dror Posted May 22, 2017 Report Share Posted May 22, 2017 @glazenerd, Do you think bisque powder or some sand, maybe bisque coasters would help this thermal shock (small stress cracks) you described? Thanks for saving me Link to comment Share on other sites More sharing options...
glazenerd Posted May 22, 2017 Report Share Posted May 22, 2017 Inversion temperature is when the first phase change of silica ( flint) occurs: alpha quartz changes to beta quartz. An extensive vibration of molecules at an accelerated rate, which can crack larger pieces if this phase change occurs too quickly. Matthew v started a thread called " inversion temperature". Do a forum search, you will find the info. The largest flat work I have done is 24" x 24" x 3/4" thick. ( counter top slabs). I work with porcelain almost exclusively. I do however blend in 15percent of molochite to kill plasticity. I used straight alumina hydrate under them, so they would move during the firing. Yes, drag (friction) can also split them. The other possible issue could be how you use your slab roller. You have to make smaller compressions as you, as well as roll in both direction instead of just one. On large pieces, I roll way past the width and length I need, and cut my piece out of the center. The ends and sides are the weakest, so I avoid cutting tiles on the edge of the slab. I have pictures in my gallery, but I am on my wife,s I- pad, and have no idea how to use it to post pictures. Nerd Link to comment Share on other sites More sharing options...
dror Posted May 22, 2017 Report Share Posted May 22, 2017 That's great! i'll look into it! porcelain is a different story but i will definitely try alumina hydrate under them, or bisque sand so they'ed be able to move during firing. your work sounds impressive, i would really like to see it Thanks again for all the tips mate! Link to comment Share on other sites More sharing options...
Marcia Selsor Posted May 22, 2017 Report Share Posted May 22, 2017 when I was in Grad school, we had a global-bar kiln. They are bars of silicon carbide that heat the kiln. One student loaded the kiln solid with tiles. The glo-bars were destroyed. End of story. Marcia Link to comment Share on other sites More sharing options...
Benzine Posted May 22, 2017 Report Share Posted May 22, 2017 The other possible issue could be how you use your slab roller. You have to make smaller compressions as you, as well as roll in both direction instead of just one. On large pieces, I roll way past the width and length I need, and cut my piece out of the center. The ends and sides are the weakest, so I avoid cutting tiles on the edge of the slab. Nerd Good point. There have been numerous discussions here about rolling out slabs, especially those that are large. Many, who work a lot with slabs will flip and rotate their clay slabs in between rolling. In other words, they partially thin it with the roller, then rotate it 90 degrees, as well as turn the entire slab over. This is done with each successive pass. That way slab is receiving the same amount of pressure all around. I don't work with large slabs, so I cannot say how well this prevents cracking/ breaking. Just to be safe, I even do it with my smaller slabs, everything from several inches by several inches to slabs that are even smaller. Link to comment Share on other sites More sharing options...
glazenerd Posted May 23, 2017 Report Share Posted May 23, 2017 Dror: This is the largest tile I make. It starts out as a 14 x 20 and ends as a 12 x 16 after I trim it. Fred Sweet has offered me his life savings for it, but I refused to sell it to him because I recall him distinctly telling me at NCECA 2016 about his issues with "blue." But that is another story, and I will let Fred tell it..... I did tell him however if he ever shaved his beard and made me some glaze brushes from it: I would swap him straight up. Nerd Link to comment Share on other sites More sharing options...
Fred Sweet Posted May 24, 2017 Report Share Posted May 24, 2017 Aaah, Nerd. Now you went and told the whole CAD world about my secret. Not only that, but you've probably started a bidding war that I'm not sure I can win anymore. Good to hear your teasing, and a great looking tile to boot! Link to comment Share on other sites More sharing options...
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