Fact or Fiction?

Can you see glass flow in the windows of old buildings?

Is glass flow real or myth?  Look at this picture and decide for yourself.

As you can see, the different window panes are uneven.
This is an example of glass flow. 

What is glass flow?

Glass flow is the thickness and waves your eyes see in old window panes. 

These waves give the appearance that the glass is “flowing.” Some people, however, say there is no such thing.

The myth stems from old scientists who looked at the stained glass windows in cathedrals and noticed that the glass was thicker at the bottom than it was at the top. This myth exists because some scientists believe the glass was pulled by gravity at room temperature. People assumed that over time glass “flowed down” which created that thickness.  In reality, the thickness is a result of how the glass was made.  Medieval glass was made by blowing a giant glass bubble on the end of a blowpipe.  This bubble was cut open at the end and spun into a huge disk.  When the disk cooled, it was cut off and diced into windowpanes.  The panes were of different thicknesses because of the stretching that happened while spinning the bubble into a disk.

Molecular Makeup

Liquids flow because there are no strong forces holding their molecules together.  Their molecules can move freely past one another, so that liquids can be poured, splashed around, and spilled. But, unlike the molecules in conventional liquids, the molecules in glasses are all held together tightly by strong chemical bonds. It is as if the glass were one giant molecule. Modern studies of glass shows that glass stops behaving like a viscous liquid and becomes a solid once it cools to a certain temperature.  Its capacity of heat and other characteristics are consistent with its being a solid as well.  Therefore, glass has a transition temperature, the temperature where it changes from a liquid to a solid.  That temperature is well above room temperature but that exact number is not known.  

 What People Think

The majority of the people surveyed answered that they were unsure of you can see glass flow in the windows of old buildings. The minority of the people answered that being able to see glass flow in old windows is fiction. The number of people who answered Fact is in the dead middle of the majority and the minority. 18 people were asked this question and the average age of these people is 14.3 years old.

The majority of the boys answers are that being able to see glass flow in the windows of old buildings is a fact. However, the boy’s answers are pretty evenly spread out. Most of the girls who answered the question had the same opinion. Their answer to the question was unsure. Very few girls answered fact or fiction. The average age for the boys is 14.4 years old. The average age for the girls is 14.1 years old. Nine boys and nine girls were surveyed.

Conclusion

The myth is fiction. You can not see glass flow in windows of old buildings because it takes billions of years for gravitational forces to move glass at room temperature.