2 plain bottles, are they too plain ?

Dear George,
I am very happy that you did post your bottle. It is a super clear evidence of all my previous reasoning about the real wall thickness of Adrian’s bottle. We should be VERY cautious in judging the thickness by transparency. A minimum change of the curvature of the surface can produce an huge variation of the apparent thickness.
Look at George’s bottle, here below.
Without the presence of the snuff, who would not think that the inner wall is in correspondence of the lower yellow arrow and the blue arrow on the right? Everybody will bet that the inner wall is there.
But the snuff is showing, see the red arrows, that the inner wall is in another place, suggesting a thicker wall.
Well, now please do follow the apparent inner wall of the bottom, the one pointed by the lower yellow arrow. Follow that line toward the right corner. If you then follow it upwards, you will see that it goes up in correspondence of the blue arrow. But in the very lower right corner we can see that that line suddenly jumps to the right, going in correspondence of the upper yellow arrow.
So, which is the real position of the inner surface? Is that of the yellow, red, or blue arrows? The answer is that we do not know. Only by eyes, we are not able to safely say which is the real thickness of the wall of that bottle. Each of the three position that we are seeing may perfectly be out of the real position, displaced by the optical effect.
Please remember that that is true even in case of a perfectly plain, transparent medium. The phenomenon is refraction. When the light goes from a medium through another medium of different density, it suffers a change in direction. The fish that we see underwater is not really there, it is a bit displaced. The moon is not there, it too is displaced because of the deviation of light at the vacuum / Earth atmosphere interface.
Imagine when we look something through a rounded surface. We have both refraction and reflection phenomenons in our case, because of the two facing inner and outer walls.
Dear Tom, I believe that it is not right to assume that artificial rock crystal (i. e. glass) is always void of impurities. Why impurities could not be added purposely? That is true for artificial diamonds because of the way of production, but in case of glass it is perfectly possible.
Kind regards
Giovanni