In our new video lesson, “Tabletops”, we show you how to make a thick glass tabletop. I really like this lesson for its practicality. I live by myself in what some might call a “bachelor pad,” and still more might describe as “underfurnished.”
Most of my furniture came from one store. (I’ll let you guess which one and here’s your hint: everything came with “some assembly required” and a little hex wrench in a plastic pouch).
So this lesson is perfect for people like me because it teaches you how to make something personal that can fit in any size space. In the lesson, we give you the formula for determining the amount of glass needed to make a tabletop of any dimensions you want. And that includes thickness, which I want to elaborate upon.
The thickness you choose for your tabletop will require a few considerations including how much glass to use, and how much time is needed to heat the glass to process temperature.
Most importantly, however, is how much time is needed to bring the glass back to room temperature. The thickness of the glass will significantly affect the amount of time to safely cool the glass to room temperature.
This is because the glass must be heated and cooled uniformly, and for thicker slabs this means there is the potential for large temperature differences throughout the piece, which means greater possibility for thermal shock or other problems.
In the lesson, we create an example tabletop with a thickness of 3/4” (19 mm). A 3/4” tabletop is not an especially thick slab, and so the annealing phase is relatively quick — only three hours — and the prescribed cooling rates through all of the cooling phases make it a relatively quick process. All told, it will take approximately nine hours to safely cool a 3/4” glass tabletop.
But let’s say we jump the thickness up to 1 1/2”, twice the thickness of the example tabletop in the video. One might assume the time to properly cool the piece would also double. But actually, while the time for the anneal soak doubles, the rates for subsequent cooling phases are significantly reduced. (e.g. The cooling rate from 900 degrees Fahrenheit to 800 for a 3/4” tabletop is 45 degrees per hour; the cooling rate from 900 degrees to 800 for a 1 1/2” tabletop is 12 degrees per hour; therefore, with a 3/4″ tabletop it should take you a little more than two hours to go from 900 to 800 degrees while for a 1 1/2″ tabletop it will take over eight hours to cover that same temperature range). In total, a 1 1/2” tabletop will actually need approximately 28 hours to safely cool.
Just for fun, what if you were making a 3” thick tabletop? Again, there would be a significant decrease in the cooling rates. The total amount of time to cool would room temperature would be approximately 99 hours.
And, hypothetically, what if you were making a 6” thick tabletop? The total time would be approximately 375 hours. Yes, it’s a long time.
I’m not telling you this because I think you go and make a 6” thick tabletop. Rather, I am telling you this because I want you to be aware that you have the freedom to make a tabletop as thick as you want — but you must be aware that different cooling rates must be considered for different thicknesses.
Here’s the good news. We have a handy dandy chart that shows you the cooling times and rates for various thicknesses.
Take a look: the Bullseye Chart for Annealing Thick Slabs. Keep it handy when making those tabletops!