Take a look at this link:
It may not relate exactly to what your doing but you may find some interesting points. The ‘standing wave in oxide’ I mentioned earlier is from this conversation.
I’m beginning to think the materials and equipment are only half the story, the other half is creativity, execution and presentation. I’m worried about the IR camera as there seems to be a defect in the few pictures I took. There are vertical lines in the images that I fear may come from sensor damage. That’s strange because it came from a respected source.
Other than that I’m not sure if the images will be any more effective for engraving than b/w conversion and using a Colour Polarizing Filter on the nikon d610 to lower the palette and separating the remaining tones for effective contrast, and for you, it’s also about contrasting defined areas of color/tone and…finding and matching power levels and exposure time to achieve a mix of RGB.