Crazing, Pinholes And Food Safety

[Earthwood]

Some of my pieces have tiny pinholes in them, the largest being maybe about 2-4x the size of a period. Most are smaller than this.

Some other pieces have mild-moderate crazing (cracks are generally hairline narrow but vary in number from sparse to plentiful).

 

I am a bit obsessive about food safety. I have heard that you generally do not want to use anything with pinholes or crazing for food because bacteria can grow in the crevices.

 

My question is, how do other potters feel about this? Do any of you sell pieces that could be used for food that have some of these artifacts? (Ex: Some pieces I have bought have had a few tiny pinholes in them). Also, does it make a difference whether the food is dry solids, or wet/liquid?

 

Thanks!

 

- Sam

[Guest JBaymore]

I guess people in Japan should stop using their shino chawans.

 

http://www.artjapan.com/TEBIKI-E/GIF/1/001-02-01.jpg

 

best,

 

....................john

[GEP]

Sam,

 

Since so much of the "info" about this topic is opinion and not fact, you need to develop your own level of comfort and confidence about what you consider food safe.

 

Here are my opinions:

 

There are lots of ways a pots can be unfit for food, but crazing and pinholes are not on my list. My list includes shivering, undervitrification, and leaching of toxic materials.

 

I find it curious that crazing is such a common target of criticism, when to me it seems so superficial compared to undervitrification.

 

-Mea

[Earthwood]

@John - OK that just cracked me up!

 

@Mea - Thank you for your response. You are right, it is an opinion and so it really helps me to hear what others think!

 

Does anyone else have an opinion about pinholes/crazing as concern for food safety??

 

Thanks!

 

- Sam

[hansen]

Yes but - shushi and shino don't go together. The bacteria developing where rare meat or raw fish, or uncooked chicken - yes serious stuff. But from green tea, basil, garlic, etc. different case. It all depends on use. For dinner settings I would try to achieve liner-quality glazes. But for a pot of tea, who even needs a glaze? Tile for counter-tops in the kitchen, sorry these should be as sanitary and continuous a surface as possible if food is going to be worked on them.

h a n s e n

 

 

Some of my pieces have tiny pinholes in them, the largest being maybe about 2-4x the size of a period. Most are smaller than this.

Some other pieces have mild-moderate crazing (cracks are generally hairline narrow but vary in number from sparse to plentiful).

 

I am a bit obsessive about food safety. I have heard that you generally do not want to use anything with pinholes or crazing for food because bacteria can grow in the crevices.

 

My question is, how do other potters feel about this? Do any of you sell pieces that could be used for food that have some of these artifacts? (Ex: Some pieces I have bought have had a few tiny pinholes in them). Also, does it make a difference whether the food is dry solids, or wet/liquid?

 

Thanks!

 

- Sam

 

 

 

[Marcia Selsor]

Hanson is right...bacteria grows in crackle glazes as well as pin holes. Try bisque firing a little higher to assure complete burnout of gases etc. Dampen pots before glazing. Smooth out dried glaze with a dry finger if pin holes developed during glazing. You can try filling the fired pin holes by cramming damp/dry glaze into the hole and refiring.

[GEP]

"bacteria grows in crackle glazes as well as pin holes"

Marcia, I hear people say this all the time, but it doesn't make sense to me. If food or bacteria gets into a crackle or pinhole, it will be removed when you wash the pot. It's only on the surface. I drink coffee out of crackle glazed mugs all the time, and it doesn't make me sick. And in all the debate about the food safety of crackled glazes, I've never seen any proof linking health problems to crackled glazes. To me it is just a myth.

Again to repeat my earlier point, this is just my opinion. And the "bacteria in the crackle" is another opinion. And neither one has a stronghold of proof. And everyone should decide for themselves.

-Mea

[Marcia Selsor]

"bacteria grows in crackle glazes as well as pin holes"

Marcia, I hear people say this all the time, but it doesn't make sense to me. If food or bacteria gets into a crackle or pinhole, it will be removed when you wash the pot. It's only on the surface. I drink coffee out of crackle glazed mugs all the time, and it doesn't make me sick. And in all the debate about the food safety of crackled glazes, I've never seen any proof linking health problems to crackled glazes. To me it is just a myth.

Again to repeat my earlier point, this is just my opinion. And the "bacteria in the crackle" is another opinion. And neither one has a stronghold of proof. And everyone should decide for themselves.

-Mea

 

 

Are the crackles black?If you can see the crackles , is it because they are darker? I don't think washing will remove bacteria. I do follow his leaching and safe glazes advice as he and Ron Roy wrote the mastering ^6 Glazes book. I respect their opinions because they have been professional Ceramic technicians and /or chemical engineers with access to scientific evaluation. I think their concerns for glaze defects and remedies is relevant to all temperatures used for functional ware.

[Marcia Selsor]

Try an experiment.

If you have dark crackles in a functional piece, try soaking it with some diluted bleach with water for 24 hours.

If the crackles disappear, what would that show?

What is the coloration of the crackles?

Marcia

[GEP]

If crackles have been stained with tea or coffee, that's not the same as bacteria or anything that can harm you.

 

Some teapots are designed to not be washed, the flavor of tea gets imbedded into the pot and flavors the subsequent pots of tea, and gets better over time. Doesn't harm people!

 

 

-Mea

[Marcia Selsor]

That is true that tea and coffee stains will probably not harm you. But crazing is a glaze defect. There are many who preach that including Michael Cardew and others.

Some health departments will not let restaurants serve food on crazed dinnerware.

 

From Michael Cardew, Pioneer Pottery pp. 68-69

"A stoneware potter sometimes tends to think that since the body of his ware is vitreous and non-porous, crazing is only a skin-deep and therefore a venial fault; and if he has ever suffered from a body which shatters, he may even be prepared to tolerate crazing as by far the lesser of two evils. But it has been proven that glaze fit has a major effect on strength. Small rods of porcelain, all made by the same process from the same body, are divided into three groups; some are dipped in a crazing glaze, some are left unglazed, others are dipped in a sound glaze; all are given the same firing treatment. The comparative strength after the firing is in the proportions 40:100:160, indicating that vitreous ware with a non-crazing glaze may be three or four times stronger than the ware which is crazed. It will also have a better resistance to thermal shock."

 

If I have a glaze that is crazing and not fitting my clay body, I try to adjust it to get rid of the crazing. This is my practice. I dislike crazing on functional work. We all are entitled to our opinion and professional practice.

[GEP]

No argument with the Cardew reference, but he is talking about structural strength, not food safety. Two different matters.

 

 

 

-Mea

[Marcia Selsor]

No argument with the Cardew reference, but he is talking about structural strength, not food safety. Two different matters.

 

-Mea

 

 

True, but in my opinion crazing is a glaze defect and it is to several others as well. Hammer and Hammer, etc.

repeat

Some health departments will not let restaurants serve food on crazed dinnerware.

 

You have your opinion and I have mine. I agree with you on many of the other glaze defects leaching, etc. It is just the way I was taught and what I have read over the years. We all choose our own comfort zones.

Marcia

[GEP]

Anyone who concludes that crazing is a defect, and decides to avoid it in their own work, has valid reasons.

 

Anyone who wishes to explore crazing as an aesthetic, can do so by making informed decisions about the materials and processes for their ENTIRE pot, not just the glaze, knowing that its possible to make sound, safe, foodware with a crackled surface.

 

I think we can agree on one thing ... that potters will disagree about this until the end of time.

 

 

-Mea

[Marcia Selsor]

Anyone who concludes that crazing is a defect, and decides to avoid it in their own work, has valid reasons.

 

Anyone who wishes to explore crazing as an aesthetic, can do so by making informed decisions about the materials and processes for their ENTIRE pot, not just the glaze, knowing that its possible to make sound, safe, foodware with a crackled surface.

 

I think we can agree on one thing ... that potters will disagree about this until the end of time.

 

 

-Mea

 

 

I completely agree with that. As Chris says...get five potters talking about something and you'll have 15 ways to do something

[Jeri]

Following the topic I found it very interesting the difference of opinions. Now for a question, is it possible to re-fire a piece that has crazing in order to correct the issue? The pot that I have, only has crazing where the glaze is thinner, and no crazing is visible where the glaze 'pooled' and is thicker. I used Laguna's B-mix with Archie's Base by Coyote Clay, which tends to run. I understand that the crazing is caused by the clay and the glaze not being a good fit. I just found it a little odd that the crazing is where the glaze seems to be on the thinner side. I really like this piece, the shape, color, and the overall way it looks and turned out, however, since it is a pitcher, I would like to be able to put it to use.

 

I am like many others where it has been drilled into my head that crazing is not considered food safe, so I have always avoided using something that crazed, and have thrown our mass produced items after they have started to show signs of wear/use from the dishwasher, microwave, etc. So, this topic really does interest me, and I'd love to see the opinion of some others as well.

 

Thanks in advance!

 

Jeri Lynne

[Pres]

Following the topic I found it very interesting the difference of opinions. Now for a question, is it possible to re-fire a piece that has crazing in order to correct the issue? The pot that I have, only has crazing where the glaze is thinner, and no crazing is visible where the glaze 'pooled' and is thicker. I used Laguna's B-mix with Archie's Base by Coyote Clay, which tends to run. I understand that the crazing is caused by the clay and the glaze not being a good fit. I just found it a little odd that the crazing is where the glaze seems to be on the thinner side. I really like this piece, the shape, color, and the overall way it looks and turned out, however, since it is a pitcher, I would like to be able to put it to use.

 

I am like many others where it has been drilled into my head that crazing is not considered food safe, so I have always avoided using something that crazed, and have thrown our mass produced items after they have started to show signs of wear/use from the dishwasher, microwave, etc. So, this topic really does interest me, and I'd love to see the opinion of some others as well.

 

Thanks in advance!

 

Jeri Lynne

 

 

Wow this whole issue makes me feel a little messed up. I used to tell the HS kids that crazing was not an issue with some liquids, but that the tiny surface cracks would absorb a certain amount of sugary, milky, or other juices from the food in them. I also taught them that it was important when building a pot with the intention of serving/eating out of it-that all joins had to be blended out well so that no food particles could be trapped in the form to grow bacteria. I also told them that the crazing would probably not be a problem for years as the small amounts of bacteria would probably not effect them, but I finished by saying for myself I would rather be safe than sorry.

[Mark C.]

What we learned in glaze calc class in the 70's on crazing was-

This was slanted to high fire cone 10-

 

crazing is better than shivering-which is the glaze does not fit the body and jumps off

crazing relives the unequal tension on the glaze as it cools-its not a terrible thing-it shows that it now fits

There are different types of crazing-some can occur under a smooth glaze surface on a slow cool as seen in some celadons

Most times it is felt on the surface

If the body is tight (vitrified) and low absorption (test it) and glaze stays put (stays adhered) cleaning is the main issue

 

Now as to selling interiors with crazing-I would not-I do not view it as prudent as cleaning for me for my customers is what I want to feel great about.

Exteriors are less of an issue for me-

My glazes and bodies tend not to ever craze-you alter the formula to rid it

I saw more of this learning with different bodies and glazes in school-such as many we formulated while learning during glaze calc and the years of experimentation after.

As to me using them myself-I have for many years used a few

The dishwasher cleans them well enough for us-they are really old pots still hanging on.

Mark

 

Pres

Do not sweat those kids pots that crazed-They will be fine-most get broken soon anyway

[Pres]

What we learned in glaze calc class in the 70's on crazing was-

This was slanted to high fire cone 10-

 

crazing is better than shivering-which is the glaze does not fit the body and jumps off

crazing relives the unequal tension on the glaze as it cools-its not a terrible thing-it shows that it now fits

There are different types of crazing-some can occur under a smooth glaze surface on a slow cool as seen in some celadons

Most times it is felt on the surface

If the body is tight (vitrified) and low absorption (test it) and glaze stays put (stays adhered) cleaning is the main issue

 

Now as to selling interiors with crazing-I would not-I do not view it as prudent as cleaning for me for my customers is what I want to feel great about.

Exteriors are less of an issue for me-

My glazes and bodies tend not to ever craze-you alter the formula to rid it

I saw more of this learning with different bodies and glazes in school-such as many we formulated while learning during glaze calc and the years of experimentation after.

As to me using them myself-I have for many years used a few

The dishwasher cleans them well enough for us-they are really old pots still hanging on.

Mark

 

Pres

Do not sweat those kids pots that crazed-They will be fine-most get broken soon anyway

Amazingly enough, I have talked to adults that had me 30 years ago-they still have their pots or their parents do. The are still proud of them, and say that they still show them off. Makes me feel great.

[neilestrick]

As long as my clay body is vitrified, I have no worries about the food safety of crazed or pinholed glazes. But I won't sell pinholed glazes, just from an aesthetic standpoint.