What is the problem with slip cast yixing teapots?


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What is the problem with slip cast yixing teapots?

Postby ndw76 » Feb 20th, '11, 21:15

I recently read the thread which tells people how to tell if their yixing is slip cast. I discovered that all of my pots are slip cast. They have an ever so faint line down the center indicating that they were cast. Another give away was that the place I bought them from has many identical pots.

So that got me thinking, apart from each piece not being totally unique, what is the problem with slip cast yixing? Does it affect the quality of the tea?

Is slip cast tea pots only a problem for people who collect yixing for the sake of the the yixing and not the tea?

What do you think?
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Re: What is the problem with slip cast yixing teapots?

Postby edkrueger » Feb 20th, '11, 21:45

It makes the tea chalky and removes the flavor. These pots are a lot less dense.

I wouldn't be too sure that the line indicates slip cast. Yixing pots are constructed instead of wheeled, so there will be a line where the sides of the slab are joined. I suspect its should be basically invisible on high qualty workmanship pots, but some pots will have huge obvious lines on the inside.
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Re: What is the problem with slip cast yixing teapots?

Postby debunix » Feb 21st, '11, 01:53

Chalky?

Once the pot is fired, there's no more slip or slurry to dissolve into the tea, so I'm puzzLed by what you mean by "chalky" here. Can you explain a little further about what that means?
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Re: What is the problem with slip cast yixing teapots?

Postby tortoise » Feb 21st, '11, 10:03

I've had two slipcast pots that I broke in as if they were more valuable and they both tasted great. I gave one to a friend of mine and recently had some shui xian made in it and I was very impressed with how well the tea tasted. I realize that a real pot may taste even better. I don't own a real yixing at present, so couldn't say. All I know is that neither one of those two pots effected the tea negatively.

That said, there may be lead in them, or some other unknown characteristic that is bad -- but I think the only thing someone using a slipcast pot need worry about is overpaying for the them because they won't hold value like a hand made and some of the designs are a bit hokey that you will probably evolve out of liking.

I want to get into better pots, but these are the ones I have presently (gifts in both instances) and they work well for the time being.

Edit: I do have an inexpensive zhuni pot that does not appear to be slipcast, but I can't tell yet it's effect because I use it for a completely different tea with which I have little experience.
Last edited by tortoise on Feb 21st, '11, 11:16, edited 1 time in total.
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Re: What is the problem with slip cast yixing teapots?

Postby gingkoseto » Feb 21st, '11, 10:04

Actually I think many slip-cast teapots are more "glassy" and less absorptive than hand made ones. So the "patina" can be at the best surface accumulation, not inside out "glowing" of tea accumulation. In order to do slip cast, the clay mixture must be made semi-fluid to be poured into the mold.

I don't think there is anything ultimately wrong about slip cast pots as long as the prices are consistent with the quality. The potential problem is they are very different from hand made yixing (in clay texture as well as craftsmanship) but are sometimes sold for the prices of hand made yixing. I've seen some very high quality slip cast pots (the mold must be well made to make them). They are nice-looking and good to use, as long as one doesn't care that much about patina and doesn't expect them to be the same as hand made yixing. But many slip casts are made to feed lower-end markets.
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Re: What is the problem with slip cast yixing teapots?

Postby tingjunkie » Feb 21st, '11, 13:38

ndw76 wrote: I discovered that all of my pots are slip cast. They have an ever so faint line down the center indicating that they were cast. Another give away was that the place I bought them from has many identical pots.


These are not necessarily indications of slip cast pots. As edkrueger said, hand made and half hand made Yixing are made from joining slabs of clay together. I have a couple pots made with good clay that have very obvious seams on the inside- no big deal.

Also, I know there were a run of Yixing Factory produced slip cast pots made back in the 80's/90's which are supposedly great for making tea and sought after by Taiwanese collectors.

Moral of the story... if the pots works, and you like it, just keep using it and be happy! :wink:
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Re: What is the problem with slip cast yixing teapots?

Postby edkrueger » Feb 21st, '11, 17:58

debunix wrote:Chalky?

Once the pot is fired, there's no more slip or slurry to dissolve into the tea, so I'm puzzLed by what you mean by "chalky" here. Can you explain a little further about what that means?


Well, one thing, I think a lot of slip cast pots tend to be under fired and just because something is fired, even high fired, does not mean there is nothing to flake off into the tea –think Terra-cotta pots. Regardless, I taste this.
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Re: What is the problem with slip cast yixing teapots?

Postby bagua7 » May 8th, '13, 02:13

ndw76 wrote:Is slip cast tea pots only a problem for people who collect yixing for the sake of the the yixing and not the tea?


There is nothing wrong with them.

For further info see the following link (responses).
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Re: What is the problem with slip cast yixing teapots?

Postby Tead Off » May 8th, '13, 04:38

edkrueger wrote:
debunix wrote:Chalky?

Once the pot is fired, there's no more slip or slurry to dissolve into the tea, so I'm puzzLed by what you mean by "chalky" here. Can you explain a little further about what that means?


Well, one thing, I think a lot of slip cast pots tend to be under fired and just because something is fired, even high fired, does not mean there is nothing to flake off into the tea –think Terra-cotta pots. Regardless, I taste this.

Ed, I'm not sure if you literally mean 'flaking off' as in pieces of the clay falling into the tea. The definition of terra-cotta is generally low-fired and this could have a wide range of temps rendering some wares good for a very short time before they fall apart. Most terracotta will hold up for prolonged use.

When we move into high-fired territory, the tends to liquefy the clay to a point where there is nothing left to 'flake off'. The actual structure of the clay has been changed through heat.

Slip casting is old and has been used for a couple of hundred years. But the kind of collector teapots and drinker teapots that are sought after like zhuni are made from sand and ores and are processed in a way that gives a different result than clay processed for slip casting. Will we be able to tell the difference in taste? I have no idea.
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Re: What is the problem with slip cast yixing teapots?

Postby futurebird » May 8th, '13, 11:22

I have some cheap pots that are made of a clay that performs well brewing, but is much more brittle than higher quality yixing. This makes me wonder of they are slip-cast... yet they have all the marks of handmade or half-handmade: I can see where the spout and handles were smoothed in to place, I can see radial marks on the inside from joining and smoothing the bottom. Tiny knife marks in the base that indicate when it was removed etc...

I've decided they are hand made out of bad clay... kind of sad really since they are well-crafted!


Lastly, many clearly slip-cast pots I've seen have a dimple on the inside where the handle meets the body. --though some better slip-cast pot could easily hide this with hand finishing.

Slip casting can lead to an odd smoothness. As long as they are well fired, they can still be good pots.

I think if anyone tried to listen to all of the advice on this site your only option would be a 300-year old pot made by 5th grandson of LuYu under a blue moon.

:lol:
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Re: What is the problem with slip cast yixing teapots?

Postby JBaymore » May 9th, '13, 12:54

edkrueger wrote:
debunix wrote:Chalky?

Once the pot is fired, there's no more slip or slurry to dissolve into the tea, so I'm puzzLed by what you mean by "chalky" here. Can you explain a little further about what that means?


Well, one thing, I think a lot of slip cast pots tend to be under fired and just because something is fired, even high fired, does not mean there is nothing to flake off into the tea –think Terra-cotta pots. Regardless, I taste this.


Terra-cotta is a low fired product while the Yixing pieces are high fired. Different beasts. Every clay surface and every glaze surface (of all types of glass and ceramic wares) will tend to be affecting the water ("the universal solvent") ............... the question is how much over what period of time and if a change of a particular magnitude can actually be perceived by the taste buds.

To make a clay body for slip casting, particle distribution and suspension capability has to be considered. You typically cannot take a clay body that is formulated for forming processes like handbuilding or throwing characteristics and then just "make" it a slip casting body. Typically the composition of the slipcasting body gets modified to make it work for THAT particular forming method.

And to make a casting body slip, it MUST be deflocculated.... which means that a chemical that affects the ionic properties of the water is added so that it takes less water to make the suspension "fluid". This keeps the pieces from cracking in the molds as they dry due to excess shrinkage. It also decreases the water the mold needs to absorb to get the correct thickness of clay deposit. Slipcasting is a complicated process..... particularly at the commercial level.

I strongly doubt if a straight zisha clay that is used for hand construction would be used for the slipcasting body unaltered.

As to mold lines, there is also the forming process called press moulding. You take a plastic clay body and force it into a mould and then connect the various parts of the mold together to form the final object. This can be done by hand, or by hydraulic pressing methods. So mould lines do not necessarily mean slip casting.

I was told while in Yixing that the nature of the genesis of the pieces is directly related to the pricing, with a further link to the fame of the artist. It was CLEAR that the prices for the better works made out of the "real deal" clay are generally VERY high.

That old saying "you get what you pay for" holds true here. Just sayin'.

best,

.................john
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Re: What is the problem with slip cast yixing teapots?

Postby Tead Off » May 10th, '13, 04:41

+1 John!
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Re: What is the problem with slip cast yixing teapots?

Postby edkrueger » May 10th, '13, 13:48

Since I wrote that 2 years ago, I'm not quite sure what I meant. I was probably using terracotta to refer to the flaking.
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Re: What is the problem with slip cast yixing teapots?

Postby paul haigh » May 20th, '13, 10:36

In addition to what John said, that if there's a line down the middle, it may indicate slip casting or press molding, a slab-built (not molded) pot will tend to have seams at corners- not in the middle of a face. A dimple on the inside where the handle is joined is often an indication that it was slipcast with the handle attached (though absence of the dimple tells you nothing, as a handle could be added to a slipcast body or lid)
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