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Tips on my slip casting journey


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Hi everyone, first post on this forum and i'm also new to ceramics. I've taken a really basic ceramics class long ago in college. I'm trying to slip cast a custom tray, but I'm having some trouble. I'm not sure if this is the best spot in the forum.

I just finished building the my kiln. It has a 220v, 3840 watts element, 3 inch IFB23 inner walls with 2 inch ceramic fiber board wall shell, and 3 inch floor, with an inner volume of 18 inches wide by 9 inches deep and 6 inches tall. Controller is a raspberry pi with 5 inch touch screen.

I modeled the part I'm trying to make in CAD, scaled it up by 13% and cut it out of polyurethane sign board foam. I then sealed the part with several coats of polyurethane and cast it in potters plaster #1 at a 1 lb 7 oz to 1 pint ratio. I used Slip 500L Laguna Stoneware. I waited about 1.5 hours before dumping the extra slip, however even after overnight, the body was still too floppy to take out the mold, I had to wait a few days before it was rigid enough to retain its shape. This induced the first cracks since I presume the plaster mold let it dry unevenly. I then did a long bisque to 04 and the temperature where the cone was located came out to be a little hotter.

I'm looking to have my part resemble a metal tray as much as possible so I elected to use  Amaco's Potter's Choice Palladium glaze. I put 5 normal coats on the part, however I still got green hue instead of silver. The firing schedule followed a 270*f/h to cone 7 as stated by the ceramic shop's info about the slip. (no watch cones for 7, they are still in the mail). On the top side of the part I got minimal pin holes, however on the bottom I got a bunch. The part also warped really badly and thus made it touch and fuse to the kiln shelf.

 

Questions for my next attempt.

What's the best way to cast a large flat part like my tray without deformation when popping it out of the plaster mold?

https://drive.google.com/file/d/10w5EYbK1kaTkT7kS-U0YZ6Uy1PZOnsrX/preview

https://drive.google.com/file/d/1s7fji9v0rl8LbT33RQCuoSLMYNM8T01_/preview

Would different slip be better for my part? I'm going to purchase mid fire slip this time so that I can properly fire to cone 6 fo for the glaze color (although, i've read people taking it above cone 6) Would a slip with heavy grog be more beneficial or porcelain slip? I was looking at using Slip, Dover White next.

 

The tray part was sitting on my shelf with no stilts when I bisqued, could this be the reason for the pinholes on the bottom of the tray and not the top? I will elevate the tray part when I do my next bisque.

https://drive.google.com/file/d/1ikJMgY7B9akmlAg_UMnZHplHYVfmxYZ-/preview

https://drive.google.com/file/d/1O66fOqutxrBch3DBs7DbZjTYnVrO2U6_/preview

https://drive.google.com/file/d/1v2WGRFreVbQYW-Pj3jNoaCM0iMtgb5E6/preview

 

What could have caused the tray part to warp so badly? I glaze fired the tray on 2 stilts, 

https://drive.google.com/file/d/1oy4QgOVwlTpWo2CFYCf4vR_WUrYl0w9f/preview

https://drive.google.com/file/d/1OHBcHJKz3yJmxwDDtJbC7Fcw6QJGBC0H/preview

 

Thank you in advance for any pointers!

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None of your links work, they're all linked to private files.

What deflocculant did you use in your slip?  It sounds to me like your slip has too much water in it.  

As far as the amaco palladium glaze, I don't think I've ever seen it come out silver like the test tile they show on the website.  Maybe if it's on porcelain.

It sounds like your kiln over fired the cone 7 firing by quite a bit if the tray drooped that badly.  Could be the cause of the bubbles and poor glaze result too.

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29 minutes ago, liambesaw said:

As far as the amaco palladium glaze, I don't think I've ever seen it come out silver like the test tile they show on the website.  Maybe if it's on porcelain.

Got it to work a few times, white stoneware and porcelain. Heavy application, very fickle about firing, especially pinholes. Too light of an application - More black than chrome.

6861C891-BF43-484F-BB88-E7915958B24C.jpeg

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16 hours ago, seesoe said:

I put 5 normal coats on the part, however I still got green hue instead of silver. The firing schedule followed a 270*f/h to cone 7...

I've never used Palladium - but have used a lot of other PC glazes, and most of them recommend 3 coats.  They are also all listed as Cone 5/6, so Cone 7 would be a little over-fired. 

Your Laguna 500L slip, on  the other hand, is listed as cone 10., so is 3 cones under-fired at cone 7.

Depending on how thick your 'normal coats' are, you're combining an over-fired, possibly too-thick glaze application with an under-fired clay...  all sorts of things could go wrong with that.

If you're going to use cone 5/6 glazes, I would recommend switching to a cone 6 slip - and firing in that range.  (Since you're using Laguna, maybe their "Dover NS4" would work.)

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17 hours ago, seesoe said:

The firing schedule followed a 270*f/h to cone 7 as stated by the ceramic shop's info about the slip.

Most kilns won’t do this rate at the top end , common is to use the 108 per hour temp (middle column in Orton chart for the desired cone) for about the last 200f (100c) of the firing so the controller can end at the desired cone.
So this explanation they have given you is a bit suspect.

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Thank you for the comments. I believe the links should be working now. Bill your results look great, I’d be happy with something like that.

 

6 hours ago, liambesaw said:

None of your links work, they're all linked to private files.

What deflocculant did you use in your slip?  It sounds to me like your slip has too much water in it.  

As far as the amaco palladium glaze, I don't think I've ever seen it come out silver like the test tile they show on the website.  Maybe if it's on porcelain.

It sounds like your kiln over fired the cone 7 firing by quite a bit if the tray drooped that badly.  Could be the cause of the bubbles and poor glaze result too.

I never added anything to the slip, it came pre mixed.
 

28 minutes ago, Rockhopper said:

I've never used Palladium - but have used a lot of other PC glazes, and most of them recommend 3 coats.  They are also all listed as Cone 5/6, so Cone 7 would be a little over-fired. 

Your Laguna 500L slip, on  the other hand, is listed as cone 10., so is 3 cones under-fired at cone 7.

Depending on how thick your 'normal coats' are, you're combining an over-fired, possibly too-thick glaze application with an under-fired clay...  all sorts of things could go wrong with that.

If you're going to use cone 5/6 glazes, I would recommend switching to a cone 6 slip - and firing in that range.  (Since you're using Laguna, maybe their "Dover NS4" would work.)

ya I think I really need to triple check my firing schedule when my cones come in. I also did read somewhere an Amaco engineer saying porcelains give better results on palladium. Would you suggest porcelain over Dover NS4? Since This is going to be a functional piece, My original idea was to use cone 10 stoneware to get the strongest parts. Through my journey so far from from reading I learned that a properly fired piece at cone 6 can be just about as good. And that if you aren’t doing anything fancy with glazes, then an oxidation electric kiln at cone 10 is pointless.

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10 minutes ago, Bill Kielb said:

Most kilns won’t do this rate at the top end , common is to use the 108 per hour temp (middle column in Orton chart for the desired cone) for about the last 200f (100c) of the firing so the controller can end at the desired cone.
So this explanation they have given you is a bit suspect.

Bill this would make sense, as to get “more resolution” in the important top end of the firing. I will recalculate my firing schedule before my next cone test.

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32 minutes ago, seesoe said:

Thank you for the comments. I believe the links should be working now. Bill your results look great, I’d be happy with something like that.

 

I never added anything to the slip, it came pre mixed.
 

ya I think I really need to triple check my firing schedule when my cones come in. I also did read somewhere an Amaco engineer saying porcelains give better results on palladium. Would you suggest porcelain over Dover NS4? Since This is going to be a functional piece, My original idea was to use cone 10 stoneware to get the strongest parts. Through my journey so far from from reading I learned that a properly fired piece at cone 6 can be just about as good. And that if you aren’t doing anything fancy with glazes, then an oxidation electric kiln at cone 10 is pointless.

Palladium is not food safe, so hopefully by functional you don't mean the traditional meaning

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22 minutes ago, seesoe said:

a properly fired piece at cone 6 can be just about as good

A ^6 body fully matured will be better for almost any purpose than a ^10 body that's only fired to ^7.

 

25 minutes ago, seesoe said:

This is going to be a functional piece,

What sort of "function" ?  Palladium is clearly labeled "Not Food Safe" - which rules out using it on any surface that might come in contact with food or beverage.

 

27 minutes ago, seesoe said:

Would you suggest porcelain over Dover NS4?

My only experience with slip-casting has been low-fire (^04) Christmas ornaments, so don't know about that - was just suggesting the NS4 as it is also a Laguna slip, that looks to be a similar color to the 500L, but at ^6 to match the glaze you're using. 

 

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After plowing thru all your goggle drive photos

Looks like you have what is called a press mold-no need to use slip.

use a slab of cone 6 clay-rolled out and pressed into your mold with no top.Use a body with some tooth so it can take getting pressed into corners and will not warp during firing.

Start with a dry mold. If the piece is cracked after bisque or warped toss it and make a few more.Make them thick enough not to warp.

Do not glaze the bottom of tray -it must sit flat unless its a low fire deal

 

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3 hours ago, seesoe said:

Bill this would make sense, as to get “more resolution” in the important top end of the firing. I will recalculate my firing schedule before my next cone test.

I would like to take credit but if you read the Orton chart it just says to use the cones this way. Cones are made of glaze, grind up a cone six cone, fire it to cone ten, it’s a nice glaze. In about the last 200f or 100c of the  firing is where meaningful irreversible heatwork happens, it’s more of a flux thing.  
I have seen plenty of those pinholes with that glaze and after using it a bunch believe it is a fired surface tension thing. You may want to google digital fire for a drop and hold schedule to clear the pinholes. My experience, this glaze is fickle and likely benefits from it.

To add, after your google drive got unlocked, I think @Mark C. is spot on, cone 6 clay, make life easier.

Edited by Bill Kielb
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On 8/17/2020 at 8:30 AM, Sorcery said:

You mean....like....a lid?

Sorce

No, like an ashtray.

 

On 8/16/2020 at 8:54 PM, Bill Kielb said:

I would like to take credit but if you read the Orton chart it just says to use the cones this way. Cones are made of glaze, grind up a cone six cone, fire it to cone ten, it’s a nice glaze. In about the last 200f or 100c of the  firing is where meaningful irreversible heatwork happens, it’s more of a flux thing.  
I have seen plenty of those pinholes with that glaze and after using it a bunch believe it is a fired surface tension thing. You may want to google digital fire for a drop and hold schedule to clear the pinholes. My experience, this glaze is fickle and likely benefits from it.

To add, after your google drive got unlocked, I think @Mark C. is spot on, cone 6 clay, make life easier.

Bill, I looked up drop and soak, and that looks like it will do the trick, fingers crossed! I'm calculating a new firing profile now for my controller. I will be using the middle column of 108 f/h starting at 2232 F minus 180 F, and then apply drop and soak. I found this c6 drop and soak as well that I will try out. My 5, 6, 7 cones arrived, and my Porcelain Antique White NS124 slip, and Dover White NS4 slip are on the way. I decided to experiment both c6 stoneware and c6 porcelain.

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  • 3 weeks later...

Drop and soak seemed to help, although I didn't glaze the underside which is were most the blistering was occuring. This newly fired piece didn't have any blisters so I will continue to use this technique on the PC-04 Palladium since it is a runny glaze.

I followed orton's medium chart column, ramped at 108 d/h starting 180 degrees below cone 6, held for 10 minutes, allowed 5 minutes to drop 150 degrees, held there for 30 minutes,  cooled to 1400 degrees at 150 d/h and then free fall.

Here are the 04 bisque cones on the left and 6 glaze cones on the right (guide, target, guard). I need to find out how much to drop the glaze temperature so it won't over fire that much. Small note on cone placement, I don't have much space so the cones were places at the edge of the shelf and not 1 inch into the shelf. Also the shelf is about 3/4-1" away from the wall all the way around.

https://drive.google.com/file/d/1jb3CVQ44PX2XLduj7SUJZZnWDkqnBVM6/view?usp=sharing

 

I applied kiln wash to my shelves this time around and I put the tray flat on the shelves with no support. Kiln wash seemed to work its magic perfectly. My biggest 2 issues now is the color and slumping. In the 4th picture you can see that the middle slumped all the way until it made contact with the shelf, but it is supposed to be about 5.5 mm away from the bottom. You can see on the left side how it is away from the bottom like it should be and it never sagged iand touched the shelf. The glaze is almost to color, it lusters but still lacking. I applied 3 coats, but it seems like they might of been too light.

https://drive.google.com/file/d/11zWPSJcP1G5Z-u0LNZSHCEGoeIyMmcmj/view?usp=sharing

https://drive.google.com/file/d/1MtcyU6lcSug0jLfLc6Kzt3o3U0KnxGvE/view?usp=sharing

https://drive.google.com/file/d/1jJiqw6Ks56OctQdhCd7NbPY3Coo6pq_z/view?usp=sharing

https://drive.google.com/file/d/1qJykqhLpcvwzxHsURqrI-XsMJj42jRS4/view?usp=sharing

 

How can I prevent the sagging in the middle? is possible to use a prop like a slab to support it from under? If so would it be a bisqueware or greenware slab? (to be able to calculate the proper height needed)

For the ones that have used this PC-04 Palladium glaze, does it seem like my 3 coats were too light or could my results be a firing issue?

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1 hour ago, seesoe said:

For the ones that have used this PC-04 Palladium glaze, does it seem like my 3 coats were too light or could my results be a firing issue?

Looks good,  some of our Ikebana vessels required propping. Especially long sweeping forms made from very white porcelain that would tend to slump But we were always able to design so a kiln shelf post could be used to prop. When throwing large porcelain lids I was always able to increase the crown height enough so the clay would not slump in the firing using the throw a right side up lid approach.  They do start to get tall and ugly though at some point.


Other ideas that come to mind are increase the crown in some of the low height bends and potentially add a local foot or rib  to the bottom  or prop, to free spans that are too large to span. You certainly can make your own from clay and alumina wax them to prop underneath as needed.

And yes my experience with Palladium is, too thin and it doesn’t work, too thick can be a bit ugly as well but the common error is too thin. Drop and hold seems to have helped  a bunch, cone five fifteen to get your cone six  heatwork and your drop and hold might help the slumping and the theoretical fired surface tension bubbles thing.

87519DA1-4C45-49BC-95D2-1D9EBCBE9256.jpeg

Edited by Bill Kielb
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2 hours ago, Bill Kielb said:

Looks good,  some of our Ikebana vessels required propping. Especially long sweeping forms made from very white porcelain that would tend to slump But we were always able to design so a kiln shelf post could be used to prop. When throwing large porcelain lids I was always able to increase the crown height enough so the clay would not slump in the firing using the throw a right side up lid approach.  They do start to get tall and ugly though at some point.

 

the black work on that piece looks really nice!

 

2 hours ago, Bill Kielb said:

And yes my experience with Palladium is, too thin and it doesn’t work, too thick can be a bit ugly as well but the common error is too thin. Drop and hold seems to have helped  a bunch, cone five fifteen to get your cone six  heatwork and your drop and hold might help the slumping and the theoretical fired surface tension bubbles thing.

I will try 4 coats on the next piece. What do you mean by cone five fifteen to get cone 6?

 

2 hours ago, Bill Kielb said:

Other ideas that come to mind are increase the crown in some of the low height bends and potentially add a local foot or rib  to the bottom  or prop, to free spans that are too large to span. You certainly can make your own from clay and alumina wax them to prop underneath as needed.

 

I was thinking to make a bisqueware clay slab prop with kiln wash applied to it.  You think would that work?

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2 hours ago, seesoe said:

What do you mean by cone five fifteen to get cone 6?

When folks want cone six but have temp sensitive glaze or clay they will fire one cone lower with a  soak. So generally cone 5 with a fifteen minute hold will actually be cone six. The hold is generally fifteen to twenty minutes to get the cone six to fall By heatwork without reaching cone six top temp. It’s not linear so firing one cone is doable but firing two or three cones with longer soaks often does not work well.
 

2 hours ago, seesoe said:

I was thinking to make a bisqueware clay slab prop with kiln wash applied to it.  You think would that work?

Yes I think that could work especially with some room for trial and error. I am an alumina guy though but if kiln wash is working....

 

2 hours ago, seesoe said:

the black work on that piece looks really nice!

My wife is a real artist, all freehand brushwork. She just sits down and creates it underglaze and brush in hand. She has got real skills!

Edited by Bill Kielb
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