Author Topic: ABO heat treating  (Read 6558 times)

0 Members and 1 Guest are viewing this topic.

Offline iowabow

  • member
  • Member
  • Posts: 4,718
ABO heat treating
« on: October 19, 2015, 09:04:12 am »
 What are your thoughts; is there a difference in what happens to chert if fired in an electric kiln vs a fire. Now I know these differences do exist but to what end?
As a Potter I am well aware of the effect atmosphere can have on glazes and clay body. So here are a couple thoughts as I ask myself the same question:
1. am I talking about flakes or rocks
2. Color ...so what differences exist?
3. Carbon bonding...dose this happen like in Clay  (i can see some of this in chert)
4. Does carbon bonding improve the quality of the chert or is it the opposite.
5. Other elements and compounds for example those in chert that could oxidize in a kiln but not in a pit. Calcium carbonate might be an example in Burlington.
6. If there are small changes does this make a difference at all.

Observations:
Quartz crystals absorb carbon and create black dots on white Burlington.
White flakes of Burlington seem a little duller than kiln fired flakes.
« Last Edit: October 19, 2015, 09:23:05 am by iowabow »
(:::.) The ABO path is a new frontier to the past!

Offline bowmo

  • Member
  • Posts: 1,035
Re: ABO heat treating
« Reply #1 on: October 19, 2015, 11:10:12 am »
Being another potter I have thought about this a lot. Like the Kaolin I just heated turned red in the roaster but was only skin deep at 550. Would this be different in a outdoor pit...that's a good question. I guess I might find that out soon tho...I burned out my roaster a few days ago trying to ramp up that Kaolin and Mill Creek to 600.  ::)

Offline Zuma

  • Member
  • Posts: 4,324
Re: ABO heat treating
« Reply #2 on: October 19, 2015, 12:43:34 pm »
Don't think I will be much help but I will try to explain
what I think I know. lol >:D
I was trained in electronics where you have to imagine
atomic structure in your mind. It's the electrons that supposedly
create the current when driven by a potential (voltage).
I am not trying to equate heating silica to electronics but trying to
instill the thought of imagining the atomic structures of silica's/feldspars (clay)
and the other materials that get mixed with them. Cherts are not as pure as clear
refined glass. Obsidian is not as pure as glass.
I have come to imagine the crystals not really altering to much with low heat like 500 F because they are created under high pressure and extreme heat. (I think)
 Obsidian is quick cooled molten lava. Cherts/flints/agates/jaspers are usually created  in ancient marine environments via permineralization. Minerals perculating through the earth and getting deposited in limestone cavities.
Long story short-- I imagine the impurities amongst the crystals being reheated to a point where they sort of smooth out and re-glue the crystals together. This is the simple explanation as to why the flakes become more slick and lustrous.
As for abo vs kill I think you will have to use your imagination just because one is controlled  and the other not so much. I recommend the kill because there are charts for time and temp. I use my oven.This keeps the losses minimal. :)
Here is a taste of the Wicki explanation---  :P
Zuma


Silicon dioxide - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Silicon_dioxide

Some explanation in nature---

The only stable form under normal conditions is α-quartz and this is the form in which crystalline silicon dioxide is usually encountered. In nature impurities in crystalline α-quartz can give rise to colors (see list). The high temperature minerals, cristobalite and tridymite, have both a lower density and index of refraction than quartz. Since the composition is identical, the reason for the discrepancies must be in the increased spacing in the high temperature minerals. As is common with many substances, the higher the temperature the farther apart the atoms due to the increased vibration energy.

The transformation from α-quartz to beta-quartz takes place abruptly at 573 C. Since the transformation is accompanied by a significant change in volume it can easily induce fracturing of ceramics or rocks passing through this temperature limit.

The high-pressure minerals, seifertite, stishovite, and coesite, on the other hand, have a higher density and index of refraction when compared to quartz. This is probably due to the intense compression of the atoms that must occur during their formation, resulting in a more condensed structure.

For the Chemist lol Not for me

For example, in the unit cell of α-quartz, the central tetrahedron shares all 4 of its corner O atoms, the 2 face-centered tetrahedra share 2 of their corner O atoms, and the 4 edge-centered tetrahedra share just one of their O atoms with other SiO4tetrahedra. This leaves a net average of 12 out of 24 total vertices for that portion of the 7 SiO4tetrahedra that are considered to be a part of the unit cell for silica (see 3-D Unit Cell).
« Last Edit: October 19, 2015, 01:05:25 pm by Zuma »
If you are a good detective the past is at your feet. The future belongs to Faith.

Offline iowabow

  • member
  • Member
  • Posts: 4,718
Re: ABO heat treating
« Reply #3 on: October 19, 2015, 01:48:59 pm »
Zuma thank you for your input.
(:::.) The ABO path is a new frontier to the past!

Offline Zuma

  • Member
  • Posts: 4,324
Re: ABO heat treating
« Reply #4 on: October 20, 2015, 07:54:31 pm »
De Nada Iowa
I have been blessed with a host of mentors and buddies
that have willing shared all they know to be real.
I try to follow their examples.
I appreciate you as a teacher as well.
Zuma
If you are a good detective the past is at your feet. The future belongs to Faith.

Offline iowabow

  • member
  • Member
  • Posts: 4,718
Re: ABO heat treating
« Reply #5 on: October 24, 2015, 01:36:19 pm »
Here is an example of abo heat treat vs modern kiln heat treating.
The quartz crystals really show carbon uptake. Only one was kiln fired.
(:::.) The ABO path is a new frontier to the past!

Offline caveman2533

  • Member
  • Posts: 640
  • Steve Nissly
Re: ABO heat treating
« Reply #6 on: October 24, 2015, 08:11:25 pm »
I would think atmosphere plays a role in colorization, but I would imagine it is fairly thinly penetrated, Color changes deep with in rock tends to be  more pronounced with longer time soaking at temperature. Largely due I believe to the minerals contained with in the rock.