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Bubbles in Glaze


Narelle

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A 20 min soak will take the glaze over yhe C06 .

The slowing at end has to do with glaze maturation in the case I was stating.

Obviosly in Narele's case yhe schedule used does not work for her glaze.

So one thing at a time.

Alter ramps

Then if not good results, alter soak...20mins seems a long soak at that temperature.

Grind till level with surrounding surface  of glaze. Use a mask. Usually doesnt take much.

If it works use it!

Depends on yhe clay The slow start works for me that's all.

Test and it depends...

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16 hours ago, Min said:

ramp 3   40C / up to 975 / hold until the 06 cone drops, tip  just about touching kiln shelf, probably about 20 minutes plus or minus 10 minutes or so. You would have to test with cones and your actual firing conditions.

Hi Babs,

Yes a 20 minute soak at 999C would take the kiln over cone 06 but that's not really what I was suggesting. I do like doing a soak at the end of a firing, but you are right, it might not be necessary.

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narelle,   you mention a source for your information on how to fire.    could you please tell us what exactly that source is?   the reason i ask is that for the last month or so we have been getting some questions that make me think that some really bad information is out there somewhere.   it appears that some new kiln users think a kiln is like a toaster or some other commonly used heating device.   since many people get all their information on any subject from the internet, i just wonder who is putting this stuff online.

pottery making is part art and part science.   a good textbook would help all these beginners understand that there is a lot more to it than whatever bad information has led them to believe that you turn it on for a number of minutes then turn it up then turn it off.  and that is the extent of their knowledge.  that is so wrong it would be a joke except to the people experiencing the failures.

 

 

BILL,   you might want to re-read your 8:50 am post and check the last sentence for the cone number.

 

 

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13 minutes ago, oldlady said:

narelle,   you mention a source for your information on how to fire.    could you please tell us what exactly that source is?   the reason i ask is that for the last month or so we have been getting some questions that make me think that some really bad information is out there somewhere.   it appears that some new kiln users think a kiln is like a toaster or some other commonly used heating device.   since many people get all their information on any subject from the internet, i just wonder who is putting this stuff online.

pottery making is part art and part science.   a good textbook would help all these beginners understand that there is a lot more to it than whatever bad information has led them to believe that you turn it on for a number of minutes then turn it up then turn it off.  and that is the extent of their knowledge.  that is so wrong it would be a joke except to the people experiencing the failures.

 

 

BILL,   you might want to re-read your 8:50 am post and check the last sentence for the cone number.

 

 

Seven to eight hour cone six is correct. Don’t see the error

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26 minutes ago, oldlady said:

bill, narelle corrected her original post in her second post to 06.   the original was not changed in editing.   

Yes, I see. My point was 400  (200C) degrees per hour is typical so not excessively fast and will result in a 7-8 hour firing even at cone six (6). So cone 06 would end even quicker. There was discussion of eight to ten hour 06 firings which to me seem excessive to get a particular glaze to work. In th end whatever works is the correct method.

 

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On 1/14/2019 at 6:48 PM, Bill Kielb said:

Here is a typical slow glaze program, you might try. This should end in about 7 hours when your 06 witness cone falls.

Rate        (C)                       Temperature     (C)             Approximate time         

65 deg per hour.          To 120 degrees                        1.2 hours                             

200 deg. per hour.      To 900 degrees                         3.9 hours

50 deg.  per hour         To 1032 degrees.                    2.6 hours

 

This is a fairly standard way to enter a ramp schedule in many controllers. Notice, no hold times necessary at this point until we have a real reason to add one. Right now you need a good firing under your belt to see if you have a pinhole issue.

OK, thanks everyone for your help and suggestions, they have helped us a lot.

We used Bills firing schedule above, to refire the mugs with the bubbles, no hold at the end. This got rid of the bubbles and they now look good. 

Yesterday we did another 4 mugs with Fantasy Nebula glaze, using the same schedule. It all was looking good, but the glaze on all 4 mugs has crazed after taking out of the kiln. In fact hours after taking them out of the kiln, you can still hear them pinging.

When the kiln reached cone 06 it was switched off and left cool overnight, the door wasn’t opened until 60c, the mugs were warm, but could be handled without feeling too hot on your hands.

Have done some reading on this, a lot of it saying that a slower heating may be needed.

 

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@Narelle

just a note about crazing. Crazing happens when the glaze shrinks faster than the clay. We call this a glaze fit issue so generally if a glaze crazes on a particular body it is not a close enough fit and will likely always craze on that body unless adjusted chemically to be a closer fit. Crazing can occur right away or hours, days, months later. In general if the glaze does not fit well enough it likely will eventually craze regardless of the firing speed and cooling speed.

a glaze with a marginal fit to the body will also exhibit crazing when the glaze is thicker. Often we see the development in the bottoms of pots where glaze has been artistically applied and intentionally runs down into the center for effect

I have pictures below showing a glaze we are developing for someone at the studio. The glaze was made as a matte and intentionally over melted to get the crystal effect at the bottom of the runs. The bowl is crazed (hard to see in the picture) where thickest, the sample tile is not. 2 grams of  whiting was removed from the recipe to get the fit between body and glaze closer to a match on the sample tile. So far no crazing in the sample tile.

I mention this because I believe  you are using commercial 06 glazes for which there is no published recipe, so this glaze may end up being unsuitable for your claybody regardless of what you do, unless of course you desire the crazed look. Or perhaps it has crazed where applied thick. Generally for mugs, this is not considered a durable finish though.

slower heating likely will not solve this problem.

Finally for our studio we have been doing some basic YouTube videos for those new to clay. Our latest is a basic introduction to glaze, you may find it useful

 

 

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@Narelle

Got to thinking about your glaze as these are specialized lowfire things that don’t have the best reputation for liner use. They tend to craze and some are marked specifically not for food use as I recall. I am not a lowfire clay guy as the body never can be vitrified. Someone might have some and be able to read what is on the bottle. These glazes are designed to mature fully at 04,  A bit hotter than 06. Check your label on the bottle.

 

SAFETY DATA

Ceramic ware that has been coated with Fantasy Glazes should not be used for the storage of food and beverages.

The Fantasy Glazes in all cases are lead free. Several may contain encapsulated cadmium or copper compounds and due to the nature of these types of glazes, they will have a tendency to craze.

Always refer to the bottle for all hazards and safety instructions.

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6 hours ago, oldlady said:

WHY DO YOU SWITCH IT OFF??????????   DO YOU NOT HAVE A KILN SITTER??????   

please post a photo or several to show the controls on the kiln.   a brand name would help.  

No, it does not have a kiln sitter. Built in Australia in 1976.

It originally just had a knob to adjust the temp. Now fitted with a temp controller.

 

DSC_8602.jpg

DSC_8604.jpg

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6 hours ago, liambesaw said:

Some glazes just don't fit your clay body.  Crazing is an indication that there's a poor fit between your clay and your glaze.  Glaze was too tight, don't think firing it slower will help.

Thanks Liam. Bill has also said this is the case.

1 hour ago, Bill Kielb said:

@Narelle

Got to thinking about your glaze as these are specialized lowfire things that don’t have the best reputation for liner use. They tend to craze and some are marked specifically not for food use as I recall. I am not a lowfire clay guy as the body never can be vitrified. Someone might have some and be able to read what is on the bottle. These glazes are designed to mature fully at 04,  A bit hotter than 06. Check your label on the bottle.

 

SAFETY DATA

Ceramic ware that has been coated with Fantasy Glazes should not be used for the storage of food and beverages.

The Fantasy Glazes in all cases are lead free. Several may contain encapsulated cadmium or copper compounds and due to the nature of these types of glazes, they will have a tendency to craze.

Always refer to the bottle for all hazards and safety instructions.

Thanks for your detailed replies Bill. A foodsafe glaze was put on the inside of the mugs, the Fantasy glaze was put on the outside, which wont be in contact with any food or beverages.

I will watch those videos of yours as soon as I have some spare time.

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15 minutes ago, Bill Kielb said:

Nice spot for the controller! I love the handwriting on the original nameplate. 3000 W test kiln, pretty neat stuff. I like old stuff though. Hopefully you have some ventilation in the area or this is outdoors.

Thanks Bill. There was a temp gauge there originally, this was removed, luckily the hole was exactly the right size for the new controller.

Its inside a workshop, but there are big doors on 3 sides, and an industrial sized fan pushes fresh air into the workspace.

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6 hours ago, Bill Kielb said:

..... Or perhaps it has crazed where applied thick. 

Generally for mugs, this is not considered a durable finish though.

 

Bill, the directions said to apply 3 coats, they were brushed on.

Do you mean the crazed glaze is not durable, or the Fantasy glaze in general ?

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I attached the warning they have in their website which says no food storage or beverage storage. In adddition they acknowledge that their glazes often craze which is definitely not good especially for lowfire products that absorb considerable amount of liquids because they don’t fully vitrify.

So most would consider a glaze that crazes not suitable for food service. Personally I would not use this for food service, storage or consumption especially over a low fired absorbant clay body. 

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Many of these lowfire crystalline glazes are decorative only.  Often growing crystals or floating things up in glaze does not yield a low COE glaze so forget about using them on porcelain. It is interesting to go to their website and see the variation they can obtain with less than durable formulas. Starbursts, crystals, flowing movement, and big color at low firing temps, you name it.

The sample I posted is an old Bristol glaze that I was asked to rework for decoration. We will redesign it with a durable flux ratio but the way it works is to make the glaze actually runny (over fired) for the cone being fired and make it be a matte. True mattes are matte because they grow crystals so an over fired runny matte deposits the crystals at the bottom of the run. Titanium (light rutile) is the only colorant so bingo, blue and lavender hues.

not very hard to do actually and I have labeled it as decorative only even after I remove the crazing. It should be a matte but runs so it’s overfired. Why would I ever assume it is durable.

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Also get a timer and place so when half an hourish after expect firing to finish the electricity to kiln shuts off.  In case you get distracted, fall asleep etc.

Is your kiln sitting okn a woiden benchtop?  Better if not the case.

Just saying.

Tetlow used to make great kilns.

Hope your controller isnt getting hot there.

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