From top to bottom: (1) Ni I synthetic spectrum (red) at the orbital conditions of Hyakutake, (2) Fe I synthetic spectrum (black) at the orbital conditions of Hyakutake, (3) laboratory spectrum of an Ni/Fe probe at 3 cm depth in the CTH plasma apparatus (shot 18,112,918, frame 88, green) and laboratory spectrum of an Au/Ni/Fe probe at 6 cm depth in the CTH plasma apparatus (shot 18113013, frame 81, purple), (4) observation spectrum of Hyakutake (blue). Ni I (red) and Fe I (black) lines identified in the comet spectrum are indicated by vertical dashed lines in the lab and comet spectra.