Rich2020 Posted February 4, 2020 Report Share Posted February 4, 2020 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 Link to comment Share on other sites More sharing options...
Hulk Posted February 4, 2020 Report Share Posted February 4, 2020 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. Link to comment Share on other sites More sharing options...
neilestrick Posted February 4, 2020 Report Share Posted February 4, 2020 It depends......Are you going for something light and delicate, or thicker country pottery feel? Around 3/32" thick would probably be a good middle ground. Link to comment Share on other sites More sharing options...
Rich2020 Posted February 4, 2020 Author Report Share Posted February 4, 2020 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. 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. Link to comment Share on other sites More sharing options...
liambesaw Posted February 4, 2020 Report Share Posted February 4, 2020 You might run into troubles only glazing the inside, especially with plates and bowls. It can pull them out of round and cause tension that can get dangerous in combination with hot foods. You'll have to formulate a special glaze if you do that. Link to comment Share on other sites More sharing options...
Rich2020 Posted February 4, 2020 Author Report Share Posted February 4, 2020 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? Link to comment Share on other sites More sharing options...
liambesaw Posted February 4, 2020 Report Share Posted February 4, 2020 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. Link to comment Share on other sites More sharing options...
neilestrick Posted February 4, 2020 Report Share Posted February 4, 2020 Go to Target or some other store that sells cheap dishes and buy one that has the weight you want in your pieces, and measure the thickness with a digital caliper. Link to comment Share on other sites More sharing options...
Hulk Posted February 5, 2020 Report Share Posted February 5, 2020 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 Link to comment Share on other sites More sharing options...
Rich2020 Posted February 6, 2020 Author Report Share Posted February 6, 2020 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. Thanks guys, I think I have enough here start testing and looking for solutions. Link to comment Share on other sites More sharing options...
liambesaw Posted February 6, 2020 Report Share Posted February 6, 2020 Awesome! Be sure to let us know how things... turn out Link to comment Share on other sites More sharing options...
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