I've been a fan of acrylic domes for underwater housings over glass domes for years. I recently was convinced to try glass domes again -- and I discovered that manufacturers STILL have not solved the problem of these glass domes etching or staining!
Many underwater housing manufacturers are moving towards using glass ports for housings now. I first encountered this problem with a Subal dome 20 years ago. According to Subal, if one did not scrupulously wipe off the water off a glass port, it would stain over time. Sure enough, that glass dome stained. No one that I know, in all the world of underwater experts, knows how to remove the stain once it hits a glass dome. I would never
have bought a glass dome if I had known that this sort of thing was
still a problem.
So underwater shooters -- be careful. If you have a glass dome, be sure to dry it off with a microfiber cloth after every dive. Never leave a wet neoprene cover on a glass dome.
I've just been jumping in and out of the water off Isla Mujeres, several times a day, so trying to wipe down my dome port and keep it dry and maintained to prevent further staining has been a real pain in the butt. I am going back to acrylic domes.
I've always preferred acrylic domes because I can fix any
scratches myself. In Bali a few years ago, I forgot my dome polishing
kit, and I just used sand from various beaches and ended with toothpaste!
One source tells me that glass is preferable to acrylic because it flares less when shooting into the sun. I hope to test this sometime.
Berkley White, prolific shooter and owner of Backscatter, wrote me:
To prevent etching, you must never leave a wet dome cover on the dome and blot off the dome after rinsing. Even then I use a little Novus2 every few days to minimize mineral build-up.