Series E was introduced subsequently. The banknotes for this issue were bilingual, featuring the bank's name both in Spanish and English. Early specimens for Series F were produced in 1907, but they never reached circulation. The bills for this issue featured the profiles of Christopher Columbus and Juan Ponce de León. The colonial government intended to eliminate all Spanish captions from these notes, intending to accelerate a failed "Americanization" process in Puerto Rico. Series F ultimately entered circulation on July 1, 1909, still featuring bilingual captions and exhibiting a higher degree of technical quality. In 1913, the charter granted by Spain expired and the bank was closed and its assets were liquidated. After this date, Puerto Rico's economy was fully integrated into the United States' currency system, while Puerto Rican dollars were redeemed for United States dollars. Banknotes valorized in millions continued in circulation, thus a collect was ordered and held between January 16 – 24, 1916. The remaining bills, with an estimated value of $14,872 were taken out of circulation nine years later by the Puerto Rico Commercial Bank.