My dinnerware keep makes crazes on surface.

[Heetter]

Hi! I have some problem to make dinnerware. Firstly sorry for my English is not so good.  I am making ceramic for food container like cups or dishes. I tried 2 brand of hand paints which has different range of firing temperature. 
Duncan and Amaco. Use Duncan in1001 transparent glaze. I prefer to use Duncan because the result of colouring was best. 

But problem is I use claybodies which need to fired at 1250 celsius degrees, but the paint and glaze’s recommended firing temperature is much lower. 
I can’t change the clay bodies because in my country low temperature fired claybody is very uncommon, I can’t get them. 
well, result of colour by Duncan is so nice but most of pieces makes very thin crazes like spider web on surfaces, and Its goal usage is food container, but when it meets water, making crazes faster with sounds. Some are making crazes over a months. Also that craze tent to be made more on certain colour like blue. I found that usually on red paints, there’s less craze.
More problem of when claybodie fired not enough to mature, I could see it absorbs water a bit. 
So I tried to fire them on temperature for mature claybodies, then colour of Duncan paints is totally changed as very ugly! 
i am still on experiments but really can’t find any clue. I read article about it, clay and glaze’s shrinkage rate is different so it makes crack.

I rescheduled firing, I reduce half of time on hightemperature, conclusion was it makes less crazes but still does makes craze.
I saw many potter in Korea, use that clay and paints they still makes well looking dinnerware. 
but can’t find solution of this. 
so what I want to know is

1. Not fully fired clay can’t be use as dinnerware? (It haven’t to meet water? Only for objects) 

2. How to control shrinkage rate of clay or glaze? 
3. Its better to suit clay to glaze because painting colour will be changed on higher temperature, then what should I change on process? 
 4. Is there any method that could I use both of Duncan glaze and high temperature claybodies without making craze? 

I fire ceramics literally everyday now for months, still don’t have any clues. Please help me! 
 

[Bill Kielb]

Sounds like you have a midfire clay cone 6-8 and you are trying to use lowfire, cone 06 glaze and underglaze products. Post information on both clay and glazes you are trying. Please include the manufacture and number of each posted so we can identify exactly what these products are and their firing ranges.

[Heetter]

Thanks for replying! 
I am using claybodies which could fire cone7 to 8, stoneware clay! Which made in Korea, the colour of clay is dark brown (like as mud) when it’s not dried, when its dried fully colour is light grey.  Sorry that I can’t change clay because can’t get lowfire clay. 

For underglazes I am using Duncan CN/CC underglaze. It says can be fired at cone 5 to 10. But when I fired them on cone7, mostly colour are very different (green colour changes to brown), or some are just disappeared. 

Glaze what I use is also from Duncan IN 1001, it’s appropriate firing temperature is cone 06. 
 

For bisque firing, highest temperature is 1472 f degrees, and I fire 1830 f degrees for second time. Then result always has craze. (Sorry that I am too confused about words for cone temperature) 

otherwise when I fire cone 7 for second fire,  underglaze colours are totally turned. And drawings are smudged. 

I do hand painting and put glaze by brushing, but really there’s no substitute glazes here. Materials are optimized to pouring way.  So that’s why I am still not changing materials...  Hope there’s some method for solving this problem. 
 

ah! There’s one more question! I saw topic that when fired at lower temperature than mid-temperature, every glaze has risk to use as for food container whether it says safe for food or not. But Duncan what I use, it’s low fired glaze, but is indicated as safe for dinnerware. I am confusing, because I plan to make dinnerware for sale, I want to make safe one. 
 

sorry again for my poor English. Xoxo
 

[Hulk]

Hi Heetter!

My guess, next step for discussion here, confirming/clarifying the temperatures?

Your stoneware clay matures at cone 7/8, ~2300F ?

You are bisque firing to 1472F (cone 015)?

You are glaze firing to 1830F (cone 06)?

For dinnerware, likely you'd want to fire the clay to full maturity, hence, change clay to match the glazes you have, else, obtain glazes that mature at about the same cone as the clay you're using.

[Bill Kielb]

So assuming you are stuck with your clay you will need to find a glaze that fires more closely to your claybody maturing temperature. Since there are many cone 6 glazes commercially it would be nice to fire your clay to cone six and see if the outcome is sturdy enough. If yes, then you can simply find cone six glazes that do not craze.

As far as underglaze goes, some retain colors better than others as well as some colors fade or darken excessively the higher temperature you fire.

There are still possibilities here as in firing one cone lower with a 15-20 minute hold to still reach the next cone. So for instance if your clay was sturdy and relatively non porous at cone 7 then you could try using cone six product firing to cone six with a 15-20 minute hold. This should get you close to firing to cone 7 without actually having to reach that peak temperature which for many can preserve colors from fading or darkening.

Anyway, this is getting way too long, but don’t despair, find glazes that work nearer cone 7/8 and you will find underglazes that will also. I have done a fair bit of this work and have included some example pictures where color and temperature needed to be just right so most of the pieces below were the result of testing with exception of the mug. The mug was created with cone six clay and fired to cone six with a base (Blue) glaze  and then refired several times using Mayco stroke and coat and fired to 06. The stroke and coat fires from cone 06 on up to cone 10.. the dragon was created by multiple firings at 06. It’s another possibility.

In addition, note the test palette of underglaze or stain colors fired to cone six to see how well they retain their color at the top firing temperature.

I hope that gives you some ideas, but you will very likely need to find glazes that fit your clay body which means more like cone 6 glazes. Testing colors for fading / darkening is just something that many do.

[Heetter]

Thanks for replying again! I am making test palettes for now. what colours of underglaze should endure high temperature with glazes that has different firing temperature range. 
If out come isn’t satisfied maybe I should change some materials. I will share the result on this page so ppl who has same problem could get substitute way. Thanks for helping me  out