Question: When was the painting put in the hidden room?
About the article "Portrait of Dr. Gachet", section "Original version".

Candidate passages:
Original version.
First sold in 1897 by Van Gogh's sister-in-law for 300 francs, the painting was subsequently bought by Paul Cassirer (1904), Kessler (1904), and Druet (1910).
In 1911, the painting was acquired by the Städel (Städtische Galerie) in Frankfurt, Germany and hung there until 1933, when the painting was put in a hidden room.
The Reich Ministry of Public Enlightenment and Propaganda confiscated the work in 1937 as part of its campaign to rid Germany of so-called degenerate art, leading to Hermann Göring hurriedly selling it to a dealer in Amsterdam.
The dealer in turn sold it to collector Siegfried Kramarsky, who brought it with him when he fled to New York, where the work was often lent to the Metropolitan Museum of Art.
Kramarsky's family put the painting up for auction at Christie's New York on May 15, 1990, where it became famous for Ryoei Saito, honorary chairman of Daishowa Paper Manufacturing Co., paying US$82.5 million for it, making it then the world's most expensive painting.
Remarkably, two days later Saito would buy Renoir's Bal du moulin de la Galette for a nearly-as-much $78.1 million at Sotheby's.
The 75-year old Japanese businessman briefly caused a scandal when he said he would have the Van Gogh painting cremated with him after his death, though his aides later claimed Saito threatening to torch the masterpiece was just an expression of intense affection for it.
Though he later said he would consider giving the painting to the Japanese government or a museum, no information has been made public about the exact location and ownership of the portrait since his death in 1996.
Reports in 2007 have claimed the painting was sold a decade earlier to the Austrian-born investment fund manager Wolfgang Flöttl.
Flöttl, in turn, had reportedly been forced by financial reversals to sell the painting to parties as yet unknown.
Matejko began work on the painting in the middle of January 1891, to coincide with the centenary of the Constitution.
Although the painting was not finished until October, by May 3 it was sufficiently advanced to be shown at the anniversary exhibition in Sukiennice, Kraków.
On April 7, 1892, Matejko transferred the painting to Prince Eustachy Stanisław Sanguszko, marshal of Galician Sejm in Lwów, and it was displayed in the Sejm building (now the main building of the Lviv University).
This painting was one of the last works by Matejko, who died in November 1893.
In 1920, two years after Poland regained independence, the painting was moved to Kraków, where from 1923 it was displayed in the building of the Polish Sejm.
The painting was hidden by the Polish resistance during World War II, when Poland was occupied by the Germans.
After the war the painting was transferred to the National Museum in Warsaw, and occasionally displayed in the Sejm building.
Since 1984 the painting has been in the collection of the Royal Castle in Warsaw, where Matejko himself declared he would like the painting to be shown.
The painting is displayed in the anteroom of the Chamber of Senators, where the Constitution was adopted.
The painting was restored in 2007. 
The "Portrait of the Duchess of Alba" was painted in 1797 by Spanish painter Francisco José de Goya y Lucientes.
The work is kept at the New York Hispanic Society, owned and operated by the Hispanic Society of America.
In the painting, the duchess (María Cayetana de Silva, 13th Duchess of Alba) is thirty-five years old, and her husband had died the year before, so she is dressed in mourning clothes (attire).
In the painting, she is pointing to the ground, where the words "solo Goya" are lightly engraved.
She is wearing two rings, one engraved with the word "Alba", the other engraved with "Goya".
The inscription of the word "solo" was initially hidden, but after the painting was restored the word was revealed.
This work is among a number Goya painted of the duchess.
When she retreated to a residence after her husband died a year earlier for a period of mourning, Goya followed and created numerous paintings and sketches of the duchess during her stay.
One day, the duchess walked into Goya's studio and requested that he put on the duchess' makeup, then create a painting for her, which he did.
This painting is the "Portrait of the Duchess of Alba", painted at her request. 
The process repeated with a second hidden pictures round and set of rooms to search.
The dollar values increased to $75 for finding a correct hidden picture and $100 for successfully finding a hidden object in a room.
One of the rooms in round two was the "Instant Prize Room".
If the team found the hidden object in the Instant Prize Room (which was never revealed until a team entered it), they won a bonus prize in addition to the $100 for finding the hidden object.
If not, the prize went unclaimed and the opposing team was awarded the $100.
Whichever team had the most money after the last room was played won the game and advanced to the Room to Room Romp. 
"The Night Watch" first hung in the "Groote Zaal" (Great Hall) or Amsterdam's "Kloveniersdoelen".
This structure currently houses the Doelen Hotel.
In 1715, the painting was moved to the Amsterdam Town Hall, for which it was altered.
When Napoleon occupied the Netherlands, the Town Hall became the Palace on the Dam and the magistrates moved the painting to the "Trippenhuis" of the family Trip.
Napoleon ordered it returned, but after the occupation ended in 1813, the painting again went to the "Trippenhuis", which now housed the Dutch Academy of Sciences.
It moved to the new "Rijksmuseum" when its building was finished in 1885.
The painting was removed from the museum in September 1939, at the onset of World War II.
The canvas was detached from its frame and rolled around a cylinder.
The rolled painting was stored in Radboud Castle in Medemblik, north of Amsterdam.
After the end of the war, the canvas was re-mounted, restored, and returned to its rightful place in the Rijksmuseum.
On December 11, 2003, "The Night Watch" started its move to a temporary location, due to a major refurbishment of the Rijksmuseum.
The painting was detached from its frame, wrapped in stain-free paper, put into a wooden frame which was put into two sleeves, driven on a cart to its new destination, hoisted, and brought into its new home through a special slit.
While the refurbishment took place, "The Night Watch" could be viewed in its temporary location in the "Philipsvleugel" of the Rijksmuseum.
When the refurbishment was finished in April 2013, the painting was returned to its original place in the "Nachtwachtzaal" ("Room of the Night Watch").