heat treating

[iowabow]

Those of us that heat treat please watch this. I think there may be a connection for us. At about 21 mins in he talks about a glass factory accident. Toward the end of this experiment he talks about crystal formation and cooling. I have cooled fast and slow my slow seems better could this be why. https://youtu.be/FYfuI2uZLmg
I knew this from teaching ceramic but did not make this connection untill I watched this. I am going to do a little more research on quartz and silica to see what happens at different temps.
 

[iowabow]

Be careful to watch the whole conversation because he contradicts his statement. I think the second part is correct

[iowabow]

Start at 20 min 51 second

[iowabow]

Some times in ceramics we slow the ramp down during cooling to prevent clouding in the glaze.

[iowabow]

So the question I want answered is are we working with temp that matter or will this matter in some cases but not others. We know novaculite sees high temps and needs very slow ramps ....is this why?
I have questions but no answers

[JoJoDapyro]

With my very limited heat treating, I have found more of an issue with Cooling fast than that of getting it to temp too fast. I lose more stone on the cooling end, than I do the heating end. So what I take from it is that my kiln heats slowly, and cools more quickly. This weekend I'll see what it heats to, I have only ever used one element of the two in it.

[iowabow]

If you don't have digital temp control you could put some additional mass in the kiln.

[JoJoDapyro]

I normally fill it. It is strange that it breaks while cooling. I normally have to wait 48 hours after it is off to be able to handle the stone. I don't ramp down, but the kiln is efficient enough that the cooling time is far longer than the ramp time.

[Chippintuff]

I only have a little experience at melting glass. There are definitely big differences between various glass that is out there, bottles, windows, cookware and even paper weights. The melting points and annealing points of them varies widely. I never had any luck with mixing one batch of glass with another, and I think it was because their reaction to heating and cooling varies widely. All the glass that I worked required temps much higher than 900 F to melt. Maybe he was talking about Celsius. Heating in a hurry never seemed to cause a problem, but cooling fast did. My best results were obtained when I slowly cooled to 800-900 F, then held it there for a couple hours, then continued the slow cooling. The time spent at the annealing temp was critical to their "temper". Some that I held there for longer annealed so hard that I could not knap it.

WA

[JoJoDapyro]

It was Celcius, about 1700 Fahrenheit.
I am strictly talking about stone.

[iowabow]

I normally fill it. It is strange that it breaks while cooling. I normally have to wait 48 hours after it is off to be able to handle the stone. I don't ramp down, but the kiln is efficient enough that the cooling time is far longer than the ramp time.

that is a 10 ramp down but it goes slower at the end. That should be good so I wonder if you are holding at 190

[mullet]

I am now using a small Kiln. I have a high, med, and low setting. The low setting with everything closed up got over 900 dgs before I shut it off and took the thermometer out. I now start out with the lid half on, the two plugs open and a thermometer under the lid. When the Temp starts crawling up I start closing holes and sliding the lid in more till I get the Temp I am looking for. When I think it has been long enough I shut it down and close the lid all of the way and wait about 12 hours before I open it.

 But, I also fill my Kiln to the top.