“Deep in the dark pocket of the scientist, the radium broke the gloom with an unending, eerie glow.” 

The Prologue immediately introduces radium and characterizes it as menacing and spooky. As early as 1901, 16 years before Chapter 1 takes place, radium is suspected to be dangerous. The “dark pocket” is significant, too, as it foreshadows that radium will do harm “in the dark”—in the bodies of those who are exposed to it—unseen from the outside. 

"What she did feel part of, though, was radium's all-pervasive entry into American life. It was a craze, no other word for it. The element was dubbed 'liquid sunshine,' and it lit up not just the hospitals and drawing rooms of America, but its theaters, music halls, grocery stores, and bookshelves." 

When Katherine started working at the factory in 1917, radium was widely viewed as wonder drug and cure-all. Its intriguing shine was visually captivating, and it was viewed with awe and optimism. It spoke to America’s technological optimism, a belief that science would improve life for all.

“The dial-painters, dressed in white summer dresses and wide-brimmed hats, would eat ice-cream cones while sitting on the narrow makeshift bridge that lay across the brook by the studio, swinging their legs or holding on to one another as they tried not to fall in the water.” 

This passage characterizes the girls’ fun, happy attitude towards their work at the dial-painting studio. Their white outfits might symbolize innocence, and their ice-cream cones complete the image of young, carefree people enjoying their time at work. Despite this happy image, the reader already knows that radium will gravely harm the girls, which gives the scene an eerie quality.