I have a piece of glass i selected in about 1975, kept the same way up ever since. I'll report back in another 65 years!. Got micrometer readings taken in physics of top and bottom edges.

I think that it will need longer than that. I think centuries are needed to detect this effect.

...which isn't there...

We have man-made glass artefacts dating back around 4000 years. If there was measurable "flow" in 100 years, then all these ancient artefacts would be totally pancaked.

Additionally, you should be able to speed up the flow by subjecting the glass to higher forces. It's easy to do science to some glass and prove that it's elastic rather than malleable at room temperatures.

A centrifuge will do just that.

Confused. What I was trying to state is that the "solid" iron core isn't solid but highly viscous like glass.

Having said that, I'm not sure if glass is actually viscous.I remember being it called an amorphous solid in Physics. As for QI, wasn't the thickening due to the way the glass was fitted? It was never produced perfectly, with one end thicker than the other. When fitted, it was easier to put the thicker edge at the bottom.

Crown glass was spun and was pretty flat. It was expensive though. It was the core was used for glass for the poor, that was thicker at places.