[Ginny C]

I've just discovered that two vases I've made from a cone 5-6 stoneware clay are slowly leaking onto the table!

Both were glazed inside, dry-footed. Fired to cone 6. The glaze appears to be thin in some spots near the bottom inside. Is this why water is slowly leaking through?

Should I refire them with additional glaze inside? With enough glaze inside should pots be safe to use as vases?

Thanks for any help!

ginny c.

[JBaymore]

Ginny,



Its that clay body listed as cone 6 to 10 clay? If so... you have your answer as to the cause of the issue. At 6 it is not vitreous.

If it is truly a cone 5-6 clay... then "something is up" and we can go further.


best,

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

[OffCenter]

Ginny C, on 08 October 2012 - 10:55 PM, said:

I've just discovered that two vases I've made from a cone 5-6 stoneware clay are slowly leaking onto the table!

Both were glazed inside, dry-footed. Fired to cone 6. The glaze appears to be thin in some spots near the bottom inside. Is this why water is slowly leaking through?

Should I refire them with additional glaze inside? With enough glaze inside should pots be safe to use as vases?

Thanks for any help!

ginny c.

The important thing is what John said above, but I want to add that you should not depend on the glaze to stop a leak. Your vase should not leak even unglazed. Even when the crackle is too fine for you to see, it is there in most glazes and that is all water needs to seep through. The glaze may slow the leak but in almost every case will not stop it.

Jim

[Ginny C]

JBaymore, on 08 October 2012 - 10:21 PM, said:

Ginny,



Its that clay body listed as cone 6 to 10 clay? If so... you have your answer as to the cause of the issue. At 6 it is not vitreous.

If it is truly a cone 5-6 clay... then "something is up" and we can go further.


best,

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

It IS clay for one 5-6, for sure. I don't have the box here so I cannot tell you the specific clay, but I know it is cone 5-6. I made these items in a pottery studio in Michigan, where all the clay is that kind and it is always fired to cone 6.
They are bisque fired to cone 04 and then glaze fired to cone 6.
Thanks for any help!
Ginny

[clay lover]

I have had the exact same thing happen, with Highwater Ellen Buff, rated ^4-6, Slow seeping onto a shelf. I bisqued to ^04, glazed, with cones for verification to a solid ^6. They were fully glazed inside and out, even glazed inside the foot ring.
Haven't a clue what's up.

[OffCenter]

clay lover, on 09 October 2012 - 10:50 AM, said:

I have had the exact same thing happen, with Highwater Ellen Buff, rated ^4-6, Slow seeping onto a shelf. I bisqued to ^04, glazed, with cones for verification to a solid ^6. They were fully glazed inside and out, even glazed inside the foot ring.
Haven't a clue what's up.

I have a clue to what's up. The clay doesn't vitrify at cone 6. The glazing is irrelevant. I'd try testing it unglazed fired to cone 7 and 8 and let Highwater know they need to change Ellen Buff or correct the misinformation about its cone rating.

Jim

[Michaelizabeth]

Ginny C, on 08 October 2012 - 09:55 PM, said:

I've just discovered that two vases I've made from a cone 5-6 stoneware clay are slowly leaking onto the table!

Both were glazed inside, dry-footed. Fired to cone 6. The glaze appears to be thin in some spots near the bottom inside. Is this why water is slowly leaking through?

Should I refire them with additional glaze inside? With enough glaze inside should pots be safe to use as vases?

Thanks for any help!

ginny c.

I had some of mine sweating water onto the table during the really hot months. Is it possible that's all it's doing?

[Edith Marie]

Ginny C, on 08 October 2012 - 07:55 PM, said:

I've just discovered that two vases I've made from a cone 5-6 stoneware clay are slowly leaking onto the table!

Both were glazed inside, dry-footed. Fired to cone 6. The glaze appears to be thin in some spots near the bottom inside. Is this why water is slowly leaking through?

Should I refire them with additional glaze inside? With enough glaze inside should pots be safe to use as vases?

Thanks for any help!

ginny c.

Good Morning Ginny,

Drinking out of glassware water seems to appear at the bottom. Try using coasters or dolies add a nice touch under a vase......

Edie.

[Phil in AZ]

Stoneware clays are not completely vitreous. If the clay is not fire up to it's proper temp, that can increase it's porosity. So a cone 6 body that only reaches cone 4 is more porous. Also, if there is a glaze flaw, you can get leaks. The thin spots you described could be the problem but a glaze that doesn't 'fit' the body, meaning there is some crazing (cracking in the glaze), may be the problem. You might try re-glazing the interior and firing the piece again which may or may not help. Also be aware that putting a really really thick amount of glaze in the interior can exacerbate the crazing issues. In this case, more is not better, The correct application is better. So fire it again an see what happens. We learn from our errors.

[yedrow]

I would find a similar object that doesn't leak and tap it lightly against something solid but not extremely hard. Then tap the two vases. It may be that they have dunted a little, but not enough to be real visible. I've seen pots with hairline cracks that reveal themselves by leaking. Other than that, if you are using a common glaze that you know vitrifies at cone 6, on a body that you know is supposed to vitrify at cone 6, and they both look normal, it seems likely to me they are both vitrified. If it is a new clay on the other hand, you may need to talk to your supplier. As Jim said, glaze doesn't always produce an in impermeable barrier.

Joel.

[Mark McCombs]

Michaelizabeth, on 09 October 2012 - 08:29 AM, said:

I had some of mine sweating water onto the table during the really hot months. Is it possible that's all it's doing?

The hotter the air the more water it can contain.

With a cold liquid inside, it is possible that this is just condensation on the outside of the vase, cup, mug, or jar.

[JBaymore]

Phil in AZ, on 09 October 2012 - 11:51 AM, said:

Stoneware clays are not completely vitreous.

Good stoneware clays are basically approaching being fully vitreous. Apparent Porisity figures of less than 1% down to 0% is normal.

It is also possible theat there is a dunting crack (or some other crack) that is so thin tha it is almost impreceptibal to the eye that is causing the leaking.

Just because the clay is always fired to cone 5-6 does not mean that the forumlation actually is a cone 5-6 clay. It is highly likely that it is a cone 6-10 clay (which really does not exist). Many clay manufacturers do this to cut down on the number of bodies they have to stock... at the expense of either the cone 6 potters or the cone 10 potters.

best,

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



EDIT: Just notices that Joel already mentioned the possibility of a unseen crack. Good on ya'.

[GEP]

Ginny C, on 09 October 2012 - 10:15 AM, said:

JBaymore, on 08 October 2012 - 10:21 PM, said:

Ginny,



Its that clay body listed as cone 6 to 10 clay? If so... you have your answer as to the cause of the issue. At 6 it is not vitreous.

If it is truly a cone 5-6 clay... then "something is up" and we can go further.


best,

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

It IS clay for one 5-6, for sure. I don't have the box here so I cannot tell you the specific clay, but I know it is cone 5-6. I made these items in a pottery studio in Michigan, where all the clay is that kind and it is always fired to cone 6.
They are bisque fired to cone 04 and then glaze fired to cone 6.
Thanks for any help!
Ginny

Another important factor here ... just because the pottery studio in Michigan told you it was cone 5-6 clay, and told you they fired it to cone 6, that doesn't mean it's true. You really can't say that for sure unless you know the name of the clay and fired it yourself. Not calling anyone a liar, just that these kinds of mistakes are not uncommon.

Mea

[Mark McCombs]

All this talk is prompting me to make some test pieces.

I will make some extra cups and vases to test.

The clay body that I am using was designed by my friend and although it is generally catagorized as a ^5-6, I really don't know.

[OffCenter]

Mark McCombs, on 09 October 2012 - 02:32 PM, said:

All this talk is prompting me to make some test pieces.

I will make some extra cups and vases to test.

The clay body that I am using was designed by my friend and although it is generally catagorized as a ^5-6, I really don't know.

There you go! That's the first thing any potter should do before making functional pottery with a new clay body. It's not like it's hard to do. Just throw a small cylinder and fire it unglazed then fill with water and let it sit on paper all night. And, if it leaks, don't think you can fix it by glazing it. I'm surprised more potters aren't sued for ruined grand pianos and antique tables. Also, it hurts all potters to have someone telling her friends, "Don't buy handmade pottery. It leaks."

Jim

[KatzPots]

Can I get some clarification on this issue because I just found a similar problem.


I am using an earthenware clay that I bisque fire to cone 04 and glaze at cone 05, as recommended by the clay manufacturer. I put flowers in a vase and set it on my table. Today I picked up the vase and the table had a damp ring where the vase was sitting. Thus, my search on the forum for more information.

So what's the solution? Is the problem with the bisque temperature? Do I need to test the clay by bisque firing to a higher temperature and test for leaks, as suggested? I was not aware that I could not depend on what the clay company suggested as the proper firing temperatures.

I surely don't want to ruin any furniture! Thanks!

[OffCenter]

KatzPots, on 20 April 2013 - 11:04 PM, said:

Can I get some clarification on this issue because I just found a similar problem.


I am using an earthenware clay that I bisque fire to cone 04 and glaze at cone 05, as recommended by the clay manufacturer. I put flowers in a vase and set it on my table. Today I picked up the vase and the table had a damp ring where the vase was sitting. Thus, my search on the forum for more information.

So what's the solution? Is the problem with the bisque temperature? Do I need to test the clay by bisque firing to a higher temperature and test for leaks, as suggested? I was not aware that I could not depend on what the clay company suggested as the proper firing temperatures.

I surely don't want to ruin any furniture! Thanks!

Some clays shouldn't be used for vases, mugs or anything meant to hold a liquid because they don't vitrify and glazing those clays will not prevent leaks. I think you're going to have a hard time finding an earthenware that doesn't leak so you may want to consider using a higher firing clay for pots that hold liquids and, no, don't trust the clay company--test.

Jim

[AtomicAxe]

OffCenter, on 21 April 2013 - 12:04 AM, said:

Some clays shouldn't be used for vases, mugs or anything meant to hold a liquid because they don't vitrify and glazing those clays will not prevent leaks. I think you're going to have a hard time finding an earthenware that doesn't leak so you may want to consider using a higher firing clay for pots that hold liquids and, no, don't trust the clay company--test.

Jim

Exactly as Jim suggested, make a test unglazed piece and see not only if the water level drops in the piece (which indicates if the body is semi porous even if it doesn't fully leak) but tell you if it is even vitreous in the slightest.

clay starts to become vitreous somewhere around cone 1 but will still absorb liquid until that vitrification reaches about a 1-3% absorb rate and some may be rated for a cone 6 clay but still have anywhere between 6-20% absorb rate thus will leak. The clay will be mature at that temp, but some clays were designed for non-functional uses while others are.

That being said, when I get a new clay body there are three things I test ... shrinkage rate, absorbtion rate and glaze compatibility ... anything less and it is kind of pointless.

[KatzPots]

Thanks guys. This is just what I needed to know and suspected. I realize now that earthenware is too porous to use for anything that holds liquid for any length of time and now know that glazing won't change that. Good info.