From time to time I'll find a crack in some glass item I own where the crack isn't a structural issue, but is only a visual issue. The crack is visible because of the air in the crack causing a sudden change in the refractive index. I'm assuming there are no good ways to truly fix such a crack, but I'd like to make it less visible.
The obvious approach would be to drop on some water or oil that would fill the crack; this should stop the sudden refractive index change and hide the crack. But, this would only be temporary, as the water (and even the oil) would eventually evaporate or migrate away from the crack.
Are there any good, permanent ways to hide a crack in glass?