Quote from Delacroix' letter to Théophile Silvestre, Paris, 31 December 1858; as quoted in Eugene Delacroix – selected letters 1813 – 1863, ed. and translation Jean Stewart, art Works MFA publications, Museum of Fine Art Boston, 2001, p. 352 
1831 - 1863
                                    
        “What surprising fellows those French painters are. A Millet, Delacroix, Corot, Troyon, Daubigny, Rousseau, and a Daumier.... Something else about Delacroix - he had a discussion with a friend about the question of working absolutely from nature, and said on that occasion that one should take one's 'studies' from nature - but that the 'actual painting' had to be made 'by heart'. This friend was walking along the boulevard when they had this discussion - which was already fairly heated. When they parted the other man was still not entirely persuaded. After they parted, Delacroix let him stroll on for a bit - then (making a trumpet of his two hands) bellowed after him in the middle of the street - to the consternation of the worthy passers-by:
'By heart! By heart!”
    
    
    
    
        
        
        
            
            
        
        
        
        
        
        
            (Par coeur! Par coeur!)
I can't tell you how much I enjoyed reading this article and some other things about Delacroix.. 
In his letter to Anthon van Rappard, from Nuenen, The Netherlands, 8 and c. 15 August 1885 - original manuscript, letter 526, at Van Gogh Museum, location Amsterdam - inv. nos. b8390 V/2006,  http://vangoghletters.org/vg/letters/let526/letter.html 
See for this anecdote, taken from Charles Blanc, Les artistes de mon temps, letter 496, n. 7. 
1880s, 1885
        
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Vincent Van Gogh 238
Dutch post-Impressionist painter (1853-1890) 1853–1890Related quotes
Source: Quotes of Paul Cezanne, after 1900, Cézanne, - a Memoir with Conversations, (1897 - 1906), p. 196 in: 'What he told me – II. The Louvre'
                                        
                                        In his letter to Theo, from the Hague, c. 11 July 1883 - original manuscript at Van Gogh Museum, location Amsterdam - inv. nos. b322 a-c V/1962,  http://vangoghletters.org/vg/letters/let361/letter.html 
At the exhibition 'Les cent chefs d'oeuvre' at Galerie Georges Petit - in Paris, 1883 there were 9 paintings of Troyon. Vincent had asked Theo in Paris to give him a description of the works at this exhibition. Vincent already appreciated Troyon's painting style, which he knew from his Paris' years at art-gallery Goupil where he worked 
1880s, 1883
                                    
                                        
                                        In 1957; p. 33 
before 1960, "Yves Klein, 1928 – 1962, Selected Writings"
                                    
                                        
                                        Quote in his letter to brother Theo, from Saint-Rémy-de-Provence, Sept. 1889; as quoted in  Vincent van Gogh, edited by Alfred H. Barr; Museum of Modern Art, New York, 1935 https://www.moma.org/documents/moma_catalogue_1996_300061887.pdf, p. 33  (letter 604) 
1880s, 1889
                                    
Journeys Out of the Body (1971), Chapter 2. Search and Research
Source: 1940's, La mia Vita (1945), Carlo Carrà; as quoted in Futurism, ed. Didier Ottinger (2008), p. 29 - In his quote Carrà is refering to his painting 'The Funeral of the Anarchist Galli', he painted ca 1910/11
As quoted in The Puzzle Instinct : The Meaning of Puzzles in Human Life (2004) by Marcel Danesi, p. 71 from Human All-Too-Human
                                        
                                        remark on his cooperative relation with Jasper Johns, to his biographer Calvin Tomkins 
As quoted in Lives of the great twentieth century artists, Edward Lucie-Smith, London 1986, p. 31 
1980's