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kraythe

Glazing to the base without freezing to shelf?

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I am just a self taught hobbyist but I have been making some mugs. My handles still aren’t yeh best but my latest attempt is attached (partially dried). It has a cut ring above the rim for decoration and I wanted to glaze all the way to the base of the pot but I am worried about the pot sticking to the shelf. Any suggestions for preventing this but still glaze all the way to the base? Thanks.

665DBAD0-0518-498D-B1D5-ED15B635AEBA.jpeg

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Take some of the same clay and make some circles just slightly smaller than the base diameter of the mugs and about 1/4" thick and dry them between boards so they stay flat. Bisque fire them then set mugs on the bisqued circles of clay. If your glaze is fairly stiff this should work, if it's runny then you're going to have to grind off glaze drips. If you cut more of an undercut at the base of the mug you don't really see much raw clay at all.

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11 hours ago, Min said:

Take some of the same clay and make some circles just slightly smaller than the base diameter of the mugs and about 1/4" thick and dry them between boards so they stay flat. Bisque fire them then set mugs on the bisqued circles of clay. If your glaze is fairly stiff this should work, if it's runny then you're going to have to grind off glaze drips. If you cut more of an undercut at the base of the mug you don't really see much raw clay at all.

I don't follow what you mean about the undercut. The very base of the mug is visible in this closeup. 

As for your suggestion, a plinth! I feel silly now that I didn't think of that. 

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6 minutes ago, kraythe said:

I don't follow what you mean about the undercut. The very base of the mug is visible in this closeup. 

As for your suggestion, a plinth! I feel silly now that I didn't think of that. 

Undercut, like a sharp inward angle/ bevel.  This can be done when finishing throwing, (I usually opt for a wood knife for this), or when trimming a foot.  In either case,  this angled/ beveled portion is partially hidden by the shadow of the rest of the form.   In some case, I underglaze my feet black, which hides the bare clay, and adds to floating appearance that the trimmed foot helps create.

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What cone are you firing to? if I'm doing low fire glazing, many times I will glaze the entire piece and set it in the kiln on a small 3 pin stand which you can get at any ceramic supplier. (I've even got to making my own...) The pins leave tiny marks on the bottom of the piece which are pretty insignificant. With High-fire, the plinths work well, but I think the undercut would be better. Here's an example of a ^6 firing where Amaco's "Paladium" was used under Amaco's Blue Rutile. The drips are the palladium which ran like a track star. At first I was going to try to grind them off, but then I thought they actually looked pretty cool and would also act as a reminder of what NOT to do.

Good luck with your future pieces!

JohnnyK

5a9035ef57c73_DrippyMug.jpg.bc33334cb46ac83fe49ab4d17e6b6499.jpg

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I am firing to cone 10 with those mugs so none of the pin stands will work, I can use an old cone holder or, what I will probably do, just fire a small circular plinth stand. 

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I often fire pieces in a cone 10 reduction kiln on seashells filled with wadding when the support point is in a glazed area. 
The shell does leave a slight mark where it makes contact, but knowing that will happen, I plan for the mark being a part of the overall design.  The wadding inside the seashell to provide a supporting the structure since the shell itself is decomposed into burnt lime, a.k.a. calcium oxide.  the wadding inside the shell can be scraps of clay that will withstand the firing temperature.  The lime will absorb moisture after the firing and will wash away after a few minutes of soaking in water.  Some touch up of the glaze might be needed to remove sharp edges.
LT

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When you trim your pots, use the side of your needle tool to make 2 or 3 concentric rings just above the foot. They will help to slow down glaze runs. If you're just doing a single glaze, and it doesn't run much, you can get within 1/8" of the bottom and not have to worry. Like others have said, cut a bevel at the foot to give some space between the glaze and the shelf. The bevel also looks better than a sharp corner, and is less likely to scratch a table top.

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On 2/24/2018 at 6:10 PM, neilestrick said:

When you trim your pots, use the side of your needle tool to make 2 or 3 concentric rings just above the foot. They will help to slow down glaze runs.

Basically, they are the equivalent of the spike strips the Police use to end high speed chases...

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It's common above earthenware temperatures to leave the foot ring bare, and just stop the glaze 2 mm (1/8") or so from the bottom of the pot, or more if the glaze is known to be runny. In most instances, it isn't practical (or particularly aesthetically pleasing) to glaze the entire foot of the pot. It's a more practical approach to consider the design of the foot carefully so that it looks good while unglazed, and doesn't scratch the surfaces it's set on. 

You *can* use wadding (simple recipe 50/50 kaolin and alumina hydrate) to prop your pots off the shelf with, but the wads themselves will stick into the glaze, and you will have to grind them off, and smooth the foot.  Lots more work. 

Edited by Callie Beller Diesel
Added.

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4 hours ago, Callie Beller Diesel said:

It's common above earthenware temperatures to leave the foot ring bare, and just stop the glaze 2 mm (1/8") or so from the bottom of the pot, or more if the glaze is known to be runny. In most instances, it isn't practical (or particularly aesthetically pleasing) to glaze the entire foot of the pot. It's a more practical approach to consider the design of the foot carefully so that it looks good while unglazed, and doesn't scratch the surfaces it's set on. 

You *can* use wadding (simple recipe 50/50 kaolin and alumina hydrate) to prop your pots off the shelf with, but the wads themselves will stick into the glaze, and you will have to grind them off, and smooth the foot.  Lots more work. 

You misunderstand, I dont want to glaze the bottom of the foot, just down TO the bottom. The part sitting on the kiln shelf would be unglazed. 

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4 hours ago, oldlady said:

you must have a reason for wanting to do this, could you explain why you would want to glaze the entire foot?   

I just don't want a visible ring of raw clay unless you turn the pot over and look at the bottom of the foot. That's all. 

Edited by kraythe

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In that case, it's a matter of now learning your glazes, and how much they move, or don't move when they're in the kiln. It's part of the process, and why one of the most common (and aggravating!) answers is to test it and see, because it depends on the glazes you're using, how thick they are, how you combine them with other glazes, etc etc etc.

I'd leave an area bare 1/8" up from the bottom, which is really not a lot. You can do it with practice with wax resist. If you're concerned about the glaze running, put a clay waster or a cookie underneath the piece to protect the kiln shelf until you get the hang of things.  You could even make the waster out of the wadding recipe I mentioned earlier, but if you don't have the materials handy to make it, just use clay. 

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If you want to glaze all the way down to the foot then you just need to adjust your glaze so that it doesn't move at all. That isn't that hard to do, but it will change the look of the glaze slightly. You could reduce the amount of flux in the glaze and watch it stiffen up and stay put. If this isn't something you want to do then your basically going to have to do things like others have recommended. Add ways for the glaze to meet resistance. People do all sorts of things. I leave little bevels near the bottom of my work. Other potters have their work flare out near the bottom, etc etc.

Edited by Joseph F

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Yeah,  the reason that people don't glaze all the way down is because grinding sucks, and shelves are expensive.   If you are doing any kind of volume, not grinding pots or shelves is a huge lift to productivity.  A lot of folks I know will wax the bottom and then glaze, but wax and I do not have a good working relationship.  I have started to put my pieces down on a good stiff damp sponge and give it a twist.   you wind up with just the smallest unglazed area at the bottom and it's a smoother transition from the clay to the glaze as it kind of feathers in.  

But definitely, design the foot to get the look that you want.   I like a good foot so that I can dip a piece by holding the foot.  Then I do the sponge and get a nice clean foot.  

The other thing is to get used to trying things.  Make samples of pieces and try the approaches.  Take good notes and then go with what feels most comfortable, attractive, and productive.   Make a bunch of small cups and try different types of feet and finishes.   It's also good practice on throwing multiples.  

Test everything and make good notes.  One of the guys I know literally times his dips based on the specific gravity of the glaze measured by hydrometer.     

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