Dishwasher and microwave safe pottery

[LotsToLearn]

How can I make food safe pottery that is microwave and dishwasher safe? What are the clay, glazing and firing requirements? 

[Babs]

Search these forums ,there has been a lot written up on these issues

[Bill Kielb]

To me clay with low absorption, fired to full vitrification and a matching durable food safe glaze. For food ware I like clay bodies less than 1%, usually 1/2% if practical. Laguna frost porcelain has been a late favorite. I also like a well fitted food safe glaze, no crazing etc… I usually glaze the bottoms of many things as well just to make them finished, durable with less surface to absorb water.

Edited May 7, 2022 by Bill Kielb

[neilestrick]

Vitrified clay body with an absorption rate below 1.5%, typically fired to cone 5/6 or above. If you're using commercial glazes, they'll be labeled for food safety, but you'll need to test them for durability.

[Pres]

Over the years, I have moved from a semi matt zinc based glaze to a glossy liner glaze, with a series of overglazes sprayed. Even then I have lowered the amount of unglazed area until now it is just a small foot ring on the piece. I have also moved from looser firing clays to clays that have a much less absorption rate. The years tell the story, as the old zinc base semi matt mugs and pots are showing all sorts of signs of wear. The glossier glaze base glaze which is a transparent liner glaze with added opacifiers is extremely strong and impervious to dishwasher and other abuses.

Age and experience has a lot to do with the journey, and the lack of stubbornness to continue down the same road for fear of change.

 

best,

Pres 

[Piedmont Pottery]

When I make a new glaze, after testing for food safety  I test for dishwasher safety.  I glaze fire a test strip with the glaze under the normal firing conditions I use, and then submerge the test strip halfway in a very concentrated automatic dishwasher detergent solution and then leave it there for 4-5 days.  I look for any changes in color, reflectivity, glossiness, and texture between the half that was submerged compared to the other half.  I also look for any color transfer to the detergent solution.   If it withstands these extreme exposure conditions, I feel confident that it will not be damaged in a normal dishwasher cycle.

[Min]

1 hour ago, Piedmont Pottery said:

and then submerge the test strip halfway in a very concentrated automatic dishwasher detergent solution and then leave it there for 4-5 days. 

How to quantify and standardize the bath solution though? It's my understanding that the often recommended simmering of samples in a 5% soda ash solution is an adaption of the ASTM C614-20 where tetrasodium pyrophosphate is used to test porcelain enamels that line some sinks, dishwashers and washing machines. I have done the 5% soda ash test many times but found that it is harsher than a real world test of leaving a sample in the dishwasher for several months and actual daily use of pots going into the dishwasher over the years.

I would like to see a some definitive data on this but have yet to find any. Have you done the 5% soda ash test and compared those results with your method? Would be interesting to compare the two methods and then quantify your method and use that instead of the months in the dishwasher test or soda ash method.

[Roberta12]

I attended a workshop last weekend . The presenter said the dishwasher is hard on glazes because of the alkaline nature of the dishwasher soap and the constant hot water. He also mentioned the absorption as Neil said.    I have always put my work in the dishwasher.  Endless times.  There is however, one glaze that I use, that I think might be seeing the effects of dishwasher abuse over time.  I have not decided what I am going to tell customers.   The glazed pieces in question are years old.  Years.  And it's only one glaze, that I have seen visible effects on.  

[Bill Kielb]

2 hours ago, Roberta12 said:

The glazed pieces in question are years old.  Years.  And it's only one glaze, that I have seen visible effects on.  

The dishwasher is harsh on all. Alkalinity, the insidious repeated process of removing a brick from the structure and replacing it with a smaller brick so to speak weakens and wears away ALL wares over time. Even those bought from the store. All accelerated by the dynamic action of the velocity of the water. Hey, water in motion, seems I remember something about it carving out the Grand Canyon. I like to believe it’s reasonable to try your best to make durable wares and glazes ……… it seems to be a seasoned and reasoned approach for experienced potters IMO.

[Mark C.]

My pots go into the dishwasher almost daily with no effects-The dinnerware is made in the 70's. The cone 10 work holds up really well either in stoneware or Porcelain . If I was firing cone to cone 6, I would test the heck out of as all have noted.

[neilestrick]

6 hours ago, Mark C. said:

My pots go into the dishwasher almost daily with no effects-The dinnerware is made in the 70's. The cone 10 work holds up really well either in stoneware or Porcelain . If I was firing cone to cone 6, I would test the heck out of as all have noted.

I don't think cone 10 work is inherently more durable than cone 6 work. I've got pots from both cone 6 and cone 10 firings that have etched from the dishwasher, and pots from both that are just fine. I've also got some cone 3 pots that are durable. A good glaze is a good glaze, regardless of the firing temp. Durable commercial dinnerware is made at a wide range of temps.

[Bill Kielb]

25 minutes ago, neilestrick said:

A good glaze is a good glaze, regardless of the firing temp

To back this up there are tested cone 04 / 6 boron glass recipes that have tested more resistant to erosion in the dishwasher  than their cone 10 counter parts.

[Mark C.]

15 hours ago, neilestrick said:

I don't think cone 10 work is inherently more durable than cone 6 work. I've got pots from both cone 6 and cone 10 firings that have etched from the dishwasher, and pots from both that are just fine. I've also got some cone 3 pots that are durable. A good glaze is a good glaze, regardless of the firing temp. Durable commercial dinnerware is made at a wide range of temps.

That's most likely the case-just saying its NEVER been an issue for my wares/glazes/clays at my temp range the past 50 years

[Bill Kielb]

On 6/5/2022 at 1:12 PM, Mark C. said:

its NEVER been an issue for my wares/glazes/clays

A lot of the wear is fairly microscopic. True some awful glazes bleach out easily or degrade quickly but I would think unless really bad we are talking thousandths of an inch. Scratches from stacking and cutlery I would think often more noticeable for regular daily wear. 

[Mark C.]

No matter how hard I look at my stoneware (Daily) use plates from 1976 they are still tough/smooth as nails with a semi Matt glaze on them. They go into a dishwasher near daily as well. Same with mugs and bowls -I think all my  daliy dishware has 30-45 years on it. The stoneware has a few chips on feet as it not as tough as the porcelain.

[Bill Kielb]

1 hour ago, Mark C. said:

No matter how hard I look at my stoneware (Daily) use plates from 1976 they are still tough/smooth as nails with a semi Matt glaze on them.

All my old wares including mugs have lots of wear on them. Unless it’s brand new, stacking alone does a nice job of scratching everything. Whether production or hand made they wear. You are very fortunate.

[Mark C.]

Bill as you can see I take Great care in padding them-just kidding-heck they are stacked to the moon with no padding-mugs on top of one another

plates same way-Mugs are cone 10 stuff by other potters mostly

Edited June 9, 2022 by Mark C.

[oldlady]

mark, i see that you have enough for a great party.  when should we all come out?

 

ps  do i recognize the tiny one at the very bottom with your huge plates??

[Mark C.]

Yes that is one of your pots you gave me (Or we traded?) we use it pretty often as it perfect size for small things

Love the dragonfly image as well

[Mark C.]

I posted a better plate photo as the 1st one I took was to dark

[fweferfrrf]

I have two questions please guide me about this. These questions are shown below here:

1. https://community.ceramicartsdaily.org/topic/17153-gosloto-pqotw-week-41/
2. https://community.ceramicartsdaily.org/topic/28020-lunchtime-sustainability-in-your-ceramics-practice-survey/
 

Waiting for best answer as soon as possible. I am too confused here.

[PeterH]

Simply posting a link to another thread isn't a question.

The first link is to a quiz on kiln design terminology. The answers are in the first post in that thread! But the answers can also be deduced from the majority guesses given in the replies.

The second link is to a survey request on "sustainability in your ceramics practice" that doesn't seem to have generated a significant number of replies (probably because it was far too open-ended). Hard to see what the question could be.

This thread is about "dishwasher and microwave safe pottery".