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Underfiring and pinging


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#1 jgmaturpen

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Posted 09 April 2012 - 08:00 AM

I am making tile for a kitchen showroom. The clay is 5 bmix with grog using laguna's robins egg blue glaze. I ran a test fire last week with at a standard speed ramp to cone 5 but my kiln failed to heat and shut down at 2075. The good news was that the tests were fine and the robins egg looked great. So, I glazed all the tile and set the kiln on a slow ramp to cone 3 thinking that that would get me close to 2075. The controller showed that it reached 2034 before it started cooling. I opened the kiln this morning everything was warm but I could hold them with no problem. Then the pinging started. The tiles are pinging but I am not seeing any signs of crazing. I did notice that two of the tiles that I pulled have hairline cracks on the back in the exact same location. The other problem was that the glaze did not come out the same. It has less spot development and the color is greener than blue, they would work, they are just not quite as beautiful color. My question is, should I restart the kiln and try for a higher tempature or is that too risky as far as the cracking goes? Or should I just do the best with what I have? And, of course I am under a time deadline. Thanks

#2 Mark C.

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Posted 09 April 2012 - 10:29 AM

The tiles need to be vitrified to be strong-that is fired to cone 5. They are not there yet
Not sure about the 2075 why or whatever-but the tiles need to be fired to cone 5 . You can refire them but the glazes will look different than new ones fired to cone 5-all refires look different than the first time around.
If the glaze is talking and tiles are cracking my guess its its a matt glaze pulling the tiles in 1/2 and you will have some loss
If you want them all to look alike than paint is better than glaze as glaze always has some degree of change in it-its the nature of ceramics-
I suggest a new load fired to cone 5-are you spraying the glaze as this works best/easiest for tiles?
are the tiles scored on the backs as this also gives then strength with matt glaze on front?
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#3 Chris Campbell

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Posted 09 April 2012 - 10:30 AM

This stuff always happens when you are under a deadline ... always!
Pinging means the clay and glaze don't fit. One is shrinking faster or slower than the other and somethings gotta give. Just because you cannot see it with your naked eye doesn't mean its not happening ... the ping says it all.
I don't think firing higher will solve a glaze fit problem but I could be wrong. If it is the color you want to be better, than refiring could help.
Are these tiles going to need to be waterproof or are they just for looks? If they are already pinging and cracking I would not use them in a water sensitive situation.

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#4 jgmaturpen

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Posted 09 April 2012 - 10:43 AM

They are just for looks.

The hairline cracks are only on the back of the tile and in the same area on each of the tiles.

The pinging is continuing well after being out of the kiln and at room temp, although I am scared to remove the rest of the tile until the kiln is completely cooled to room temp.

The glaze is not matte. One thing that was different when applying the glaze, was that the glaze looked like a desert as it dried. It still adhered but if I touched them it popped off. I was trying to reach 2075 because that is the tempature the test tiles reached and since these aren't functional tiles I wasn't worried about them not being fully vitrified. Was more concerned about matching the test results.

#5 bciskepottery

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Posted 09 April 2012 - 06:50 PM

The pinging could be the result of removing tiles from the kiln before they had properly cooled. I generally do not remove glaze ware from the kiln until it is under 100F. Even at the lower temperatures of cooling, the glaze is still interacting with the clay body.

If the clay body and glaze are both rated for Cone 5, then firing them to less than that could result in poor glaze fit (e.g., crazing). You may not see it right away, but it will eventually show up.

I'd be concerned about hairline cracks. That is a weak point and, over time, the tile will continue to crack -- and who wants to have to replace cracked tiles that have been set into a wall? You can score the back sides, fire the tiles on cookies or flat bars to reduce stress during firing, etc.

#6 Mark C.

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Posted 09 April 2012 - 07:13 PM

I am making tile for a kitchen showroom. The clay is 5 bmix with grog using laguna's robins egg blue glaze. I ran a test fire last week with at a standard speed ramp to cone 5 but my kiln failed to heat and shut down at 2075. The good news was that the tests were fine and the robins egg looked great. So, I glazed all the tile and set the kiln on a slow ramp to cone 3 thinking that that would get me close to 2075. The controller showed that it reached 2034 before it started cooling. I opened the kiln this morning everything was warm but I could hold them with no problem. Then the pinging started. The tiles are pinging but I am not seeing any signs of crazing. I did notice that two of the tiles that I pulled have hairline cracks on the back in the exact same location. The other problem was that the glaze did not come out the same. It has less spot development and the color is greener than blue, they would work, they are just not quite as beautiful color. My question is, should I restart the kiln and try for a higher tempature or is that too risky as far as the cracking goes? Or should I just do the best with what I have? And, of course I am under a time deadline. Thanks



I looked up your glaze color in my Laguna catalog-My suggestion is go to a tile store and buy them as that is a very common color on commercial tile-that way the deadline is met and the tile will be durable and will all look alike as you seem to want this aspect .

If you do not like this suggestion my 2nd choice would be make all the tile again and spray the glaze evenly and fire to cone 5 and hope you get good results.
I have made enough tile to know the 1st option is the easiest by far.
Mark
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#7 Lucille Oka

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Posted 09 April 2012 - 11:32 PM

I looked up your glaze color in my Laguna catalog-My suggestion is go to a tile store and buy them as that is a very common color on commercial tile-that way the deadline is met and the tile will be durable and will all look alike as you seem to want this aspect .

Mark


Mark, this is a disturbing suggestion to me. If the customers are expecting handcrafted tile that is what they should be given doing otherwise even in a pinch smacks of a lack of integrity.

If you must get commercial tiles you can find unglazed bisqued tiles and glaze them but please pay attention to the maturation point of the clay used for the tiles and get a suitable glaze in a similar color to the one you promised your customer. The bisqued tiles are already keyed and can be found at ceramic suppliers. You cannot call them handcrafted but you can call them hand decorated.

John 3:16
"For God so loved the world that He gave His only begotten Son, that whosoever believeth in Him should not perish but have everlasting life".

#8 Mark C.

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Posted 10 April 2012 - 12:02 AM


I looked up your glaze color in my Laguna catalog-My suggestion is go to a tile store and buy them as that is a very common color on commercial tile-that way the deadline is met and the tile will be durable and will all look alike as you seem to want this aspect .

Mark


Mark, this is a disturbing suggestion to me. If the customers are expecting handcrafted tile that is what they should be given doing otherwise even in a pinch smacks of a lack of integrity.

If you must get commercial tiles you can find unglazed bisqued tiles and glaze them but please pay attention to the maturation point of the clay used for the tiles and get a suitable glaze in a similar color to the one you promised your customer. The bisqued tiles are already keyed and can be found at ceramic suppliers.


Lucille
I was only trying to help with the deadline part as the technical issues are going to take time to work out- And a deadline was mentioned so I focused more on that.I thought about the handcrafted idea and posted an alternative way to work the issue out within a deadline.It was also noted that they do not look alike and the commercial tile would also cure this as well.This issues all take time and it was mentioned that a deadline was in place.
I also thought about the bisque tiles and assumed that would be a known option-I took the time to look up the color choice and suggested a quick cure focusing on the deadline. My second suggestion is do it again and noted that really is a ton of work . I am all about integrity and stand behind this post. Nowhere in the postings was there mention of expecting hand made tile from customers.
Sorry you took this as disturbing I never meant it that way. I am all about sharing how to info if I know the subject. Please take the time to review any of my others posts and you will see a helpful sharing of ideas.
Mark
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#9 Lucille Oka

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Posted 10 April 2012 - 01:13 AM

Lucille
I was only trying to help with the deadline part as the technical issues are going to take time to work out- And a deadline was mentioned so I focused more on that.I thought about the handcrafted idea and posted an alternative way to work the issue out within a deadline.It was also noted that they do not look alike and the commercial tile would also cure this as well.This issues all take time and it was mentioned that a deadline was in place.
I also thought about the bisque tiles and assumed that would be a known option-I took the time to look up the color choice and suggested a quick cure focusing on the deadline. My second suggestion is do it again and noted that really is a ton of work . I am all about integrity and stand behind this post. Nowhere in the postings was there mention of expecting hand made tile from customers.
Sorry you took this as disturbing I never meant it that way. I am all about sharing how to info if I know the subject. Please take the time to review any of my others posts and you will see a helpful sharing of ideas.
Mark




Mark, I have been amazed by your posts and how much you do share and you should be commended. I have read many of your posts. I have never thanked you for them, even though; many times I wanted to do so, for you are very generous with your knowledge.

I realize you were seeking a resolution but this is the first time one of your suggestions 'cut me to the quick'. I don’t know what else to say.


John 3:16
"For God so loved the world that He gave His only begotten Son, that whosoever believeth in Him should not perish but have everlasting life".




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