with 0.13 mm of silver because of plutonium's susceptibility to corrosion in air. This layer, however, developed blisters, which had to be ground off. These gaps were then patched with gold leaf before the test. The Fat Man pit, and those of subsequent models, were all plated with nickel. A hollow pit was considered and known to be more efficient but ultimately rejected due to higher requirements for implosion accuracy.

Later