The idea is that as the glass comes down the ribbon it is scored and broken to size. Then it is cleaned and put through the tempering oven. If not cleaned well, the glass fines from the scouring and breaking of the glass would remain on top. Then both the fines and the sheet would soften at the same time. And having the same coefficient of expansion they would melt together. Hence fusing together. Such a thing should be EZ. So the experiment was performed. At the precise standard temperature that is used in a tempering oven. The glass fines, and silicates/sand particles could not be made to fuse with the surface. To learn more about this I looked into the hot art glass industry. They fuse glass to glass all the time. Even fusing window glass to window glass. Float to float! You can watch videos of this being done on the Youtube, So whats up with this? Well check out this info taken from the Wikipedia;…
Fused glass is glass that has been fired (heat-processed) in a kiln at a range of high temperatures from 593 °C (1,099 °F) to 816 °C (1,501 °F). There are 3 main distinctions for temperature application and the resulting effect on the glass. Firing in the lower ranges of these temperatures 593–677 °C (1,099–1,251 °F) is called “slumping”. Firing in the middle ranges of these temperatures 677–732 °C (1,251–1,350 °F) is considered “tack fusing”. Firing the glass at the higher part of this range 732–816 °C (1,350–1,501 °F) is commonly described as a “full fuse”.
So what is the standard temperature in a tempering oven? It is 620 C. That is just below the middle part of the temperature range used for slumping. Not even tack fusing. Never mind a full fuse! When glass is raised to its slumping temperature it just becomes soft and will slump under it’s own weight. So it stands to reason that any glass fines or sand particles would be easy enough to press into the surface but they would just pop out. Which is what happened.
I personally believe there are many reasons for scratching. As I have proven to myself that just rough glass by itself sensitizes glass so that many things that otherwise might not scratch glass now will. Including fabrication debris. I can easily sensitize a window with cerium or HF or sulfuric and scratch it with loose glass fines/fabrication debris. Definitely sand particles will scratch sensitive rough glass surfaces. So is there something else going on in the float glass bath that is chemically changing the surface to make it rough? In particular the tin side since that is the side that typically exhibits a roughness? We will have to wait on that. But it is a question that shouldn’t be ignored. As for the “tinkling sound” that we all for many years have believed to be “fused” fabrication debris/glass fines, this appears to still be up for analysis. It is still being studied to the best of my knowledge. In my research into the chemistry of the tin side and the air side of float glass I have learned that there are many different chemical reactions that happen. This is one reason why the atmospheric conditions and the chemistry of the molten tin must be very precisely controlled. That liquid tin by the way is not changed very frequently. The line goes on for many months. Even more than a year. 24/7 none stop! Because there is tons of money involved. There is much to be learned. So much more than we could possibly know in advance of the research.
I will answer your two questions VERY plainly however.
Fused Fabrication Debris is not a myth, it is a misunderstanding.
Also scratches are caused by many different conditions on both new and old glass.
Based on your theory of something ekse in the process having an effect do you think it’s possible that the issue with scratched glass is because the tin side is exposed and there was an unissual effect in the process along with maybe other contributing factors like fabricating debris being present?
Interesting idea. I think we know that there is definitely something afoot with the tin side. Also glass is washed to remove any left over glass fines and possible sand particles. So these could be a part of the mix. Just that they do not fuse at the standard temperature of a commercial tempering oven. Good question. In my opinion. I am waiting for the next level of testing to come out. Anxiously!
