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In the summer purchased a mug from an artist I follow on Instagram. Her work is incredible and I simply couldn't resist!

She fires in a gas kiln and uses white matte glaze inside and out and also sprinkles pigments (I think) on top of the glaze. The effect is absolutely beautiful, the forms are organic, I can go on and on.

But...

After only a few uses I took her mug out of the dishwasher once and made myself another cup of tea (not a coffee drinker here), and my tea tasted like dish water. :( I looked inside and realized that the entire inside surface is crazed/ Probably the outside, too, but I can see the crazing clearly inside probably because the tea stained it. 

As a beginner potter who is only starting to mix my own glazes, I go out of my way to prevent crazing on my functional wares. I don't know if this artist is aware of what happens with the pots she sells and I've been mulling over reaching out and letting her know. I won't ask for my money back (although it would be nice, the mug was expensive and I can't use it anymore :(), but should I tell her that there's a problem and she may not be aware of it? 

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Crazing itself isn't a problem. The issue is if the clay under the glaze isn't fully vitrified and can absorb liquids that seep through the cracks in the glaze. That's likely what's happening here. Is the foot unglazed? If so, after coming out of the dishwasher does the mug leave a moisture ring on the table? That's the telltale sign that the clay isn't properly vitrified.

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I agree with everything said above. Just one question, did the potter specifically say the cup was dishwasher safe? Some potters say ”functional” but expect their pots to be lightly used and hand washed. If the potter did not specifically give care instructions, then the advice should be to label her work as hand wash only.

I have bought my share of “functional” pots that failed for under-vitrification. It’s definitely out there. 

If it were my mug, I would want to be told, given that I do specifically say “dishwasher safe.” 

Edited by GEP
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There is an interesting article from Dr Ryan Coppage, Dr Laura Runyen -Janeky and Ruhan Farsin who did some research into crazing versus non crazing glazes and bacteria.  On Coppage's website there are a number of articles he has written; the one regarding crazing and bacteria is called "Dirty Dishes" and is available to read. His tests were done on porcelain, it would have been good to see a parallel set of tests done on a non vitrified claybody also. 

 

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Thank you all. I will test for vitrification. And will check back the listing description for "handwash only" warning. I guess I still should tell her anyway. I find that every time her posts or stories get into my IG feed now I feel a pang of resentment even though I really like everything about her art, and that fact that she works hard at it, too! 

Thank you for the article, Min. It certainly reassures about the dangers of crazing!

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18 minutes ago, 2Relaxed said:

I find that every time her posts or stories get into my IG feed now I feel a pang of resentment

This is a useful cautionary tale for everyone who is selling, or is thinking of trying it. Customers don’t like it when they feel like they did not get what they paid for.  Make sure to represent your work truthfully. Don’t fudge and don’t assume. Test your work before you sell it!!

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1 hour ago, 2Relaxed said:

It certainly reassures about the dangers of crazing!

It's a good article but I'm not sure how valid the findings are on claybodies that don't have a zero or very low absorption rate. I agree with everyone who has said to let her know if your findings come back showing the claybody is weeping. It could just be that the mug you bought was in a cool spot in the kiln, I was wondering why someone would use a matte liner glaze, underfired maybe? I would want to know if a customer had an issue such as this! I sold a teapot once, had too thick a glaze layer on too thin a base. Customer poured boiling water in it and the bottom of the pot cracked all the way around. I apologized, refunded her money and gave her a free piece. Felt like crap for a while but was super grateful she told me. (and I no longer make potato chip thin pots)

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3 hours ago, Min said:

Customer poured boiling water in it and the bottom of the pot cracked all the way around. I apologized, refunded her money and gave her a free piece.

This has happened to me a few times as well. Customer gets a free replacement, and they can keep the broken one if they want. (Sometimes they still want to use it as a display piece.) On two occasions, the customer was so shocked and grateful at getting a free replacement, they bought another full-price piece. And I, too, learned it’s not necessary or wise to make potato-chip thin pots!

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So, the cup has been sitting on a paper towel for 2 days now, no damp spots under it. Leads me to believe that the clay is fully vitrified. 

So that means that the glaze is a poor match for this clay, is that right? 

PS: like others, I do not understand why use a matte glaze on the inside of functional ware. Although if she used a glossy one that also crazes, it wouldn't help the case either.

 

Edited by 2Relaxed
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Newsprint works better than paper towels, even if the water evaporates from the newsprint it stays wrinkled. This is just a quick but not too accurate test, a more accurate one would be to weigh the pot when it's fresh from the kiln (I know you can't do that now) then put it a saucepan with water and do a low boil for 8 hours then let it cool overnight in the water. Dry all the surface water off then reweigh. The wet weight minus the dry weight divided by the dry weight, with the result multiplied by 100 will give the percentage of absorption of the clay body at that temperature. Under 1.5 - 2% is a good range. Does it still taste like dish water when you drink from it? 

Edited by Min
clarity
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I think that if it was just crazing on a well vitrified body then it wouldn't affect the taste of your tea. I don't see how craze lines could hold enough of anything to affect the taste that much, especially after going through the rinse cycle in the dishwasher. I've sold hundreds of crazed porcelain mugs and never had a single complaint.

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