Jump to content
Sign in to follow this  
Tenyoh

Water Seeping Through

Recommended Posts

I'm making ikebana vases and having a problem with water seeping out the unglazed bottom. As I thought the clay vitrification was the problem, I fired the second batch one cone higher - to cone 6. (The firing range of stoneware I used was cone 06-6.) After the firing, I poured water into the vases and waited overnight. To my disappointment, water still weeped through.

I read in your former topic, "If the glaze crazes, then liquids can seep through the cracks in the glaze and into the wall of the pot, and weep out the unglazed bottom." Amaco Potters Choice glazes I used do not look crazed, but it must have been. Are there any special way to glaze inside a vase, so that it will not craze? (I put a tiny bit of water into the glaze and spread it inside the vase.) Do you recommend any particular commercial glaze for this purpose? Does glazing the bottom slow the seeping significantly?

So far, I've been solving the problem, sealing the cracks with liquid waterseal for wood. However, I worry the effect may last only temporarily. Do you have any idea how long the effect of such sealant will last?

Thank you for your expertise in advance.

Share this post


Link to post
Share on other sites

A problem I have had too.

 

What I have found is bigger pieces and thicker bottoms were weeping. Smaller pieces and thinner bottoms weren't.

 

My logical explanation is thicker bottom centers aren't getting fully vitrified because it would take extra time for the heat to reach them. This thicker but more porous bottom ends up weeping.
 

My solution has been to trim the feet.

Share this post


Link to post
Share on other sites

Thank you for your responses. As Mark C.'s answer was interesting, I called the clay manufacturer. They said even though the clay had the broad range, it should not affect the vitrification. "Even cone-10 clay will seep after awhile." "You have to seal with glaze." Their answer confused me about the vitrification. They recommended to hold the kiln for 10 minutes to seal the crazes and pinholes. Even though I don't see them, they must be there.

 

MathewV, have you experimented with holding the kiln?

Share this post


Link to post
Share on other sites

I have an idea for checking for crazing. Take some EPK or any light clay, mix in water, and soak inside the pots for a few hours. Pour it out, and let it try -- if you see white crackles in the glaze then you know the glaze has crazed.

Share this post


Link to post
Share on other sites

I'd find a new clay manufacturer and clay body. A properly vitrified clay fired to maturity should be water tight without glaze. Only an underfired/non-vitrified clay body weeps. Sounds to me as if they do not know their product or are unwilling to admit their product is faulty. Find a cone 6 clay body with less than 2% absorbency. Then you will not have to rely on glaze to make the vase water tight. A clay manufacturer stating that glaze is needed to seal the clay body is just plain out to lunch.

 

I make and sell ikebana vases; my cone 6 vases are made using cone 6 clays (Little Loafers and Red Rock from Highwater; occasionally 266 from Standard) and fired to cone 6 with a 10 minute hold. I chose those because they have low absorbency at Cone 6. My cone 10 vases are made using cone 10 clays (Laguna's Dark Brown, Standard's Troy wood fire stoneware or porcelain, or Highwater's Phoenix) -- clay bodies with absorbency of 1% or less at cone 10. I use a liner glaze -- sometimes clear, sometimes another color glaze. Most of mine are only glazed on the inside. I also randomly pull vases and test them with water. I've had vases sit on my table with water/flowers for two or more weeks with no weeping.

Share this post


Link to post
Share on other sites

I totally and completely disagree with what your supplier said. Load of rubbish. Pots that are meant to be watertight must not leak even when there is no glaze on them whatsoever. A 10 minute soak is going to do diddly squat to the absorption of a ^6 clay being under fired.

 

Like Mark and Bruce said get a clay that matures at the cone you are firing to. A water tight low fire clay is going to be hard to find. Most clays list their absorption rates, look for one under 2%. (some clays are okay a bit higher than this) Make some test pots by making flat based cylinders, scatter them throughout the kiln, some in the middle of the kiln to allow for thermal lag there. Fire the pots to the proper cone with no glaze either inside nor outside.  Fill them with water and put them on a couple sheets of newsprint for a week. There should be no wrinkles in the paper after that time. I make a lot of French Butter Dishes, water is in the base of them 24/7, just like vases they need a tight body. Once you find a clay that works I would re-test it when you get a new batch of it to be doubly sure.

Share this post


Link to post
Share on other sites

The clay manufacturer's catalog does not even list the absorbency of clays they sell. Yes, I will look for another supplier and test the clay as Min suggested. Thank you very much.

 

 

I have an idea for checking for crazing. Take some EPK or any light clay, mix in water, and soak inside the pots for a few hours. Pour it out, and let it try -- if you see white crackles in the glaze then you know the glaze has crazed.

Douglas, I tried this method using ball clay. I may have used too much clay. When I dumped the water, it left streaks and lumps and it was difficult to see fine cracks. Thank you for your suggestion, though.

Share this post


Link to post
Share on other sites

I am firing Newcomb 6 (Clay Art Center) to the far side of cone 6. (1220°C with a 5 minute hold and a slower ramp rate in the last 100°C and then cooled at 120°C/hr). So, yes, I have experimented with the program and am completely satisfied with my kiln doing what it is asked.

 

Here is what the Clay Art Center says about this clay:

"An off-white/gray tile CLAY body that is also used for throwing and pressing sinks and large items. A large amount of grog keeps warping to a minimum, yet the small size of the grog does not affect the fired surface. Extruded tiles up to 2 square feet are possible with this clay body. Bisqued 6 x 6 tiles are available. This is a good production clay body with excellent glaze fit. Cone 4-6.  Wet Color tan, Oxidation Color off-white/tan, Reduction Color light brown, Texture medium smooth, Shrinkage 12.0%, Absorption 2.06%"

 

 

And I have piece that weep and pieces that do not. The common quality of the weeping ones is slightly heavy bottoms.

So after I started to trim the feet... no more issues!

Share this post


Link to post
Share on other sites

Here's a similar test to what Douglas suggested: Fill the vase with a mixture of vinegar and Whiting (it will bubble) and let it stand overnight. The Whiting and vinegar react to form calcium acetate, which is soluble, so will migrate into the body if it allows water to seep through. After you empty the vase, the calcium acetate will slowly migrate to the surface as the body dries out, and will concentrate along any craze lines.

 

I haven't used this intentionally as a test for crazing myself, it's just something I noticed after using a bowl with non-obvious crazing to mix Whiting and vinegar.

Share this post


Link to post
Share on other sites

Thank you, MathewV, for the info. Yesterday I epoxy-glued decorative feet on the bottom of the vases and then tested for the weeping again. (As I had anticipated the problem, I had made the feet at the same time with the vases.)  Ventilation of the dry South Dakota air seemed to have helped. The bottoms felt cool to touch, but not wet this morning. I put small pieces of folded paper under the vases between the legs, to see if it will get damp by this evening.

 

I learned a lot in this post. Thank you very very much.

 

 

Here's a similar test to what Douglas suggested: Fill the vase with a mixture of vinegar and Whiting (it will bubble) and let it stand overnight. The Whiting and vinegar react to form calcium acetate, which is soluble, so will migrate into the body if it allows water to seep through. After you empty the vase, the calcium acetate will slowly migrate to the surface as the body dries out, and will concentrate along any craze lines.

 

I haven't used this intentionally as a test for crazing myself, it's just something I noticed after using a bowl with non-obvious crazing to mix Whiting and vinegar.

 

I don't have Whiting. Do you think I can substitute it with baking soda? Mixing it with vinegar will certainly bubble.... It may be fun to test it. Thank you for the info.

Share this post


Link to post
Share on other sites

Thanks for the ideas for the household item substitutes. I have toothpaste and epsom salts. I'll give them a try.

 

You all are with full of ideas and expertise. I feel heartened. Thank you so much.

Share this post


Link to post
Share on other sites

Have you tried firing it even hotter than ^6? Like up to ^7 even though it's a ^6 clay?  IMO it's worth a test (use a waste tray/shelf underneath just in case)

 

You mention you "can't see any crazing"....to a molecule of water or a tiny bacteria, a teeny tiny fissure in the glaze is like the grand canyon, of course it will make it's way through!

If your glaze is crazed, the glaze and clay body do not fit one another, their coefficient of expansion is too dissimilar.  This is only part of your problem, the other seems to be lack of vitrification in the clay itself.  For those experiencing seeping on thicker forms - this is because the thicker it is, the more heat work it requires to penetrate the core of that clay mass and bring it to full maturity - which is why reducing thickness via trimming the foot resolved the problem.

 

To test if your clay is vitrified: fire object and then weigh it.  soak in water for 24hrs, dry it off as best you can and then weigh it again.  calculate % of absorption from the difference.

Share this post


Link to post
Share on other sites

Glad I can access to this forum today. I did the tests suggested by you.

 

Re: Crackles

A test with Epsom Salt did not work (I dissolved the salt in hot water and then added an equal amount of vinagar), but it worked with lime stone. Crackles I saw were so superficial that they disappeared once I wiped the powder. They must go zigzag through the glaze all the way to the clay surface. Hopefully a 10-minute hold will solve this problem.

 

Re: Vitrification

I tested with an unglazed chunk of clay that had been fired to cone 6. The absorption level was 4.4%. Percolator, you recommended to fire the clay to cone 7. I wonder if it's worth trying it, knowing the clay mixer's suggestion of glazing inside. As I want to leave my vases unglazed like some of you are doing, I'm thinking of trying clays from an established clay manufacturer. Have any of you used Laguna's, especially the following brown clays:

 

WC394 SB Red, absorption 2%

WC420 Redstone, absorption 0.5%

WC866 Electric Brown, absorption 0.5%

 

As I have to drive 5~6 hours to get to the nearest Laguna distributor, I intend to purchase a few different ones and experiment with them.

 

Thanks again.

Share this post


Link to post
Share on other sites

Besides seeping, what else problems do you anticipate with absorbent clays? I was going to make something like yarn bowls and spoon rests with that clay.

Share this post


Link to post
Share on other sites

If firing low, you may be able to glaze all over and place pieces individually on stilts(?) spurs with some success.

Yarn bowls, well let's hope there is no wet wool.

Spoonrests are usually in the kitchen area on wipable surfaces,, not sitting with moisture in them on precious surfaces usually, so would be ok imo even without the glaze and spur treatment.

Share this post


Link to post
Share on other sites

It seems high absorbent clays are not ideal for most of the functional ware (provided there are wet wool  ;) ). I'll keep that in my mind from now on.

 

Mark C, I am considering to mail-order Laguna clay. All I need for now is a box. That should work.

 

Thank you all again for your input. 

Share this post


Link to post
Share on other sites

I have found that with a cone 6 clay body fired in a digitally controlled kiln, dropping 100 degrees and holding for one hour will even the firing a bit but mostly the clay continues to vitrify without over firing the glaze. Cone 5/6 is such a mid range stoneware that vitrification can be tricky in an uneven kiln.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

By using this site, you agree to our Terms of Use.