Bizen yaki leak

[Drax]

I recently picked up a Bizenyaki mizusashi, and it has a very slight leak somewhere near the bottom.

Will the boiling and/or cornstarch method for hagiyaki work the same for bizen...? Or...?

[Chip]

I can think of one way to find out ...

[Drax]

I can think of one way to find out ...

Indeed!

Perhaps, then, I should ask a second question first. Is it safe to boil Bizen?

I would think so, given the firing temps.

However, I put in some boiling water to do a quick rinse when I first got it (it had some fuzzies inside), and when I added the water, I heard a horrifying "crack" sound -- rather like when ice cracks, but more metallic.

Anyway, I stopped adding water and decided that was enough...

[Chip]

I was thinking the cornstarch method!

[Drax]

Ah, I was thinking you still needed to boil for the cornstarch method... I will give that a go.

Though I might need some cornstarch first. D'oh!

[Tead Off]

Ah, I was thinking you still needed to boil for the cornstarch method... I will give that a go.

Though I might need some cornstarch first. D'oh!

I recall a bizen vase that I bought off ebay from Katsuragi that leaked. Theoretically, it shouldn't have because of the high firing but maybe kiln placement or insufficient firing may have caused this. I used the cornstarch method, rice method, tea method, prayer method , nothing stopped it, just lessened it to the point where it doesn't leak but weeps over a couple of days and will develop a wet spot wherever it sits. I got my money back from Katsuragi but if yours doesn't stop after treating it, I would ask the seller for a refund. They shouldn't leak at all and this being a mizusashi, personally would drive me crazy as I use one all the time for my tea water.

[Firebug Pottery]

This crack that you heard is what us potters refer to as a "dunt" this is caused either by a high amount of cystobalite, which is a polymorph form of silica, or a deficiency in silica in the clay body. The local clays I use here are silica deficient, and I have heard that sound many times before I learned how to correct it. I always pour boiling water in mine before I send them out just to test, but some do it later on. The potter should either reimburse you, or replace the piece, as it is an unfixable fault.

Good luck,

Jayme

[JBaymore]

However, I put in some boiling water to do a quick rinse when I first got it (it had some fuzzies inside), and when I added the water, I heard a horrifying "crack" sound -- rather like when ice cracks, but more metallic.

Drax,

Firebug pretty much gave you the answer there. Unfortunately it sounds like the differnetial thermal stress you developed between the hot interor and the colder exterior caused the body to fail. If you look very carefully, you should see a faint hairline crack somewhere now.

Mizusashi are larger sized objects and such stresses that are able to be withstood in a smaller piece sometimes cause larger ones to let go. In this case it is called a case of "delayed dunting". The stresses were there in the clay form already, but the boiling water pushed it over the edge.

The clays used in many Japanese pottery centers are often very simple compositions. Sometimes a single naturally occuring clay, and many times blends of at most a couple of different natural clays. Frequently they are low on fluxing materials to cause the silica present in the clay body to actually melt and go from the cyrstalline phase to the glassy phase. (Modern industrial type bodies are formulated to address this kind of issue, amongst others.)

At elevated temperatures, as Firebug mentions, the crystalline form of silica converts from one form to another. The rate of conversion is related to both time and temperature.... so multi-days long anagama and noborigama type firings are prione to developing the issue with certain clays.

The cristabolite form of SiO2 has a higher reversible coefficeint of thermal expansion than "normal" SiO2 does, (the glassy phase is non-crystalline and does not exhibit this) and it casues strresses in the body as the kiln cools. Oftentimes, the pieces with high cristabolite levels crack during uneven cooling in the kiln and emerge broken. Sometimes, the problem only shows itself when additional stresses are added.... like your boiling water.

As to the original leak........ it might have been a case that the piece had a slight dunting crack in it to start with..... that the potter missed in his/her quality check...... and your boiling water caused the crack to "run".

I would expect that the supplier/potter will replace the piece or refund your money. Too bad. Be glad that it was not sitting on an expensive Steinway grand piano when it let go .

best,

.........john

[Drax]

Ah, I was thinking you still needed to boil for the cornstarch method... I will give that a go.

Though I might need some cornstarch first. D'oh!

I recall a bizen vase that I bought off ebay from Katsuragi that leaked.

Hm, I got this mizusashi from Katsuragi as well. Must be a coincidence.

Jayme and John -- thanks for the detailed info, that's really cool! (well, scientifically cool, not practically cool, heh).

Fortunately the mizusashi was on top of my microwave when I discovered the leak. Also fortunately, it's a pretty minor leak (I'd say about 2 mL per day or so?). Given that I find this vessel otherwise perfect, I am going to attempt to cornstarch it.

Hey Chip -- are there any recommendations on cornstarching? That is, how much cornstarch in how much water, how long, etc?

[Chip]

It has been a while since I had to CS a piece. We discussed it at length in the Hagi topic I think ... I will do a search.

[Drax]

Thanks, Chip. I looked at that discussion, and best I could find was talk about 'hot and cold' treatments and nothing too more specific.

So I just went ahead and dumped in some cornstarch with some hot (not boiling) water.

On the plus side, my problem is solved. I dropped it while emptying it, and it shattered-- aww, I'm just kidding, I didn't drop it. Actually my first treatment of hot water and cornstarch appears to have worked, it's not leaking anymore. I rinsed it out, and refilled it, and it's not showing any signs of a leak.

However.... I do have a new concern.

This mizusashi has a very bold red stripe or two on its underside, which also appear on the interior of the vessel. When I refilled the mizusashi with cold water, I noticed some red bits floating on the water -- yep, some of the material of one of the stripes is coming off.

I suppose I shouldn't be surprised since the interior isn't glazed. I am going to assume that it will not be too healthy to swallow the red stuff.

So one last (I hope) question -- should I try to dislodge the major bits on the inside? Or just rinse it out a couple more times and simply fish out any floaties I find...?

[Chip]

That is good news about the CS treatment! You may need to repeat this at some point ... as the CS can sort of work its way to the exterior.

Not sure where that discussion was ... I looked too.

I am guessing rinsing would be sufficient for the dislodged particles ... but what do I know.

[JBaymore]

Drax,

The "red stripes" on Bizenyaki likely are from a technique called hiduski. The stripes are formed when rice straw is wrapped around the high iron bearing clay piece and then the wrapped portion of that form is protected from the general circulation of gases in the kiln, often by placing that protion inside another pot or in a saggar (special kiln furniture container).

It is cause by a chemical reaction between the chemicals in the ash from the rice straw and the silica and iron from the clay body. It can be very striking and beautiful. (These types types of pieces are also often fired in either gas or electric kilns these days.)

It is spossible some of the rice straw ash that is on the surface that was not tightly bonded is flaking off. Likely this will stop soon.

If this is the source of what you are seeing, I'd not worry too much about any possible toxic properties....... just "aesthetic issuses" in consuming the material.... and the possible "gritty bit" happening on the teeth.

best,

..........john

[Robert Fornell]

Here'sa bit more on hidasuki....

http://sciencelinks.jp/j-east/article/2 ... 04447.phpa bit more one hidasuki.

Best,
R

[shyrabbit]

Interesting conversation...would it be possible to see an image of the piece in question?
Michael