"The air was dark above Gravesend, and the father back still seemed condensed into a mournful gloom brooding motionless over the biggest, and the greatest, town on earth." 

The narrator makes this observation of London from his seat aboard the Nellie at the beginning of the text. Right away, Conrad offers a paradoxical image to foreshadow the novella’s ultimate discussion of imperialism’s darkness. London, despite being the “greatest town on earth,” appears blanketed in a dark and sorrowful mood, one which speaks to its position as the center of the world’s largest colonial empire. Conrad’s choice to use a word like “greatest” which has a distinctly positive connotation heightens the sense of paradox in this image and calls London’s assumed grandeur into question.

"Then I noticed a small sketch in oils, on a panel, representing a woman draped and blindfolded carrying a lighted torch. The background was sombre—almost black. The movement of the woman was stately, and the effect of the torchlight on the face was sinister." 

Marlow spots this painting, created by Kurtz, in the main building of the Central Station as he speaks to the Brickmaker. The imagery in this symbolic sketch highlights the evil that lurks behind Europe’s self-proclaimed civilizing missions. With an allusion to the light and dark motif that occurs throughout the novella, the general image of a torch against a background of darkness speaks to notions of white saviorism, or the belief that Europeans would enlighten the people of Africa. More nuanced details, however, appear to challenge the positive connotation of traditional light-in-darkness imagery. The fact that the woman is blindfolded speaks to European ignorance or rejection of the truth behind their imperial pursuits, and the sinister shadowing of the torchlight emphasizes the evil inherent in white saviorism.  

"There were no practical hints to interrupt the magic current of phrases, unless a kind of note at the foot of the last page, scrawled evidently much later, in an unsteady hand, may be regarded as the exposition of a method. It was very simple, and at the end of that moving appeal to every altruistic sentiment it blazed at you, luminous and terrifying, like a flash of lightning in a serene sky: ‘Exterminate all the brutes!’"

As Marlow reads the pamphlet Kurtz wrote on behalf of the International Society for the Suppression of Savage Customs, he comes across this violent addendum handwritten on the page. The contrast between the “magic current of phrases” that make up the body of the pamphlet and its final, commanding instruction highlight the ultimate hypocrisy of imperialism. Kurtz almost entrances Marlow with his words, imploring him to identify the Society’s mission as an altruistic one, but in the end, admits that their true goal is genocide.