Glaze inside only —-- Half outside help

[Nicky S]

Ps ….Just wodering  If I just glaze the inside of small earthenware bottles and half the outside Will they still be food safe and fully functional for storing oil ?
Thank you Nicky 

[Callie Beller Diesel]

You can do this with caveats, but even if all of those are fulfilled, it’s not ideal.

If you’re making a few things for yourself, it’s all in what you’re willing to accept in terms of mechanical suitability and how you use the piece. I personally would not do this for commercial sale. If something goes wrong, people will have something a bit gross on their hands. 

If you’re working with a porous clay body that will be holding oil, you need to really make certain the glaze fits well and doesn’t craze at all. If the glaze is crazed,  oil will seep through the crazing lines and into the clay body where it’ll go rancid over time. If your glaze fits well, you’ll have to make sure the glaze goes far enough down the outside of the pot to make sure the tension the glaze puts the clay under doesn’t crack the piece. I would do some thermal shock tests on a partially glazed cup  to make sure everything’s durable before committing. 

This would be an easier project if you were to use a stoneware or porcelain that had less than 1% porosity when fired. I’d still be a good idea to have the well fitted glaze that went part way down the outside of the pot as well.

 

[Chilly]

I have bathroom air fresheners like that. 

No glaze on inside, glazed bottom and halfway up sides. 

Commercially produced.  White clay. 

Every year or so, I put them into a bisque load to burn off the staining from the air-fresh liquid.

Wouldn't want anything like that for food.

[Nicky S]

On 12/12/2021 at 4:20 PM, Chilly said:

I have bathroom air fresheners like that. 

No glaze on inside, glazed bottom and halfway up sides. 

Commercially produced.  White clay. 

Every year or so, I put them into a bisque load to burn off the staining from the air-fresh liquid.

Wouldn't want anything like that for food.

Just a thought and idea :-)

[Nicky S]

On 12/10/2021 at 9:00 PM, Callie Beller Diesel said:

You can do this with caveats, but even if all of those are fulfilled, it’s not ideal.

If you’re making a few things for yourself, it’s all in what you’re willing to accept in terms of mechanical suitability and how you use the piece. I personally would not do this for commercial sale. If something goes wrong, people will have something a bit gross on their hands. 

If you’re working with a porous clay body that will be holding oil, you need to really make certain the glaze fits well and doesn’t craze at all. If the glaze is crazed,  oil will seep through the crazing lines and into the clay body where it’ll go rancid over time. If your glaze fits well, you’ll have to make sure the glaze goes far enough down the outside of the pot to make sure the tension the glaze puts the clay under doesn’t crack the piece. I would do some thermal shock tests on a partially glazed cup  to make sure everything’s durable before committing. 

This would be an easier project if you were to use a stoneware or porcelain that had less than 1% porosity when fired. I’d still be a good idea to have the well fitted glaze that went part way down the outside of the pot as well.

 

@Callie Beller DieselNo this is definitely not for commercial use. Thank you so much for your explanation and advise. *** Quote ( If your glaze fits well, you’ll have to make sure the glaze goes far enough down the outside of the pot to make sure the tension the glaze puts the clay under doesn’t crack the piece. )**
For arguments sake ( use bottle as a vase now and fill only with water ) If only the inside is glazed and outside left unglazed . Is there an even higher risk of  tension cracking ? Or other problems Thank you Nicky

[Bill Kielb]

43 minutes ago, Nicky S said:

If only the inside is glazed and outside left unglazed . Is there an even higher risk of  tension cracking ? Or other problems Thank you Nicky

To answer your question, maybe not higher but a risk, yes. We see this happen on occasion with coffee mugs only glazed inside. Not often, but it does happen where the user pours hot coffee in it after using it many many times and suddenly the mug shatters. It’s sort of rare, but unpredictable and with hot coffee it scares most enough to try and never do it or at leas glaze partially down the outside to keep tension relatively even.

[Nicky S]

1 hour ago, Bill Kielb said:

To answer your question, maybe not higher but a risk, yes. We see this happen on occasion with coffee mugs only glazed inside. Not often, but it does happen where the user pours hot coffee in it after using it many many times and suddenly the mug shatters. It’s sort of rare, but unpredictable and with hot coffee it scares most enough to try and never do it or at leas glaze partially down the outside to keep tension relatively even.

@Bill KielbThank you …. So much to learn and think about 

[Callie Beller Diesel]

Having mugs unglazed on the outside was definitely a trend a few years ago, and I did buy a few from folks that made really beautiful ones. I’ve never had one shatter, but almost all of them got u shaped cracks coming down from the rim eventually. 

[Mark C.]

Galze on the inside and only partial on the outside can weaken the pot-it all deoends on the clay body and the two glazes and the tension it can or cannot put on them.

With oil as the function it seems a poor choice for me my thats just my esthetic I'm all about the most long lasting and strongest functional wares.

Of course I have sold thousands of pots in my  nearly 50 year career  and have seen a few go bad.  so I always start with making them as tough as I can and fully glazed is one of those components ..

 

Bill I had a potter friend in the 70s who used funky clay and fired it all in a oil fired salt kiln. I poured hot water in two of his mugs one day and they both just cracked apart. He was a funk potter and the wares where not able to handle hot water expansion.

In terms of oil in a pot well that use will test the ware well especailly 1/2 glazed

[Nicky S]

On 12/13/2021 at 9:49 PM, Callie Beller Diesel said:

Having mugs unglazed on the outside was definitely a trend a few years ago, and I did buy a few from folks that made really beautiful ones. I’ve never had one shatter, but almost all of them got u shaped cracks coming down from the rim eventually. 

As you said “ eventually “ :-) But yes get your point … Thank you Nicky

[Nicky S]

On 12/10/2021 at 9:00 PM, Callie Beller Diesel said:

You can do this with caveats, but even if all of those are fulfilled, it’s not ideal.

If you’re making a few things for yourself, it’s all in what you’re willing to accept in terms of mechanical suitability and how you use the piece. I personally would not do this for commercial sale. If something goes wrong, people will have something a bit gross on their hands. 

If you’re working with a porous clay body that will be holding oil, you need to really make certain the glaze fits well and doesn’t craze at all. If the glaze is crazed,  oil will seep through the crazing lines and into the clay body where it’ll go rancid over time. If your glaze fits well, you’ll have to make sure the glaze goes far enough down the outside of the pot to make sure the tension the glaze puts the clay under doesn’t crack the piece. I would do some thermal shock tests on a partially glazed cup  to make sure everything’s durable before committing. 

This would be an easier project if you were to use a stoneware or porcelain that had less than 1% porosity when fired. I’d still be a good idea to have the well fitted glaze that went part way down the outside of the pot as well.

 

Thank you so much for your input Nicky

[Nicky S]

On 12/14/2021 at 4:33 AM, Mark C. said:

Galze on the inside and only partial on the outside can weaken the pot-it all deoends on the clay body and the two glazes and the tension it can or cannot put on them.

With oil as the function it seems a poor choice for me my thats just my esthetic I'm all about the most long lasting and strongest functional wares.

Of course I have sold thousands of pots in my  nearly 50 year career  and have seen a few go bad.  so I always start with making them as tough as I can and fully glazed is one of those components ..

 

Bill I had a potter friend in the 70s who used funky clay and fired it all in a oil fired salt kiln. I poured hot water in two of his mugs one day and they both just cracked apart. He was a funk potter and the wares where not able to handle hot water expansion.

In terms of oil in a pot well that use will test the ware well especailly 1/2 glazed

See how it works …. Tho might just change oil and use water (? ) ie for use as a vase And thank you for commenting Nicky