Hi all,
I have a Subal glass dome with a scratch in it that definitely affects the images more that I can ignore so looking to see if there is any agreed upon DIY approach.
To be exact it is not as much a scratch as it is an abrasion of what I suspect is the coating. The result is a triangularly shaped rough and matte patch around 5 mm wide. When shooting just a bit against the light, the reflection of the patch shows up in the image as a blurry patch in the image. I can not afford a replacement dome but am willing to try to fix it myself. Or perhaps take it to an optician or someone else. If anyone has good advice let's try to compile it here.
I read through the amazingly helpful thread on what to do with scratches in acrilyc domes. I found two posts that dealt with glass domes and have taken the liberty to copy-paste them here. I was wondering if the original posters (or others) can tell me more about their final results - I am particularly worried about losing coating once I start this process, though losing the roughed up coating due to the abrasion is probably needed and better than what I have now, I am wondering whether the transition to the unharmed areas of the dome will be smooth and whether the uncoated, but at least polished patch, will show up in images afterwards?
From Yellowmon on June 20, 2009:
Glass port scratches are as problematic as they are inevitable. Fortunately, it is possible to remove scratches in glass ports if the scratches are not too deep. Stephen Frink suggested to me I use "jewellers rouge" which I found on Amazon. I used a Dremel which has a power cord (when I tried with battery packs, ran out of juice before finishing) and a whole bunch of felt polishing wheels (catalog #414). It took a long, long, long time. Perhaps an hour but the minor scratches did disappear. I went through a number of felt wheels. It is a long and boring process but gives one time to reflect on the dangers of rocks attacking poor defenseless dome ports and to be more protective in the future. I write this now as I am preparing to attend to another session of polishing, which I hate as much, if not more, than cleaning the camera's sensor (also necessary this weekend). While you are out diving and having fun, think of a tiny wheel spinning round and round and be thankful if you have acrylic domes how much easier they are to repair.
I can't guarantee this process will work for everybody but so far it has done well for minor, hairline scratches and little dings. I hope this advice cuts into the sale of replacement Seacam domes, Harald is doing far too well these days.
Good luck!
From Kogia, August 18, 2009:
I had been told by opticians and housing manufacturers that it is not possible to polish out scratches from glass domes: they must be replaced. However, after reading this post, I did some searching online, and found a DIY Glass Polishing Kit for $40 at www.hobbytool.com. I had a couple of scratches on my glass dome that were not deep, but close to 2cm long, and managed to produce really ugly black scars on the image files when shooting into the sun. To my utter astonishment, they disappeared after only about 20 minutes of polishing using an electric drill with the wheel, pad, and polish solution provided in the kit. Best $40 I ever spent. Thank you Yellowmon!
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Here are some images of the worst of the abrasions/scratches on my dome(reflection is of same patch on underside of glass dome):
) after repairing it. The scratch in mine is more of a straight-line gash, rather than the rash-type scratch you've got. I hope it works (for BOTH of us)! 
