I am considering using a 10 inch galvanized bucket as a reflector for a metal halide lamp of 175 watts. It would be a clear lamp with a protected arc tube (M57). My main concern is that it would possibly overheat. There will be a hole on top that would be big enough to accommodate a BT28 lamp and the lamp holder would be above the bucket. I’m wondering if it is something you would do or if I should go back to the drawing board. Many thanks.

I doubt it would overheat. Think about the 175w cram lamps in those old wallpacks!

Yes, I thought about that. I’ll have to give it a try, but I’ll need to get a hole saw first.

I don't think you'll have a problem, it's not going to be fully enclosed, the only thing you'll need to do is make sure that the bucket is grounded, if you're using a metal lamp holder in case of electric shock. 

Yes, ceramic lamp holder and adequate grounding of all parts. Also, I will use high heat spray paint for the exterior.

You'll be fine, if anything the metal bucket should help to dissipate any heat. 

Yes. And the bottom will be open, too so there will be a slight convection updraught.

I should hope so, otherwise the light won't get out... 

Sounds fun!, it’ll be fine, I’ve run a 50 watt merc in a dog bowl before now! 

 I bet the dog wasn't too happy ! 

GOOD NEWS !! I have my setup temporarily hung in the basement and it has been running for about 45 minutes and the temperature of the bucket is only about 35 degrees celsius. The lamp holder is about 100 degrees and is above the bucket. I’m very close to declaring this a success. A picture will follow. There are still some things to complete (mainly cosmetic) and I need to get an enclosure for the ballast and proper wiring.

Looking forward to seeing the pictures. 
There's nothing to beat a good old bodge.!