The best rule for printing is to not go lower that 300 pixels/inch, so in your case with a 12k resolution you could print up to 40 inches on the wide dimension… but you may want to pixel peep to see if you are happy to that size. But having said that, modern printing methods can achieve better resolution and you may start seeing little noisy details (if any - I haven’t pixel peeped your image even though I gave it a “like” the other day) if you try for the 40” size.
I’ve printed a few items on metal, and it would be interesting to see the difference between direct metal printing versus white flood layer (printing a white base onto the metal before applying the image). The white flood layer will show the work in any light (it’s like printing on high quality paper), but the direct to metal printing needs reflectance to see the image - and when there is reflectance, the effect is really nice. I have a M31 on metal on display in a room with a lot of natural light and love it during daylight hours, but in the evening it goes really dull, and the neighboring Pacman (printed on white flood layer on the metal) starts to steal the show.
Another note - I just printed a Rosette onto white-flooded metal. I was disappointed in the light blue oxygen highlights - they became very blanched and lost a lot of saturation, I believe because the company auto-scaled the luminance. If possible, see if the printer will give you a proof prior to printing. For a lot of these online portals where you can order metal prints, it’s a pretty automated process and you may not have the proof option. But a phone call to express your concerns - if they are a real printhouse - will help them get the project the way you want it. I just feel that many astrophotos might be subject to autoscaling the output since any top ends in the histograms are little pinpoints and probably really don’t register a lot of weight in their software and your histogram goes heavily light - especially your gorgeous starless nebulosity - the printer will really have to focus on keeping faithful to the histogram.
Worst case - maybe they can print the job on high quality paper, maybe half-sized to your intended finish size before you commit to a larger investment in full-size metal.
EDIT: Okay, I’ve now pixel peeped your image. When I zoom in to your AB image, to 0.13x zoom, that presents 100 dpi on my screen. Zooming to 0.39x, that shows me the detail at a virtual 300dpi, and I feel your image holds up nicely. It seems the dusty fingers still have some sharpness at that level (which would be equivalent to someone getting within 12” of your print, if done at 20” wide, 18” away if done at 30” wide).
Whatever you decide, I think the image will be a conversation piece…. just don’t get into the ‘green’ discussion ;-)
CS,
Mark
