Kodak™ "High Speed Black and White Infra Red" film was a curious medium.
You could never tell how much infra red light was around to properly expose it. Unlike normal film, it had to be loaded and unloaded in total darkness. It was so sensitive to daylight that even using a changing bag was risky; as was changing lenses! So having more than one Nikon FM2 pre loaded with the film helped.
My technique involved the combined use of two filters - a red (W25) and a polariser. You had to add the filters once you’d framed the subject, as you couldn't see anything in the view finder with them on the lens. Starting from a base exposure (experience and guesswork) you then bracketed 2 stops either side and hoped for the best.
The resulting image is from an invisible wavelength, 900nm, in effect a scene that we can't actually see - weird!