What algorithm does the Wavelength node use?

Hey, nice you got it to work! Keep in mind that there’s a node version of the script available here, which means GPU rendering is available. And for what it’s worth: I also optimized many of the metals you have listed to be as close to a spectral rendition as possible, when illuminated with white light. The blend file available in the linked post contains all of them, and many more materials.

Cheers!