with regards to a lead, the density of the glass doesnt affect the clarity of it, you would need to be fishing a very shallow water, somewhere around a mile off the sun and casting once a minute, so as to keep the lead moving before you could spot mine.
Did tests on my water....gin clear..depths 5-7ft, i dropped one in the margin in six inches of water, and four of us spent twenty minutes looking for it. wouldnt touch anything else now, aside from dung leads for snaggy choddy areas, and only because they take a glug on