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Stoneware Thickness


Rich2020
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Hi

I want to attempt to make profile moulds for a jigger jolly as I'm a novice and don't have the skill to throw by hand. 

My question relates to the final thickness of stoneware? I'm trying to straddle the line between durability and aesthetics. Again I'm referring to final thickness recommendations out of the kiln. I will infer a 10 to 12% allowance for shrinkage.

I figure this is one of those how longs a piece of string sort of questions, but I guess I could get a roundabout answer from consensus or the average.

Thanks

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Hi Rich,

Good question! If there are any pottery stores/outlets/galleries nearby, you might spend some time checking out other potter works.

Durable <--> aesthetic, ok, perhaps strong <--> light; any road, trade offs, indeed.

I'm guessing many others also strive for thin and light, and once getting there, then move somewhat thicker for strength/durability and balance. I like the feel of foot ring; to me, it's worth the time, effort, and a smidge of weight for a) the ease of handling - a place for soapy fingers to catch, and b) it's easy to polish the part that touches one's table top. On the other end, I like the rim of a bowl to swell just enough that there's a perceptible recurve on the inside, again, for handling. I also like all rims to have enough "meat" that they can stand up to a bit of banging about, whilst not being uncomfortable to sip from; shape also matters for sipping - make a place to park that lower lip! The wall between foot ring and rim can go a bit thinner, and still be strong, imo ...also the base within the foot ring, where I'm looking to leave 4-5 mm (leather hard) on cups, mugs, and small to medium bowls. ...which brings up overall size, right? Bigger pieces, a bit thicker, for the curves are shallower, hence  more strength required? What sizes are you aiming for? What types of pieces?

So far, haven't directly answered your question, haha, yep, "it depends" - destructive testing can be a real good friend. Tap, tap, crash - not strong enough. Might as well get to it, for it (testing) will happen eventually anyway - oops, drop, bang, tap, etc., might as well accelerate that learning curve. There are so many variables! What clay? Clay fully vitrified/fired? What about handles? What target market(s) - corner diner? Eight dollar cup o' joe white tablecloth sit down?

Well fitting glaze can allow one to go a bit thinner and still be very strong, whilst a poor fitting glaze weakens (a lot).

Looking forward to reading what others may add here.

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You bring up some interesting points that I need to consider regarding the finer details. My goal isn't to make something that looks overly delicate, instead for daily use. I'm making cutting profiles for plates, bowls and mugs in various sizes. I think the biggest plate is going to be about ø30cm. 

image.png.15ee869a89b688899c584a6aba030a98.png

This is the style I'm going for, it looks about 3mm thick give or take to me. Clay I've not decided yet. I was hoping to leave the outside unglazed so wanted clay that turns blue grey and another clay that has a speckled tan colour when cooked at cone 6. I guess I need to go away and prototype between 3 and 5mm depending the size.

 

Thanks you both for taking the time to help out.

Edited by Rich2020
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13 minutes ago, Rich2020 said:

Oh, another topic I know next to nothing about. Well, I'm a glutton for punishment and enjoy a challenge. Are you aware of a particular substance needed in the mix for stability or less volatility?

It will have to fit your clay body with a pretty exact coefficient of expansion match in order to not push or pull on the clay as it cools.  Will take experimentation and durability testing.

Clay that is glazed inside and out will be a lot more durable than clay glazed on one surface, or unglazed entirely.  An analogy is think of a broom.  Now tape only one side of the bristles.  There's no change in strength of the bristles. But wrap the bristles all the way around with duct tape and now it's under compression, and much sturdier.  This is what glaze does, it squeezes the clay and strengthens it.

Edited by liambesaw
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Nice looking bowls Rich!

try tapping that edge with a butter knife handle. What's it take to chip away a flake?

They should be much stronger with glaze on both sides (as Liamb has pointed out); you might try glazing down the outside partway, so you're wrapping the edge at least - and easier to clean, nicer to sip from.

Lots to learn about glazes, suggest you start with a clear that fits your clay. One (of many) places to start, Tony Hansen's (incredible) online resource:

https://digitalfire.com/article/concentrate+on+one+good+glaze

https://digitalfire.com/4sight/education/what_is_the_glaze_dragon_38.html

https://digitalfire.com/4sight/education/trafficking_in_glaze_recipes_379.html

fwiw clay is tough on quality precision instruments; this (and flat rulers) is more than close enough (for me) in the clay studio

 

 

duhne.JPG

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It's interesting what you both say about the single side glaze being less durable. I noticed after reviewing a few examples of single sided glaze bowls they are indeed thicker, I guess it's a compensation. 

image.png.3e75d827ecd8508adee42a9664795170.png

 

Thanks guys, I think I have enough here start testing and looking for solutions.

 

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