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There was a bit of a discussion on another thread about crazed glazes on functional pots and whether or not this is an issue if the clay is vitrified. For the most part I make functional everyday pots, vitrified clay, and my glazes don’t craze. I was taught that functional pots shouldn’t craze, significantly weakens them and craze lines can stain.  If the clay isn’t vitrified then crazing causing other issues like moisture getting into the pot, get really hot in the microwave and possible bacterial growth in craze lines. Also, not sure how pleased customers would be if my glazes crazed after use. I’m guessing that for the most part if they didn’t buy a crazed glaze to start with they are not going to want it to craze later on. I could be wrong, I don’t know but I’ve been doing it like this for years and perhaps should rethink this. I think crazing on a coloured transparent / translucent glaze is beautiful.

 

 

So, if you make functional pots with vitrified clay, for your own use or for sale, what do you think? Crazing inside, outside, neither, does it matter? 

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I actually like a crazed celadon for example.

In glaze class in collage I recall that crazing could be a desired effect say compared to shivering which is all bad.

The tension is relived and if the clay is vitrified it can all work.

That said I feel that I should not sell work that has cracked in the functional areas.(insides)Or at least thats my line in the sand.

If the inside glaze has a craze or any cracks its not sold.

The public does not understand any or most of this at all. They only see cracks

I think outside are fine. 

For my own house well thats a different story-I have and use crazed pots.They work in the dishwasher like all other pots. I have not died yet from using them.

D.M.Ernst and Pugaboo like this

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Min:

From my studies; there are degrees of crazing, which I am sure is a relatively new concept in pottery.

 

Crazing 200X

 

This example is not visible to the human eye, unless under strong light and turned so the light reflects across them: but even then hard to see. If you notice, the cracking pattern is almost perfectly aligned and uniform. To me this susgest that the clay and glaze contracted at nearly the same rate. I would not be overly concerned about this type of crazing: not sure it would absorb anything.

 

Check Graing

 

Now this crazing pattern I would be concerned with: you can tell the glaze is weak just by the excessive webbing pattern. I have had pieces of the glaze fall off months later. The closer the pattern, the weaker the glaze is. Notice there are long webbing lines, short articular patterns, and short patterns. All signs this glaze is contracting at a substantially different rate than the clay.

 

COE In clay

 

What most potters do not know is, clay itself can graze in highly vitrified pieces. You can see the solid white body of this highly vitrified body: which most would call a translucent body. Highly translucent bodies are for all intent and reason, are a solid mass of glass.

 

Clay stress under glaze

 
If your vitrified clay does have coe issues: extremely hard to see them because they are under the glaze surface. In this monochrome filtered shot: this piece only had one on the whole body. No big deal.

 

 
When the glaze and clay fit: it looks like this.  This body is also highly vitrified. The body looks as glassy as the glaze.
 

ClayGlaze interface

 

In this cross section, even when no craze line are not visible: there are still small impefections:

 

Clayglaze interface

 
The only crazing I concern myself with is the one above (amber/gold) with multiple craze lines of different sizes and shapes.

 

 
Nerd
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As we ended the thread about whether to sell crazed glazed ware, the only drawback would be a health inspector's rigid standards that reject crazed restaurant ware as being food safe. There are definitely examples of stunning craze glazes like snowflake crazed ware. I guess it is a matter of professional choice. 

 

http://johnbrittpottery.blogspot.com/2010/09/snowflake-crackle.html

 

Marcia

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My feelings about it are pretty much exactly what Mark said.

 

Just one thing to add ... I recently traded mugs with another potter. Her glaze was crazed which I didn't mind. The mug turned out to be a leaker, not vitrified. Sometimes crazing is done intentionally on an otherwise sound pot. Sometimes crazing is an indicator that the potter is short on technical knowledge. Now I will be more careful before buying or trading for a crazed pot, such as asking outright "I love the crazing, but is the pot vitrified enough to use it?" I don't think a knowledgable potter should mind that question. And if the question upsets the potter (because they know their pots leak or if they don't know the answer), then hopefully the potter will eventually realize that addressing this question will be to their benefit.

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Anyone who wood-fires work will have crazed glaze areas on the pieces (inside and out) that are induced by the volatiles in the wood (sodium and potassium compounds) that cause flashing and the fly-ash deposits, even if the glazes used are typically non-crazing.  Nature of the beast. 

 

I use some deliberately crazing glazes......inside and out.  Some of my glazes "fit" (except when wood-fire effects alter them).

 

What I do fits the nature of my work and the client base to whom I sell.

 

Like claywork itself........ there is no "one size fits all".

 

best,

 

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

 

PS:  NOTE:  FYI......... In Japan and Korea you get crazed dinnerware in restaurants all the time.

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 Her glaze was crazed which I didn't mind. The mug turned out to be a leaker, not vitrified. Sometimes crazing is done intentionally on an otherwise sound pot. Sometimes crazing is an indicator that the potter is short on technical knowledge. Now I will be more careful before buying or trading for a crazed pot, such as asking outright "I love the crazing, but is the pot vitrified enough to use it?" I don't think a knowledgable potter should mind that question. And if the question upsets the potter (because they know their pots leak or if they don't know the answer), then hopefully the potter will eventually realize that addressing this question will be to their benefit.

 

In a "different strokes" aspect on this business.... in Japan a number of types of highly prized wares, such as Hagi, are known to typically leak.  It is not considered a 'defect".  It is expected.  Crazed and pinholed glazes combined with a very un-vitrified body.  People there who knowingly buy those pieces for things like yunomi, guinomi, chawan, and sake bottles know that they will have to be treated by traditional methods to "seal" the pores before they can be used.

 

VERY different culture.  :)

 

best,

 

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

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 People there who knowingly buy those pieces for things like yunomi, guinomi, chawan, and sake bottles know that they will have to be treated by traditional methods to "seal" the pores before they can be used.

 

If its not too complicated to explain here, what are the traditional methods to treat this type of ware?

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If its not too complicated to explain here, what are the traditional methods to treat this type of ware?

 

 

The Japanese use a couple of methods.  The first part of the process is to soak the pieces in a bath of water for maybe 4-5 hours.  Then take them out and dry the surface of them off. (Water will still be in the pores.)

 

Then, one approach is to use a heavily boiled seaweed (to mush) liquid that is poured into the piece and left to stand and slowly leak out.  At first it will still leak.  Repeat until sealed. 

 

Another approach is to use the water from boiling rice that is all full of starch.  Same repeat as needed as above. 

 

People in the West sometimes use cornstarch and water in the same way.

 

Then repetitive use with brewed tea or sake helps finish the job. 

 

This is VERY similar to how people in the West used to seal earthenware pottery.

 

With these types of wares it is really important to treat them with respect.  These are not "dishwasher safe" pieces!  By that I mean that they require special treatment and handling.  Because the Japanese understand this and value pottery highly, they take care of them.  They are willing to deal with this kind of issue because....well....because it IS Hagi and it is beautiful and valuable. 

 

You MUST not put Hagi (and other porous wares like that) away wet into a sealed location.  They must get "air dried" between uses.  They need to be stored in a container that keeps dampness at bay (wooden boxes with cloth wrappings fit this bill).   Put them away wet (in the pores) in a sealed place ....and they can mold. (Then you have to bake them and start over.)

 

With my work, I stress not that it IS "dishwasher and microwave safe" but that it is NOT.  This is not "everyday wares".  It is "special" and deserves special treatment and respect.  Like the olden days of "Grandma's fine china" that was brought out for special occasions.

 

best,

 

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

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Thanks everyone! Something to think about. Would make glaze formulas much easier if I don't have to work them out to be craze free (for the outsides). It's interesting that nobody thought crazed pots are structurally less strong yet that gets written about in journal articles etc a fair bit.

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I agree that crazed pots are structurally less strong, but I don't think the difference matters with foodware and household use. Normal daily use will not break a crazed pot. If you drop it on the floor, the uncrazed pot will break too.

JBaymore and Joseph F like this

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Thanks everyone! Something to think about. Would make glaze formulas much easier if I don't have to work them out to be craze free (for the outsides). It's interesting that nobody thought crazed pots are structurally less strong yet that gets written about in journal articles etc a fair bit.

It is actually something I've noticed over time, or when smashing seconds. A mug with a single glaze inside and out (that fits) requires a bit more velocity to smash than one with a different liner/ exterior. Not much, but a bit. And the sound when they break is different.

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One thing I think we forget is that commercially produced tablewares also craze over time when used in the dishwasher. It takes longer but the stress of the heating element breaks down most glazes. What starts out shiny starts to look crackly over the course of a hundred washes.

 

Not to say we should not strive for defect free glaze fit, but we are handmaking items, not manufacturing them. Personally, if a shino glaze crazes that can add to the beauty, but I get that some customers will not see it that way.

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douglas, recently a guest put her plated dinner into the microwave to heat it a little more while i was distracted.  of course, it was one of my favorite commercial plates that has a statement printed on the bottom that it is microwave and dishwasher safe.

 

now i have 3 cracked plates instead of the two that have been at the bottom of the stack for years.  they come out only if there are too many people and i get the awful one.  it has concentric dark lines covering almost the entire plate.  the newest has only a few concentric clean crack lines.

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douglas, recently a guest put her plated dinner into the microwave to heat it a little more while i was distracted.  of course, it was one of my favorite commercial plates that has a statement printed on the bottom that it is microwave and dishwasher safe.

 

now i have 3 cracked plates instead of the two that have been at the bottom of the stack for years.  they come out only if there are too many people and i get the awful one.  it has concentric dark lines covering almost the entire plate.  the newest has only a few concentric clean crack lines.

Ouch sorry to hear that. My general rule with microwaves is never put anything in there if you care about it breaking. But when company is over, you never can predict who is going to grab that piece you really love and do just the wrong thing to it.

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Marcia brought up the subject of the snowflake crackle glazes. How do people feel about those? I have been seeing a lot of functional ware on Instagram lately with really thick crackle glazes. I love one of the snowflake glazes I have been tinkering with and I was thinking about using it as a liner glaze! 😀

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I got your point. Just didn't expect a beautiful pot to go with it. I am currently working using a crackle glaze for the inside of my pots.

 

Just wanted to see other thoughts.

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Figured you did, Joseph.  Just added that in case some folks did not get the reason for the simple picture posting.

 

There will be many folks that will say "poo poo" to crazed functional wares.  Fine.

 

And I agree that if you are storing raw chicken in crazed pots for a while.......... not really a good idea.

 

But given anywhere near reasonable hygiene practices........ not an issue.

 

And yes...... crazing reduces the strength of the ware over what it COULD have been.  Acceptable for me to get the effect.

 

best,

 

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

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Got your point, John but also so happy to see it illustrated on such a fine looking pot.

Does your crackle remain set or does it grow with age?

Wider spaced on outside than in, always?

I have a crackle glaze I use on mugs but just for family and gifts, got sick of the explanation that it was meant and that it is ok

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