I am sort of considering building a relatively large fixture to achieve this effect : https://cozo.co/collections/lighting
I would use these sheets from Home Depot : https://www.homedepot.ca/product/paulin-12-x-24-x-0-20-inch-decorative-aluminum-sheet-copper-elliptical/1000861872
Do you think that a 175 watt metal halide would be too bright for this ? I would use it most likely in a relatively large room (up to half a standard school gymnasium). It would likely be mounted quite high, maybe 8-9 feet above the floor.

Many thanks.

I think it would need something short arc, so the ornaments won't be smeared that much. So a 150W pulse MH, even an CMH?

Makes sense, I didn't think of that. I thought of the 175W because I have lamps and I wouldn't have to deal with ignitors for a remote ballast. If this goes ahead, I'll consider CMH, though.

Could look into the 145w Philips Allstart CMH lamps if you don't want to deal with ignitors for a remote ballast. They run on 175w probe start MH ballasts.

Another option would be a compact CMH setup (think CDM-TC) paired with a small electronic ballast that might fit inside the luminaires to avoid the need for remote ballasting.

Yes, I was thinking of making them smaller. Electronic ballasts being smaller and lighter would be an option.

Also, the Allstart lamps would also be an option. I'll have to think it over.