Jump to content
Sign in to follow this  
Chris Campbell

What Is The Most Incorrect "rule" You Ever Heard For Pottery?

Recommended Posts

OffCenter    82

 

The most prevalent one is that ... clay fired to higher cones is stronger than clay fired to lower cones.

 

Jim

 

Does the higher cone do a better vitrification? Any other benefits of the higher cone at all?

 

 

Absolutely not and no. Firing to the maturity point of the clay and the composition of the clay determine the strength of clay. I really don't want to get into it again because it has been debated here to exhaustion, but Pete Pinnell published the results of the testing he and his university ceramics classes did a few years ago. The test used to determine the fired strength of clay is called a MOR (Modulus of Rupture) test. After a lot of testing the results were what they were expecting in that some mid-range clays were stronger than some higher fired clays and vice versa. What surprised them was that one of the earthenware clays fired to cone 03 or 04 or something like that was the strongest clay tested. Pinnell's tests weren't the only MOR test to prove that but was the most recent. You don't have to do MOR test to see the obvious; you just have to use a lot of different clays. For example, there is no doubt in my mind that my cone 6 porcelain is stronger than my cone 13 woodfire clay and just as strong as my cone 10 porcelain.

 

Jim

Share this post


Link to post
Share on other sites
Benzine    610

"The test used to determine the fired strength of clay is called a MOR (Modulus of Rupture) test."

 

It's also the name of my upcoming concept album.

Share this post


Link to post
Share on other sites
OffCenter    82

"The test used to determine the fired strength of clay is called a MOR (Modulus of Rupture) test."

 

It's also the name of my upcoming concept album.

 

Figures! Are you still using a sofa to sit on when you throw?

Share this post


Link to post
Share on other sites
Benzine    610

 

"The test used to determine the fired strength of clay is called a MOR (Modulus of Rupture) test."

 

It's also the name of my upcoming concept album.

 

Figures! Are you still using a sofa to sit on when you throw?

 

Naw, I've moved on to a padded desk chair.....I'm serious.

Share this post


Link to post
Share on other sites
mregecko    18

1. Never trim the inside of a bowl. I don't do this often but recently tried it after watching the video of the potter trimming the large, porcelain bowl. It works.

 

2. Never throw down. If a cylinder gets off-kilter or torqued, throwing down toward the wheel will often correct the problem.

 

#2 is my favorite! I just found this out a few months ago, when I was throwing some thin spouts for ring holders. Throwing down helped even out when I had weird torsion!

Share this post


Link to post
Share on other sites
oldlady    1,323

you cannot EVER put greenware and bisque in the same glaze firing.

Share this post


Link to post
Share on other sites
ayjay    119

 

My first pottery teacher was just a treasure trove of false information and iron clad rules that were her opinion only and nowhere close to the truth. She proudly claimed to be totally self taught ... or not.

 

 

I'm not very good at listening to rules, so can't claim to remember any bunkum ones - but...........

 

I often work with another carpenter who claims to be self-taught.................... I  usually retort that I don't think he was paying enough attention.

Share this post


Link to post
Share on other sites
Mark C.    1,807

I knew that splash pans would draw a response

Hey for some reason my pit fired dinnerware is not holding up ?? Any ideas why?I know its vitrified

 

 

Real Myths I have heard

Pots need to breath  leave  lots of space between them (when loading into a kiln)

Cones go bad (only when they get wet)

Pottery cannot be thrown and fired same day-(drop by some sunny day and see how this is done)

Mark

Share this post


Link to post
Share on other sites
OffCenter    82

I knew that splash pans would draw a response

Hey for some reason my pit fired dinnerware is not holding up ?? Any ideas why?I know its vitrified

 

 

Real Myths I have heard

Pots need to breath (when loading into a kiln)

Cones go bad (only when they get wet)

Pottery cannot be thrown and fired same day-(drop by some sunny day and see how this is done)

Mark

 

The reason your pit fired dinnerware is not holding up is because it is not vitrified (and because it doesn't exist). Drop by on a cloudy day and see how I can throw a pot and fire it the same day. (Pretend I inserted a smilely face here.)

 

Jim

Share this post


Link to post
Share on other sites
Claypple    29

 

 

The most prevalent one is that ... clay fired to higher cones is stronger than clay fired to lower cones.

 

Jim

 

Does the higher cone do a better vitrification? Any other benefits of the higher cone at all?

 

 

Absolutely not and no. Firing to the maturity point of the clay and the composition of the clay determine the strength of clay. I really don't want to get into it again because it has been debated here to exhaustion, but Pete Pinnell published the results of the testing he and his university ceramics classes did a few years ago. The test used to determine the fired strength of clay is called a MOR (Modulus of Rupture) test. After a lot of testing the results were what they were expecting in that some mid-range clays were stronger than some higher fired clays and vice versa. What surprised them was that one of the earthenware clays fired to cone 03 or 04 or something like that was the strongest clay tested. Pinnell's tests weren't the only MOR test to prove that but was the most recent. You don't have to do MOR test to see the obvious; you just have to use a lot of different clays. For example, there is no doubt in my mind that my cone 6 porcelain is stronger than my cone 13 woodfire clay and just as strong as my cone 10 porcelain.

 

Jim

 

Thanx Jim! I thought at first that you were saying that you do not have to fire clay up to the maturity temperature.

Share this post


Link to post
Share on other sites
Pugaboo    438

Okay so the rule about air bubbles isn't true? I live in terror of air bubbles exploding my ware! In fact I was at the group studio the other day and someone else's piece was laying on the kiln room table in what was shards basically. I asked what happened, thinking maybe the clay had not been dry enough to bisque since it was quite a thick piece. I was told that no most likely they had used reclaimed clay and not properly wedged it so it had air bubbles and that's why it exploded.

 

So ARE air bubbles a major issue? Or am I wasting my time wedging my clay until my arms are numb? I should also state in full honestly that I am also terrified of firing possibly damp pieces so often keep them for weeks before firing just to be sure they are dry. The "it will feel cool if damp test" doesn't work when it's been raining for so long I am considering purchasing an ark.

 

Can you tell by looking at an exploded piece what caused it?

 

Love this topic by the way I am learning a lot.

 

Terry

Share this post


Link to post
Share on other sites
oldlady    1,323

no, air doesn't do it.  water does.  water expands as it heats.  if you are in doubt about the dryness of a piece, just put it in your kiln and set the controls to preheat.  you can choose the length of time to preheat but my kiln rep says that the speed of getting it up to boiling, 212 degrees is so slow that the hold time of 15 minutes is enough.  i assume you are not trying to fire a brick thick item or a bowling ball.

 

if you really worry about that piece that exploded, look at closely and see if you can see how thick it was.  new throwers make very thick bottoms without realizing it.  when you start throwing, cut the pots in half downward and check the thickness.  remember that when you are starting out you are learning a skill, not making a product.  cut down ten or so and get familiar with the feeling of the thickness.  don't get hung up on making something until you can do it well.

Share this post


Link to post
Share on other sites
Min    784

Okay so the rule about air bubbles isn't true? I live in terror of air bubbles exploding my ware! In fact I was at the group studio the other day and someone else's piece was laying on the kiln room table in what was shards basically. I asked what happened, thinking maybe the clay had not been dry enough to bisque since it was quite a thick piece. I was told that no most likely they had used reclaimed clay and not properly wedged it so it had air bubbles and that's why it exploded.

 

So ARE air bubbles a major issue? Or am I wasting my time wedging my clay until my arms are numb? I should also state in full honestly that I am also terrified of firing possibly damp pieces so often keep them for weeks before firing just to be sure they are dry. The "it will feel cool if damp test" doesn't work when it's been raining for so long I am considering purchasing an ark.

 

Can you tell by looking at an exploded piece what caused it?

 

Love this topic by the way I am learning a lot.

 

Terry

 

Air bubbles don't cause pots to explode but they do have a nasty habit of showing up in the finished ware. Pots with rolled rims have a lot of air trapped but don't explode (if dry when fired).

 

If you put a greenware piece against your cheek it should not feel cold, but cool is okay if the pots are drying in a cool room. If in doubt candle the pieces overnight with the lid propped open a couple inches. I know it's unorthodox but I have also dried pots in the kitchen oven, 175F with the door propped slightly open with a knife blade.  

 

What kind of wedging do you do to make your arms numb? Do you have your wedging table at the correct height? I'm 5' nothing and use a horizontal filing cabinet to wedge on that's about hip height. 

Share this post


Link to post
Share on other sites
Claypple    29

 

 

 

Figures! Are you still using a sofa to sit on when you throw?

 

Naw, I've moved on to a padded desk chair.....I'm serious.

 

 

What is next? A rolling chair?  :)

Share this post


Link to post
Share on other sites
Pugaboo    438

Min - You have to remember I am NEW it took me quite awhile to figure out how to wedge properly. I think for awhile there I was adding more air into the clay than out of it. At first I used the wrong height and had some issues with my hands and wrists. So I got a low step to stand on to get my work surface to hit at the proper height.

 

I did discover something the other day which made it much easier for me to wedge reclaimed clay. I keep all my scraps in 2 gallon ziplock bags. When a bag gets full its time to reclaim it. I usually just spray some water inside the bag at the end of each session then when I wedge dump it out and start wrestling with it.

 

Well a few weeks ago I decided to just dump some of my clay water into the bag instead. After doing so realized I had added too much so let the bag sit for about a week. I then took the bag with it sealed up and just started dropping it on the floor flipping and dropping it repeatedly to work the extra moisture into the clay. Every few drops I would let some air out then squeezing it tight to remove the air seal it up and drop some more. After a few times of this I dropped and shaped the clay inside the bag into an approximate ball then rolled that out of the bag onto my canvas covered table. It was still a bit soft and sticky but started wedging it and within a few times realized it was so much easier to wedge the softer clay. I mean really easy. It only took a little while for the clay to firm up and not be sticky. By the time it was firm enough to use I cut it in half to check for air bubbles and found none. I was amazed because it had never been so easy before. From now on I am going to make my reclaimed clay a bit wetter to start with since its easier on my hands. I actually found I could control the wedging movements better thereby getting a much nicer air bubble free clay much quicker doing it this way. I don't know if its the proper way to do it but for the moment it's working for me.

 

Oldlady - I haven't started throwing yet and am just doing coils, pinch and slab for the moment and am very much aware of my thicknesses at all times. I tend to be very precise, too much so at times I think since I can measure and trim a piece to death to get it perfect all the way through. I am working on this trying to loosen up a bit and let the clay live a bit more rather than controlling it down to a hairs breath. I make maquettes of just about everything then also make a cardboard template to use to cut the pieces out so everything starts out as precise as possible. I keep these labeled and ready to go for future pieces so i dont have to remember what size or how i assembled something.

 

Early next year I will be taking a throwing class and will have to learn about telling how thick a piece is that way which ought to be interesting. Cutting the pieces in half sounds like an excellent idea to see exactly what is going on inside the piece and will make sure to utilize this once I start thanks. Oh and by the way yes I am a leftie too but then so is my teacher which will hopefully make it easier on both of us during class.

 

 

I tell people lefties are more creative we have to be to live in a right handed world!

 

Terry

Share this post


Link to post
Share on other sites
jrgpots    231

6 years ago I was given a small programmable kiln. I was reassured that since it was computer controlled it didn't need to be watched.....you guessed it. One fried mother board, one garage fire later; and $139,000 poorer, I learned that that was not a good rule

Share this post


Link to post
Share on other sites
Benzine    610

 

 

 

 

Figures! Are you still using a sofa to sit on when you throw?

 

Naw, I've moved on to a padded desk chair.....I'm serious.

 

 

What is next? A rolling chair?  :)

 

It does roll.  It's an adjustable height, padded, rolling chair, you'd use at a computer desk.  Though, to be fair, I bought it in college, and my backside has done a good job of wearing down that padding.

 

6 years ago I was given a small programmable kiln. I was reassured that since it was computer controlled it didn't need to be watched.....you guessed it. One fried mother board, one garage fire later; and $139,000 poorer, I learned that that was not a good rule

There is learning the hard way, and then there is what happened with you........Wow!

I'll be honest, I've left a couple programable kilns unattended, in my classrooms.  Though, I do usually give a heads up to the custodial staff, something along the lines of "If you smell smoke....."

 

I think the air bubble myth is one that should continue to be propagated, at least in the classroom setting.  It really forces the students, to take care, when handling their clay.  If you tell them, there is no consequence for sloppy preparation and construction, there will be issues.  If they are told, that their project will explode, and it will effect their grade, they will make sure that clay is well mixed/ wedged, before starting. 

 

Also, as I understand it, the reason some ceramicists are concerned over air bubbles, is because the bubbles allow steam to build, in those spots. 

Share this post


Link to post
Share on other sites
OffCenter    82

Pugaboo, the air bubble myth will always be with us (especially if teachers use Benzine's reasoning!) because of the example you gave of some lame-brained instructor telling students that some thick, not completely dry piece blew up because of air bubbles. BUT, just because air bubbles do not cause pots to blow up doesn't mean you don't need to get rid of them. They interfer with throwing (or rolling slabs, etc.) and, as someone has already mentioned, show up in the finished pot and look like a tumor. If you're having trouble wedging, maybe try a different way or use both the kneading and cut-and-slap method. I think the cut-and-slap method when done properly is better at removing air. I start by doing that then finish with spiral shell kneading.

 

Jim

Share this post


Link to post
Share on other sites
OffCenter    82

6 years ago I was given a small programmable kiln. I was reassured that since it was computer controlled it didn't need to be watched.....you guessed it. One fried mother board, one garage fire later; and $139,000 poorer, I learned that that was not a good rule

 

Sorry to hear about that! My kiln shed caught on fire once, but I saved it and even if I hadn't it would have only cost about $1,000 to replace it. The problem was that the plug on the small kiln had worked lose and caused and arc. I've never heard of a kiln actually causing a fire because the kiln would just burn out before doing something to cause a fire (unless the potter did something really stupid like placing the kiln too close to something flamable). Was your fire caused by the wiring?

 

Jim

Share this post


Link to post
Share on other sites
OffCenter    82

Come on, Benzine! You're joking right?

 

"I think the air bubble myth is one that should continue to be propagated, at least in the classroom setting.  It really forces the students, to take care, when handling their clay.  If you tell them, there is no consequence for sloppy preparation and construction, there will be issues.  If they are told, that their project will explode, and it will effect their grade, they will make sure that clay is well mixed/ wedged, before starting."

 

You don't have to tell them there is no consequence for sloppy preparation because poorly wedged clay causes enough problems without having to make something up.

 

Jim

Share this post


Link to post
Share on other sites
Benzine    610

Come on, Benzine! You're joking right?

 

"I think the air bubble myth is one that should continue to be propagated, at least in the classroom setting.  It really forces the students, to take care, when handling their clay.  If you tell them, there is no consequence for sloppy preparation and construction, there will be issues.  If they are told, that their project will explode, and it will effect their grade, they will make sure that clay is well mixed/ wedged, before starting."

 

You don't have to tell them there is no consequence for sloppy preparation because poorly wedged clay causes enough problems without having to make something up.

 

Jim

Well, I can always ammend my spiel a bit.  And I will be honest, I've propagated the myth for so long, because that's what I learned....In fact, I think my college text book mentions it. 

 

Tell you what, I'll stop spreading the myth this year....It will counter balance the fact, that I'll be having my students trim on a Giffin Grip....muhahaha!

Share this post


Link to post
Share on other sites
Claypple    29

6 years ago I was given a small programmable kiln. I was reassured that since it was computer controlled it didn't need to be watched.....you guessed it. One fried mother board, one garage fire later; and $139,000 poorer, I learned that that was not a good rule

 

I think this is another myth, that the kiln can go on fire. The bad wiring will start the fire, not the kiln itself. Where is Neil to comment on this?

 

Benzine, how about a rocking chair? 

Share this post


Link to post
Share on other sites
Benzine    610

 

6 years ago I was given a small programmable kiln. I was reassured that since it was computer controlled it didn't need to be watched.....you guessed it. One fried mother board, one garage fire later; and $139,000 poorer, I learned that that was not a good rule

 

I think this is another myth, that the kiln can go on fire. The bad wiring will start the fire, not the kiln itself. Where is Neil to comment on this?

 

Benzine, how about a rocking chair? 

 

It tilts back a little, does this count?

 

Honestly, the main reason I'm using it, is because, it sits at the perfect height for my wheel.  No sense in spendingmoney on a stool, if I have a seat that already works.

Share this post


Link to post
Share on other sites
Chris Campbell    1,088

Pugaboo ... My goodness, you are working hard! You make my case for the fact that reclaimed clay is the most expensive clay you will ever use. Your attention to detail might make you a good candidate to join us colored clay crazies though! : - )

 

Air bubbles have never been a big issue for me ... I have had sculpture explode but it was no mystery since they were incredibly uneven in thickness and the explosion was almost expected.

I fire closed balls and garden rocks without air holes poked in them and haven't lost any. I think that rule depends totally on your clay body and firing temp.

I use a Giffen Grip whenever I feel like it and lightning has not struck me .....yet.

I do use a splash pan as I would look like a clay sculpture myself if I did not ... I am one messy thrower! I can get clay splashes on the back of my head.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×