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Tiki Central Forums Creating Tiki Other Crafts Plaster Mold Making & Some Ceramics
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Plaster Mold Making & Some Ceramics
Robin
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Joined: Jul 01, 2007
Posts: 402
From: where the road and the sky collide
Posted: 2008-04-28 08:40 am   Permalink

Thanks you guys, this is great! I've tended to stay away from plaster...I'm the kind of worker who gets stuff everywhere...floor, walls, hair, eyes, mouth,etc....working in clay made that problematic. I didn't notice to much mess around in your photos....maybe there's hope. Seriously though priceless tips and photos...thanks so much for doing this...it's a great reference.

 
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MadDogMike
Grand Member (6 years)  

Joined: Mar 30, 2008
Posts: 7318
From: The Anvil of the Sun
Posted: 2008-04-29 6:09 pm   Permalink

OK Bowana & Babalu, I'm heading back to SD Thursday to pick up some slip from Freeform. I made a model out of wax, somewhat crude but it will work for a first try. I made a 3 piece mold, also somewhat crude. I didn't do a very good job on the parting line, I'm afraid I'll have lots of fettling to do (is that the right word). If this mold doesn't work out, I'll make a new one and be more careful this time.
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MadDogMike
Grand Member (6 years)  

Joined: Mar 30, 2008
Posts: 7318
From: The Anvil of the Sun
Posted: 2008-04-29 6:38 pm   Permalink

Hey, what should I get for slip? (Brand? Color? Cone?)

 
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Bowana
Grand Member (6 years)  

Joined: Nov 10, 2006
Posts: 1168
From: La Mesa, CA
Posted: 2008-04-30 07:17 am   Permalink

MadDog-
All the slip I've ever bought came in plastic milk containers with no brand. Get a low fire slip like cone 04 or 06. White slip is best because it allows for the glaze colors to be more accurate.

Good separation lines are very important. Take as much time as you need making them. You'll learn as you make more.

Bowana
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GROG
Grand Member (first year)  

Joined: Jun 21, 2006
Posts: 6882
From: Tujunga
Posted: 2008-04-30 08:18 am   Permalink

GROG not remember you guys mentioning "shrinkage". Shouldn't your sculpt be a little larger than what you want the final ceramic size to be?

If GROG remember GROG' ceramic-making correctly, after the mold is made, the slip is poured into the mold, and once hardened enough it is removed from the mold and is called greenware. As it dries it shrinks. Then, when it is fired it shrinks some more if GROG remember correctly. Thus, your finished ceramic will be smaller than your original sculpt.

About what percentage of shrinkage can you expect?


 
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GROG
Grand Member (first year)  

Joined: Jun 21, 2006
Posts: 6882
From: Tujunga
Posted: 2008-04-30 08:27 am   Permalink

An example of shrinkage. The greenware on the left is darker and taller because it is fresh out-of-the-mold, and hasn't dried much. The greenware to the right is lighter and shorter because it has shrunken as it dried.



[ This Message was edited by: GROG 2008-04-30 08:31 ]


 
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Babalu
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Joined: Nov 19, 2006
Posts: 2505
From: Lemon Grove
Posted: 2008-04-30 11:02 am   Permalink

Grog is sooo right! This should have been discussed in the beginning. As you are sculpting your master you will need to take into account that clay shrinks as it dries...it also shrinks during the firing process. A typical shrinkage rate (depending on your clay body) is between 4% and 10% as the green ware (unfired clay) dries. Clay can also shrink as much as 8% in the firing of the clay. Some clays have more "grog" (no pun) added to them which will reduce the shrinkage rate during firing. Grog is is finely ground bisqued clay that has been added to the clay. This added grog not only reduces shrinkage, it also makes for a more sculptural clay, and helps with the thermal shock of the firing.

Most of the mugs that you guys like are made with low fire (cone 04) slip. This type clay shrinks a bit, but one can also get some really nice store brought colors with the low fired glazes (cone 06) that are available for this type of cone 04 clay.

I would venture to say that this mug of mine shrinks a total of approximately 12-14% during the drying and firing.

I know Bowana still has some "how to" mold making photos to post yet. After he has done that I will dive a little into glazing and firing for you.

Thanks Grog for catching the shrinkage thing...


 
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MadDogMike
Grand Member (6 years)  

Joined: Mar 30, 2008
Posts: 7318
From: The Anvil of the Sun
Posted: 2008-05-01 7:52 pm   Permalink

Back to the drawing board! Well I got some slip today (Laguna S695 white stoneware, cone 5) and cast my first mug. Everything went well except the bottom of the mug tore when I took it out of the mold (Other than that Mrs. Lincoln, how was the show?) I made the rim and concave bottom, but didn't heed the advice to make a separate piece of the mold for the bottom. Now it seems there's no way to remove the mug without tearing it.
That's OK, I needed to make a new mold anyway. My separation lines were a little rough but they cleaned up nicely with a loop tool. I'm not discouraged and I have lots of plaster and slip!
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Babalu
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Joined: Nov 19, 2006
Posts: 2505
From: Lemon Grove
Posted: 2008-05-01 9:46 pm   Permalink

Hey Mad Dog,

That a way to go! Don't get discouraged. Keep after it. It will happen.

I notice that you mentioned that you brought a Cone 5 slip. This slip fires quite a bit hotter than the cone 04 slip that Sir B and I are using...Cone 04 = 1940 degrees Fahrenheit...Cone 5 = 2185 degrees Fahrenheit. Just make sure when you buy glazes that you have them show you to the glazes that are compatible to your slip. These days they make quite a few colors for cone 5 - cone 6. Do you have your own kiln?


 
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MadDogMike
Grand Member (6 years)  

Joined: Mar 30, 2008
Posts: 7318
From: The Anvil of the Sun
Posted: 2008-05-02 07:28 am   Permalink

Freeform had lots of cone 5 glazes. Do you know of anyone in SD area that will fire pieces for a small fee? There is a local woman here who will do a kiln-full for $40, but that's only ecomonical if you fill the kiln. Freeform had a small used 110v kiln for $150 and there's a medium-sized Cress LT-4K 220v that I know of avail for $200.
I would like to fire a few pieces before I buy a kiln, see if I have even a smidgen of talent. So far, I'm only about $20 into this deal and can walk away if I find out I suck!
Babalu, thanks for your time and advice!

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Babalu
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Joined: Nov 19, 2006
Posts: 2505
From: Lemon Grove
Posted: 2008-05-02 10:14 am   Permalink

Hey Mad Dog,

I would be happy to toss a few of your mugs into one of my firings if you like, however, everything I'm firing right now is low fire. If you bring your new mold over, I have quite a bit of the cone 04 slip you can try in it.

It sounds like you didn't buy to much of that cone 5 slip? That's probably a good thing.


 
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Tiki Kaimuki
Grand Member (4 years)  

Joined: Sep 25, 2006
Posts: 821
From: OAKLAND, baby
Posted: 2008-05-02 10:38 am   Permalink

I haven't had much luck with the Laguna Cone 5 white stoneware. I'm switching to morrocan sand and will probably add a bit of grog for more strength. Babalu, do you mix your own slip or do you buy premixed?
This is a very valuable thread, by the way. Mahalo for starting it!


 
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Cammo
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Joined: May 18, 2006
Posts: 1952
From: San Diego
Posted: 2008-05-02 11:03 am   Permalink

I think Babalu should come up with a small per-mug fee for firing, we figured it isn't too expensive, but there is a cost involved in electricity at his end.

Shrinkage -

When I made my Oki Doki mug, I made it extra BIG because I thought it would shrink like crazy, both in the drying and in the first firing. But it HARDLY SHRINKS AT ALL! I ended up with a giant 24-oz mug that was WAY bigger than I thought possible. It shrinks, but our final glazed mug measured to 94% of the original. We're using the Freeform white slip; Babalu has the exact cone info.

So don't sweat the shrink.

And - go crazy with glazes. Try everything. Lots of transparent colors. Try stuff on top of stuff, and take notes. (Number your mugs to help you do this.) We've been experimenting for a long time and have barely started yet. If you layer two glazes they form amazing colors unlike either of the glazes themselves, and burst out in cool looking hues...

[ This Message was edited by: Cammo 2008-05-02 11:18 ]


 
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MadDogMike
Grand Member (6 years)  

Joined: Mar 30, 2008
Posts: 7318
From: The Anvil of the Sun
Posted: 2008-05-02 12:33 pm   Permalink

Babalu, thanks for the generous offer, but you have to promise not to make fun of my lack of sculpting ability
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Bowana
Grand Member (6 years)  

Joined: Nov 10, 2006
Posts: 1168
From: La Mesa, CA
Posted: 2008-05-02 8:56 pm   Permalink

GROG pretty smart for caveman. Bowana think GROG not Neanderthal any more. GROG move up one rung on evolutionary ladder to Cro-Magnon Man with knowledge of ceramics.

Sorry to hear about your mold, MadDog. Try it again! You'll just keep getting better.




Here is the mold with the third piece already having been poured. The separation line is clearly visible. The orange worm looking thing in the middle of it is a piece of oil clay I stuck onto the separation line before pouring the third piece. This little trick will leave a small dent in the plaster part when the clay is pulled off that will serve as an aid in getting the mold pieces apart.




At this stage the wooden form has been removed. The fourth and final piece (which was the round bottom piece) regrettably was not photographed while being made.

I use these plastic wedges from bought at Free Form to open the mold. The wedge is inserted into the shallow depression left by the clay worm in the previous picture. This gets the wedge started on the opening process much easier than if it were to be driven straight into the plaster. It's like giving it a bit of a head start.




Gently tap the wedges with a mallet and work your way around the mold using several wedges. Don't wail on the mallet though. The plaster is hard, but can still be broken if handled rough. This view shows the top of the mold with opening for pouring the slip (or Barbotina for our Spanish speaking friends)




One of the most rewarding steps in the entire process is seeing the space widen between two mold parts. It means that they did not stick together!





Here is the finished four part mold of Babs' Man 'O War mug showing the previously mentioned bottom piece.





This is Cammo's Oki Doki mug mold. The design on this one was a bit more simple so it required two side halves instead of three.

Take the mic, Babs...



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