and "The Girl with a Goat" (1906).
The Rose Period was followed by Picasso's African influenced period, where his Proto-Cubist work took form.
The most famous painting from Picasso's African Period is Les Demoiselles d'Avignon, painted in 1907, which created a sensation among critics and the public when it was exhibited in 1916. 
The painting was acquired in 1907 by Josef Stránský, an art dealer and a friend of Picasso's.
From 1945 to 1962, the painting was owned by Picasso's son Paulo Picasso.
The painting was owned by Joan Whitney Payson, and it was consigned by her daughter, Lorinda de Roulet.
The painting was owned by the Swedish investment banker and mecenat Fredrik Roos when it was sold at Binoche et Godeau in Paris on November 30, 1989.
The buyer, Tomonori Tsurumaki, a real-estate developer, investment banker and owner of Autopolis racetrack, purchased the painting for the sum of $51,670,000, making it one of the world's most expensive paintings.
With the collapse of Tsurumaki's company, Nippon Tri-Trust, the painting ended up in the hands of the construction company Hazama, which had constructed Tsurumaki's racetrack.
Hazama, having run into financial difficulties, put the painting up as collateral when the firm took a loan from Lake Credit Company.
Thus, Lake Credit Company came into possession of " Les Noces de Pierrette".
When Lake Credit Company sold its stake in the mainline consumer loan business to GE Capital, " Les Noces de Pierrette" (along with 500 other paintings worth approximately $200 million) became the property of GE Capital.
Presently, "Les Noces de Pierrette" is secured in the vault of Mitsui Trust Bank. 
La Lecture (or Reading) is a painting by Spanish artist Pablo Picasso completed in January 1932.
The oil painting depicts Picasso's mistress and muse, Marie-Thérèse Walter, asleep with a book upon her lap.
The painting led to the breakup of Picasso's marriage to Olga Khokhlova after she saw it at a retrospective exhibition and realised that the facial features were not her own.
The painting went to auction in 1989 and in 1996, where it failed to sell.
In January 2011, it was announced that "La Lecture" would be going to auction on 8 February.
The painting, which had not been seen in Europe since the exhibition, was then displayed at Sotheby's in Paris. 
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. 
During the first half of 20th Century many leading Spanish artists were working in Paris, where they contributed to - and sometimes led - developments in the Modernist art movement.
As perhaps the most important example of this, Picasso, working together with the French artist Braque, created the concepts of Cubism; and the sub-movement of Synthetic Cubism has been judged to have found its purest expression in the paintings and collages of Madrid-born Juan Gris.
In a similar way, Salvador Dalí became a central figure of the Surrealist movement in Paris; and Joan Miró was influential in abstract art.
Picasso's Blue Period (1901–1904),which consisted of somber, blue-tinted paintings was influenced by a trip through Spain.
The Museu Picasso in Barcelona features many of Picasso's early works, created while he was living in Spain, as well as the extensive collection of Jaime Sabartés, Picasso's close friend from his Barcelona days who, for many years, was Picasso's personal secretary.
There are many precise and detailed figure studies done in his youth under his father's tutelage, as well as rarely seen works from his old age that clearly demonstrate Picasso's firm grounding in classical techniques.
Picasso presented the most durable homage to Velázquez in 1957 when he recreated Las Meninas in his characteristically cubist form.
While Picasso was worried that if he copied Velázquez's painting, it would be seen only as a copy and not as any sort of unique representation, he proceeded to do so, and the enormous work—the largest he had produced since Guernica in 1937—earned a position of relevance in the Spanish canon of art.
Málaga, Picasso's birthplace, houses two museums with significant collections, the Museo Picasso Málaga and Birthplace Museum.
Salvador Dalí was a central artist within the Surrealist movement in Paris.
Although Dalí was criticized for accommodating Franco's regime, André Breton, the Surrealist leader and poet, asked him to represent Spain at the 1959 Homage to Surrealism Exhibition which celebrated the fortieth anniversary of Surrealism.
In line with the Surrealist movement's objectives, Dalí stated that his artistic aim was that ""...the world of imagination and of concrete irrationality may be as objectively evident ... as that of the exterior world"...", and this goal can be seen in his most familiar painting, The Persistence of Memory.
Here he paints with a precise, realistic style, based on studies of Dutch and Spanish masters, but with a subject that dissolves the boundaries between organic and mechanical and is more akin to the nightmarish scenes of the Netherlandish painter Hieronymus Bosch, whose "Garden of Earthly Delights" provided the model for the central, sleeping figure of Dalí's work.
Joan Miró was also closely associated with the Surrealists in Paris, who particularly approved of his use of automatism in composition and execution,designed to expose the subconscious mind.
Although his later and more popular paintings are refined, whimsical and apparently effortless, his influential period in the 1920s and 1930s produced works that were provocative in their sexual symbolism and imagery, and employing rough, experimental materials, including sandpaper, unsized canvases, and collage.
In mature period painting, "La Leçon de Ski", his characteristic language of signs, figures and black linear forms against more textured and painterly background is evident.
Ignacio Zuloaga and José Gutiérrez Solana were other significant painters of the first half of 20th century.