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.
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!
After a cave dive, my Subal 8" dome port had several scratches, right in the middle! THey are not deep, but the longest one is 2 cm long.
I've read all the posts in this thread, but from the 7 pages, only those two addresses the problem of glass domes (maybe ir will be appropriate to create two different topics - acrylic and glass - to be easier for future reference...?
Anyway, I live in Portugal, so maybe some can post advice regarding where can I buy that glass polishing kit, inside EU?
Also, has anyone more tried to polish glass domes?