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I don't know what to call this type of formula/chart.
Is there a formula or a chart for holding time + temperature = the same result in glass as a different holding time+ different temp?
For example; if I go to 1150F and hold for 60 minutes that produces the same results as 1200F at X minutes hold?
Mary

Unfortunately, there isn't one. It's the Holy Grail for fusers.

Brock, I've been searching your posts. Long ago you posted a slumping schedule that included 1150F at 60 minutes hold. I copied that down back then, I tried it yesterday, but it didn't quite do it for my small molds. I didn't watch my slump and my finished result has not slumped all the way. So I thought I would give it another go. I liked your idea of going so low and a longer hold. I just thought I would add more time, but unsure how much, then thought "what would happen at a little higher temp"?
You know how it works; one thought leads to another so I thought of the "Holy Grail" question. I thought I had seen such a formula/chart somewhere. What would you call such a formula/chart if it did exist?
Mary

Maryar wrote:What would you call such a formula/chart if it did exist?

Impossible. Or incorrect. Or misguided.

Take your pick. You can't come up with the perfect chart for the same reason you can't come up with the perfect firing schedule. Kilns are different, glasses are different, slumping molds are different, kiln shelves are different. All of those factors (and more!) mean that any attempt to come up with the kind of chart you're looking for would have to be very specific -- i.e, for this kiln, with this glass, with this shelf, with this rate of temperature increase, etc. etc.

It truly is a Holy Grail. And, like the original one, one that probably can't be found.

. . . I just thought I would add more time, but unsure how much, then thought "what would happen at a little higher temp"? . .
What Brad said. I am a huge proponent of LOOKING in the kiln to control processes.
As a general rule, a smaller mold, or span, may require a longer hold or a higher temperature.

I totally agree, different results for everyone. Even the same brand of kiln with same brand of controller can be different. There is no absolute perfection in glass working. It is an art.
But as there charts put out by different manufacturers to go by; Bullseye, Spectrum, Uroboros, all have their suggested schedules. I was hoping that someone in the glass industry, with all their scientific equipment to help them, may have figured out that if you do something at one temp and hold, that you can achieve near the same results at a suggested higher temp and suggested shorter hold.
I guessed that Brock probably was working on larger items than myself.
I'll watch.
Thank you.
Mary

In the same kiln, with the exact same load, same weight and colors of glass, mold and mold placement, you should be able to fire consistently with the same heatwork using the same schedule (until the thermocouple degrades).

The science for what we do has so many variables, that exact answers are not available. This is true for both heatwork and annealing. Both require seat of the pants engineering based on observation and experience. When it comes to heatwork, there is no substitute for looking. Be aware that heatwork in one kiln can be extremely different from another kiln, using the same program.

As Bert said, each kiln, mold and glass is different. If you use the same set up you could run a series at different temps to an observed "full slump." You can than generate a graph (curve) for each. The area under the curve is heat work. You can than use calculus to measure the area under the curve. It's called an integration. Don't ask me the formula as I have not used calculus in 50 years. All curves with the same area under the curve should have equivalent heat work. You could than draw curves with the same heat work but at different temperatures and/or times and project from each what would work (equal heat work.) Find a good high school or college math professor to help you.

Warren

Warren writes what is pretty close how I think. You can make a controlled series of experiments and produce a curve of heat work.
With better equipment and more scientific rigor you may end up with a formula temperature vs viscosity. That may get a bit closer.

There remains one open question *how the heat works*! I have made some deep bowls with striped patterns. During the slump the stripes widen differently. At the same firing clear glass flows more than opals. To work this example further: at extremely high and fast schedule the opals absorb heat faster than transparents, dark colors faster than pale. They are not in the same temperature. With a slow and low schedule these differencies are smaller. Read it right; different time/temperature combos do not give exactly the same result.

We are back in the square one. Experiment, peek and keep good notes. Tha graal is elusive, maybe it do not exist.