Incorruptible
One of the key thematic elements in the novel is the potential for anyone to be corrupted. The flaws of flesh are juxtaposed against the silver which is so integral to the narrative. "And silver is an incorruptible metal that can be trusted to keep its value for ever. . . . An incorruptible metal." The imagery seeks to connect the inability of silver to be tarnished with the inevitability of mankind to be tarnished by greed.
Characterization
Imagery is especially effective in this book for characterization purposes. "Mrs. Gould, with her little head and shining coils of hair, sitting in a cloud of muslin and lace before a slender mahogany table, resembled a fairy posed lightly before dainty philtres dispensed out of vessels of silver and porcelain." The imagery used to describe the wife of a man falling under the sway of greed could easily enough have been conveyed simply by telling. This precisely detailed description is much more effective at portraying her increasing fragility in the face of her husband's spiraling lack of humanity. The use of words like "little" and "dainty" combined with the comparison to a fairy all contribute to this portrait.
Nostromo
Nostromo is a man held in the highest esteem as being incorruptibility in the flesh. A series of events lead him to be tested and it begins with the discovery of four missing bars of silver. "He sat down on the soft earth, unresisting, as if he had been chained to the treasure, his drawn-up legs clasped in his hands with an air of hopeless submission, like a slave set on guard." This is the image of Nostromo at the moment of truth. The description of being held prisoner to an absurd wealth of silver nobody else on earth knows still exists is filled with irony. The imagery here is that of a man with nothing to live for. And yet it is the image of man sitting on treasure trove only he knows is available for the taking.
The Lighthouse
The building of a lighthouse plays a significant role in the arc of Nostromo from incorruptible to corrupted. "The sun sank almost to the edge of a purple ocean; and the white lighthouse, livid against the background of clouds filling the head of the gulf, bore the lantern red and glowing, like a live ember kindled by the fire of the sky." This sentence is almost nothing but imagery and it works mostly on a symbolic level. The sinking of the sun is representative of the sun setting on Nostromo's story. The color of the lighthouse is notable for the resonance of innocence juxtaposed with its description of being "livid" against the clouds. The imagery in this description appeals mostly to the visual sense of the reader, but the concrete qualities of the colorful descriptions work on a symbolic level that inevitably connects it to Nostromo's fate.
