“For the Trinity explosion, the special effects crew, led by Scott R. Fisher, employed a traditional technique
known as Forced Perspective, using scaled-down models. However, Fisher proudly referred to these models as "big-atures" instead of miniatures, as they were made as large as possible while maintaining manageable proportions. The trick is simple: the closer these props were positioned to the camera, the larger they appeared, effectively conveying the desired visual impact.”
“Following the prop sets, the intense fire during the explosion was an amalgamation primarily of gasoline and propane. According to Fisher, this combination was chosen due to its high energy output in terms of the pyrotechnic aspect. The addition of aluminum powder and magnesium aimed to recreate the blinding flash commonly associated with a nuclear explosion. The team's intention was to create a visually striking effect that would leave a lasting impression on the audience, akin to the brightness experienced during an actual nuclear event. Their ultimate objective was to captivate viewers with this remarkable display and stimulate discussions surrounding it.”
“However, the biggest challenge was to create the mushroom cloud infamous for mammoth explosions. “Mushroom cloud” is a typical layman's term used to describe the quintessential by-product of a nuclear detonation. In a conversation with Empire, Nolan revealed that visualizing the fiery abstractness within Oppenheimer's brilliant mind is an insurmountable challenge. To achieve that veracity, palpability, and tactile explosion of the Trinity, the crew sagaciously photographed the whole explosion created by TNT in a multifaceted viewpoint and did compositing using computers which enabled the team to add multi-layers to the explosion. In a way, Nolan actually
set off a bomb, but it's not an actual nuclear bomb.”