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Mixing Black Clay Body - Cone 10 - Need Expertise


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 Looking to mix up a nice black clay body that will fire well at cone 10 with a 10-12% shrinkage.

 

 Short story long..., been taking a class and my instructor has a nice black clay body he uses for slab work. It's the 'studio mix' (a blend of whatever cone 10 clays used ... Laguna's mainly I think, CA-2, Bmix, etc... that are recycled from classes, then he adds about 50% C red and Grog.).

 

 I tried to throw it but he uses 30 mesh grog and quite a bit of it so it was  just a brutal throwing. Really rough on the hands just to center.

 

 So we discussed mixing clay and he set me off to mix up the same clay body, just with less grog and I used 60 mesh instead.

 

 It throws great. I mixed 50 lbs and threw some really great stuff, really focused on throwing thin wall, nice forms , etc.. Really put a lot of work in. Glazed one piece and while it was in high fire started mixing another batch. (was using an rarley used white shino.. it was for a show). The other pieces I held off on due to timing...

 

 So it comes out of the kiln, goes into the show and a few days later has massive cracking all around the piece. By now all my other work is glazed and being fired. (this is all now chipping and breaking - clay shrinking more than glaze?)

 

 The instructor NOW mentions he adds about 10% Feldspar to his mix, that I should have done tests and it was an 'expiremental clay body'. I feel like he sabotaged me. Why would he fail to mention this critical element as he watched me work hard for a few weeks, then mention it as if it was noi big deal?

 

 So I am down 2-3 weeks of work that was supposed to stock a gallery for the summer (busy season is hitting now and I am completely broke, living on scraps to try and make this work)..

 

 I have completely lost faith in him and don't trust his advice at all so I am looking for help to develop a black stoneware that is balanced with 10-12% shrinkange rates.

 

 At the studio I have access to the basics (Feldspar, frit, c red clay, iron oxide  etc..) but in recipies online there are often 5+ components of very specific names.

 

 Here is a pic of the first piece I lost, fresh out of the kiln before the cracking started . Had several interested parties straight out of the kiln so it was a real blow.

post-13458-0-43699800-1405153443_thumb.jpg

post-13458-0-43699800-1405153443_thumb.jpg

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What is your firing schedule? What temp did you pull ware from kiln? How did you bisque? What atmosphere?

 

Is crazed? Is it shivering? Are you familiar with COE

 

What clay recipe are you using? Any pics of cracked up pieces? Is clay vitrified? Is this gas fired?

 

Ever consider glaze doesn't fit body? Maybe consider getting glaze to fit body?" If it's a proper shino which it looks like.....you have up hill task. Some will say it's easier to fit the clay to the glaze. Meaning reformulate clay

 

Even the mix your instructor uses is in consistent. A blend of........ I'm not saying you can't get a good clay from "the bucket"... But it will never be the same batch to batch.

 

You will never get a consistent clay body unless you mix from known ingredients and quantities.

 

Too bad your clay and glaze isn't working. Your building form,and technique, and overall aesthetic is quite good.......

 

There are resources to find your solution but will need testing

 

 

Your not going to like this next part.....

 

But you have to understand the some of the chemistry....

If you want good results you have to run tests often lots of them.

It's quite rewarding to formulate your OWN clay body.

Pottery is not a sport for the impatient

The idea of a building an "inventory" on untested materials is a bit. Crazy.

And if don't want to "test". Aka "work".... You want quick and free solution you want it now.You'll probably not find many willing to help you. ( fill in sucking from welfare teat analogy here )

In the real world if a business ran into. This problem during production. They'd hire a HIGHLY PAID ceramic consultant. Some who post here.l

If you actually work out this issue you'll beat a much better potter in the long run.

 

Potential solutions:

A. Go back to known clay mix your instructor is using. Keep the grog just change the size . Using same quantity of grog use 50%coarse 10 medium 40 fine.(this comes from notes from college lecture). Or just lower the coarse percentage and add 48f. Or 50f grog for balance. This should get you close softer throwing clay and possibly maintain CTE/COE of original body. And maintain original results with softer body.

 

B. Tough it out and throw with original clay

 

C. Hint "Alfred". There are Internet sources that list black clay body recipes. (These too will need testing with your current glazes)

 

D. Listen to you instructor. I wish I had one. (no disrespect to my on line teachers here)

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Guest JBaymore

There is an element here of one "classic" mistake I see undergrad students (and occasionally grads) make all the time.

 

Cutting to the chase....... it is making a large body of work, being fully committted to it... making lots of pieces, putting in a lot of labor.........BEFORE the necessary technical work to understand the materials and how they are working (and know that results will be consistent) has been done.  PARTICULARLY right before a major critique/show/ etc. deadline is happening. 

 

Big surprise...... comes out of the kiln with unexpected results.

 

We unfortunately work in a "technical media".  It is usually not enought to just have the artistic side.... you also usually have to have at least a bit of the technical side under control.

 

This was one of those "life lessons" we ALL get in working with clay.  Powerful... but painful.

 

best,

 

..................john

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>The instructor NOW mentions he adds about 10% Feldspar to his mix, that I should have done tests and it was an 'expiremental clay body'. I feel like he sabotaged me. Why would he fail to mention this critical element as he watched me work hard for a few weeks, then mention it as if it was noi big deal?<

 

I see you want to shift the blame to your instructor. It might work with your friends, but not with people who have been there, done that and have the t-shirt.

 

Yes, we have all run over similar cliffs and learned to test first, production throw later.

 

Best bet would be to make some income generating forms with clays and glazes you know work. Then with that money start investigating and testing the new black clay body.

 

A new black clay body that works is not something you are going to achieve quickly.

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I see you want to shift the blame to your instructor. It might work with your friends, but not with people who have been there, done that and have the t-shirt.

 

 

I don't know Chris. Yes, Rebel_Rocker should have run tests prior to going into production but for the instructor to watch them work for 3 weeks without any guidance or questions is a bit rough. It takes experience to know enough to test thoroughly first, when you haven't done something before you don't know what you don't know.

 

Sucks now but in hindsight you will have learned something invaluable. 

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 Well, my instructor has been at this for 20+ years and like I said,

 

 He gave me the recipe to his clay body (well, he told me he mixes in 50% red C, didn't mention feldspar) but I just used a finer grit than he used (by his council). But he failed to mention he adds 10% feldspar.

 

 Sorry Chris but I don't think you are right about me shifting the blame. I am paying for his instruction, if this was not what he uses or if saw issues he should have told me to test. He was adamant I test a small coil for color (which I did). He never said there was ANY reason to question him and test glaze fit. I've seen many pieces he used that the glaze was fine on.

   If a professional baker gives you a cookie recipe but leaves out sugar is it your fault they aren't sweet? Is the first thing you think of is to question the pro's recipe and start a barrage of tests with random ingredients and hope you find the right one? I had no idea I needed Feldspar, that's why I aksed him what I needed.

 

 Now sure, if I had just gone off on a wild tangent and started mixing stuff up and expecting good results it WOULD be my fault and I WOULD need to test.

 

 But he gave me the impression that he gave me the correct recipe for the clay body he uses. He did NOT.

----------

 

 So that IS my goal, to reformulate the body to work with the existing glazes as he does.

 

 I can't give an exact account of the clay body mixed because it is a studio mix (they recycle like 1+ ton a year... it's a stable mix and he adds certain elements like a minor percent of C2 red to keep the red body red (and white scrap is also used). And I have no problems with that mix.

 But when I added 50% red C (dry clay) my clay shrinks too much. Now I know I need feldspar.

 

 Guess I'll just start mixing and testing, but this time I'll KNOW it's a test.

 

 And I have learned my lesson, just because someone is experienced and a paid instructor doesn't mean theire advice is worth taking. This isn't the first time he's given bad advice but it's the last time I take it.

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What is your firing schedule? What temp did you pull ware from kiln? How did you bisque? What atmosphere?

 

Is crazed? Is it shivering? Are you familiar with COE

 

What clay recipe are you using? Any pics of cracked up pieces? Is clay vitrified? Is this gas fired?

 

Ever consider glaze doesn't fit body? Maybe consider getting glaze to fit body?" If it's a proper shino which it looks like.....you have up hill task. Some will say it's easier to fit the clay to the glaze. Meaning reformulate clay

 

Even the mix your instructor uses is in consistent. A blend of........ I'm not saying you can't get a good clay from "the bucket"... But it will never be the same batch to batch.

 

You will never get a consistent clay body unless you mix from known ingredients and quantities.

 

Too bad your clay and glaze isn't working. Your building form,and technique, and overall aesthetic is quite good.......

 

There are resources to find your solution but will need testing

 

 

Your not going to like this next part.....

 

But you have to understand the some of the chemistry....

If you want good results you have to run tests often lots of them.

It's quite rewarding to formulate your OWN clay body.

Pottery is not a sport for the impatient

The idea of a building an "inventory" on untested materials is a bit. Crazy.

And if don't want to "test". Aka "work".... You want quick and free solution you want it now.You'll probably not find many willing to help you. ( fill in sucking from welfare teat analogy here )

In the real world if a business ran into. This problem during production. They'd hire a HIGHLY PAID ceramic consultant. Some who post here.l

If you actually work out this issue you'll beat a much better potter in the long run.

 

Potential solutions:

A. Go back to known clay mix your instructor is using. Keep the grog just change the size . Using same quantity of grog use 50%coarse 10 medium 40 fine.(this comes from notes from college lecture). Or just lower the coarse percentage and add 48f. Or 50f grog for balance. This should get you close softer throwing clay and possibly maintain CTE/COE of original body. And maintain original results with softer body.

 

B. Tough it out and throw with original clay

 

C. Hint "Alfred". There are Internet sources that list black clay body recipes. (These too will need testing with your current glazes)

 

D. Listen to you instructor. I wish I had one. (no disrespect to my on line teachers here)

A: IS what I did. He gave me wrong ingredients.

D: again, was the problem, I listened and it all failed.

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   If a professional baker gives you a cookie recipe but leaves out sugar is it your fault they aren't sweet? Is the first thing you think of is to question the pro's recipe and start a barrage of tests with random ingredients and hope you find the right one?

 

 

Yes to both.  A hard lesson I've had to learn is that most glaze and body recipes you see around in books, magazines, and on the internet don't work right out of the box.  Always test/tweaks.  First rule of cooking is never serve to guests what you've never cooked before.

 

I know that sucks to hear, but doing so will never steer you wrong.

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>   If a professional baker gives you a cookie recipe but leaves out sugar is it your fault they aren't sweet?>

 

YES ... even in the kitchen you should question and test. Heck, it could have been a misprint or the chef simply forgot to write it down. It is up to YOU to test or at least know enough about the ingredients to see a main one is missing.

 

That said ... this whole episode is a great LEARNING experience.

 

1 - Don't accept anyone's advice without question.

2 - Don't make a whole bunch of stuff with un-tested material.

3 - Sometimes your instructors do NOT know what they are talking about.

4 - Sometimes your instructors are simply repeating something they were told and it's wrong.

5 - YOU are responsible for what you do.

 

Almost every single thing my first pottery instructor told me was W R O N G !!

She simply filled in the blanks with opinions rather than facts and yes, was getting paid for it.

 

I had an email a couple years back from a clay student getting ready for the big 'Degree Show" ... he had made a complete vehicle out of clay by taking one apart and casting all the pieces ... the whole point being to make an exact replica ... but he had not factored in clay shrinkage and wanted to know if there was anything he could do  to prevent shrinkage so this car would be the right size.

 

I was simply stunned that no one had reminded him of shrinkage ... he must have worked on this for months in front of students and teachers. How could no one have noticed? I have no idea how the firings went, but best case is he was left with a 15 - 20 % smaller vehicle which I still think is a fairly great achievement even though it was off his plan.

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Guest JBaymore

One thing I have leared from teaching for 40 some years is that when you hear a story being told by someone else about what transpired... you are not always getting the 'whole picture'.  You are getting a single viewpoint on the genesis of the situation.   

 

Sometimes what the student hears/sees and what the instructor was saying/doing are completely different.

 

It would be interesting to hear the instructor's side of the same story about how the situation reached this point.

 

Iverall, Chris summed it all up nicely in her posting above.

 

best,

 

.................john

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.......

D. Listen to you instructor. I wish I had one. (no disrespect to my on line teachers here)

 

A: IS what I did. He gave me wrong ingredients.

D: again, was the problem, I listened and it all failed.

The instructor NOW mentions he adds about 10% Feldspar to his mix,

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Interesting, not entering the who was in the wrong argument but if taking instruction, in many cases, the ware produced is not for sale as  the input of the instructor is part of the whole and so is not marketable as your work!

Often workshops are run on this basis or understanding.

If instead you are using a communal studio and the instructor mentioned is just a bloke casually giving off some gems then pos. different scenario.

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 OK, Chris' wording in the last post is pretty fair. Though #4: this instructor is well vrs and I really had no doubts in the advice at all.

 

 Anyway, yep, lesson learned, for now anyway. Guess I've always had a problem trusting someone when I probably shouldn't. It probably won't be the last time :(

 

 @Jbaymore, I hear ya. But this wasn't a case of 'mishearing' or not listening. I asked for advice and I payed attention. Instructor had nothing to say about me not listening and knows full well info was left out. Only says I 'should have known'. And knowing the instuct ego (I have been working 4-6 days a week for 2 years) if I had questioned tempers would have flaired. I understand his position, many casual students mess up, are corrected and immediately turn around and make the same mistake agian (within minutes or hours). I am NOT one of them and he knows this. I am taking this VERY seriously.

 

 @Babs, it is a 'open studio' pretty much run by the instructor in question. Not a 'random bloke' but not a workshop or under strict guidance (as far as my work is concerned). Previously thought of more as a mentor, now thought of more as a random bloke, lol. Hard to say. He is an instuctor and the most knowledgeable ceramisist/artist in residence, and yet I feel there is some underlying issues. I don't use the term sabotage lightly, but from how things transpired... When I started on this endeavor it was trusted guidance, at the end it was 'my fault for not knowing better'. He was adamant I test a coil for color (and we both knew that adding a ton of iron to the clay would make it 'black' which the test confirmed, but only he knew that his mix had feldspar and mine didn't) but never once mentioned I should test the body for glaze fit. Trusting his judgement lead me to believe it was safe to throw serious work.

 But our work is not similar at all and couldn't be mistaken as such so it's not a question of marketability/copying/cloning/etc..

 

---------

 Anyway,

 

 I will post some picks of cracked work tommorrow, but some specs on firing:

 

 Schedule is not specific. Bisque tend to be fairly frequent. Slow fired to cone 6 (electric with a very occasional gas for large loads) as to avoid issues with random works from many people. In 2 years I have only recently seen one 'exploded piece', more like cracked . It was  a plate that was used many many times over years to fire handmade beads on.

 

 Glazing is done as required. Once a week, rarely sooner. Sometimes 2-3 weeks. Really depends on glaze shelves being filled. Class schedules, work finished, etc..

 

 Cone 10, reduction, Gas.

 

 All clays used in studio are Laguna or studio red/white (mix of laguna cone 10's) or porcelin (never mixed into studio, wedged seperately). CA2, Bmix, WSO, (it's late, maybe a few others). C2 is added for red stoneware studio mix color. (grit, frit and feldspar may be added to 'revive' the studio mix).

 All glazes fit these bodies nice at cone 10.

 

 The load with pictured piece with white shino (worst of the batch) was cooled quickly. Something that the main instructor did and a secondary instructor fought (kept closing door).

 I also had a piece thrown with studio red and coated with 'my' black clay slip, then carved through and fired with no glaze, it has not cracked.

 

=============

 

  I appreciate everyone's input. If nothing else it may have helped me cool my vents and rethink the entire situation. I'm looking at this as more of a 6 year plan (I'm at year 2), it's just hard to lose that much work during busy season since I am broke and struggling to make this work. And maybe more so because I put my full trust and respect into someone who didn't deserve it, now I have to push on on my own. I also have to look forward to more resistance from him, If I don't ask his advice when working in the studio and testing new things.. I can only imagine...

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Possibly this instructor considers this his own R and D like the Mudslinger discussion about paper clay not shared in a common studio. I can't see a good teacher doing this misleading on purpose unless they really don't want to share the recipe.May be time to move on.

Marcia

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Guest JBaymore
 In this relationship/setting, for the instructor to deliberately share incomplete information without disclosure just strikes me as wrong. 

 

I and my colleagues (at the college level) frequently discuss how we gave a particular student some feedback on something........... and then later discovered that the person had taken that single piece of information and had ignored all the other things that they already knew about the ceramic process... and went off on a total "blinders on" tangent and did something totally absurd with that information.  And that action then of course "bit them in the butt"..........   And then they were flabbergasted that WE had given them that information.  (Eventually ,........ they usually see the context of what they did and how they screwed it all up.  Hindsight can be powerful.)

 

Maybe the instructor would have NEVER anticipated that this particular student would suddenly go off and produce a whole body of work with the untested reformulation and even plan on showing the work produced....... without taking all the knowledge that they already had about ceramics and doing things like the necessary TESTING WORK before ever doing such a thing. 

 

I again come back to the fact that we have NO idea the context of this whole discussion.

 

There are many "styles" of instruction.  In the US we geneally try to give "constructive feedback" and in some cases "prescriptive feedback".  In some cultures the norm is "destructive feedback".  I've heard tales of apprentices who had worked hard for a full day finding hundreds of the forms they'd made broken to bits the next morning with one single one left standing.  No other feedback.  Tough love.

 

I agree that if the instructor did this deliberately to cause the problem .......... NOT good.

 

best,

 

.......................john

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>I'm looking at this as more of a 6 year plan (I'm at year 2), it's just hard to lose that much work during busy season since I am broke and struggling to make this work. And maybe more so because I put my full trust and respect into someone who didn't deserve it, now I have to push on on my own. I also have to look forward to more resistance from him, If I don't ask his advice when working in the studio and testing new things.. I can only imagine...<

 

Might be a good time to revisit and possibly revise your six year plan. Your original plan was made by a person who is now two years older and wiser.

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Maybe the instructor would have NEVER anticipated that this particular student would suddenly go off and produce a whole body of work with the untested reformulation and even plan on showing the work produced....... without taking all the knowledge that they already had about ceramics and doing things like the necessary TESTING WORK before ever doing such a thing. 

 

I again come back to the fact that we have NO idea the context of this whole discussion.

 

 

 

 

 I worked on this stuff over the course of weeks, 4-5 hours a day (6 days a week) in the same studio as instructor open studio AND class time . Sitting at wheels where we could talk and look each other in the eye. Even discussing the forms (he complimented me on every one of them) as I went. It's the yearly student/instructor show (so I know he knew I was working on pieces for it, we discussed it). In fact the pictured piece was fired in time for the show only because he announced there would be one final firing for it.

 

 All my work isn't lost, I still have 5-6 on the shelf, change of plans, they just won't be glazed.

 

 But again, I didn't go off on a wild tangent, I just didn't test with any amounts of feldspar. This is the first time I have formulated a body and I did it to his exact specs. (at least the ones he gave me). He watched me mix it, he had me test  a coil for color (only), and I made about 10 test tiles with glazes (the test tiles haven't cracked). Then he watched me make 50 lbs of work and start mixing up another 50 lbs batch (as I still assumed his guidance was right) .

 

 This isn't something I did out of sight, it was with his guidance right under his nose and the process lasted several weeks with everyone in the studio asking me about it, etc...He was well aware of every single thing I did regarding this process.

 But at the end when it failed he said 'Well I do put 10% Feldspar in mine', 'You should have tested'.

 

 The only way I would have known I needed Feldspar would have been to have my instructor tell me, or to second guess and look up recipies online and try to formulate myself.

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Maybe the instructor would have NEVER anticipated that this particular student would suddenly go off and produce a whole body of work with the untested reformulation and even plan on showing the work produced....... without taking all the knowledge that they already had about ceramics and doing things like the necessary TESTING WORK before ever doing such a thing. 

 

I again come back to the fact that we have NO idea the context of this whole discussion.

 

 

 

 

 I worked on this stuff over the course of weeks, 4-5 hours a day (6 days a week) in the same studio as instructor open studio AND class time . Sitting at wheels where we could talk and look each other in the eye. Even discussing the forms (he complimented me on every one of them) as I went. It's the yearly student/instructor show (so I know he knew I was working on pieces for it, we discussed it). In fact the pictured piece was fired in time for the show only because he announced there would be one final firing for it.

 

 All my work isn't lost, I still have 5-6 on the shelf, change of plans, they just won't be glazed.

 

 But again, I didn't go off on a wild tangent, I just didn't test with any amounts of feldspar. This is the first time I have formulated a body and I did it to his exact specs. (at least the ones he gave me). He watched me mix it, he had me test  a coil for color (only), and I made about 10 test tiles with glazes (the test tiles haven't cracked). Then he watched me make 50 lbs of work and start mixing up another 50 lbs batch (as I still assumed his guidance was right) .

 

 This isn't something I did out of sight, it was with his guidance right under his nose and the process lasted several weeks with everyone in the studio asking me about it, etc...He was well aware of every single thing I did regarding this process.

 But at the end when it failed he said 'Well I do put 10% Feldspar in mine', 'You should have tested'.

 

 The only way I would have known I needed Feldspar would have been to have my instructor tell me, or to second guess and look up recipies online and try to formulate myself.

 

It seems like you are still hanging on to this idea that your cracked pieces are the instructor's fault. Did you mix the clay or did he? Did you make the pots or did he? 

 

If he mixed the clay and threw your pots, then yes it would be his fault. But he didn't, YOU did those things.

 

It is common knowledge to test before you proceed. This isn't just in ceramics, but in just about everything. Want to know why It is common knowledge? It's because if you don't know to test before proceeding, then you will learn very quickly because of mistakes like this. Thus it becomes common (moreover significant) knowledge to you. 

 

Maybe the instructor didn't think adding feldspar was important? Maybe he didn't realize for some other reason, maybe he simply forgot. Big deal, it's life. Stop whining, blaming other people, and hoping for immediate satisfaction and perfection. Don't blame the instructor for your bad pots. That is entirely on you, fair or not.

 

Regarding your glaze popping off your pots--that sounds like shivering. I worked with potter S.C. Rolf when his clay/glazes were shivering. Huge splinters would pop off overnight and be laying beside the pot in the morning. The clay and glaze are different in that the clay shrinks a significant amount more than the glaze when cooled, which pops the glaze off in large pieces sometimes, especially around corners, edges, or points of major stress. Interesting that this might happen with a shino, as many shino's are high in clay and generally craze. Also note that one glaze may fit great after testing but another may still shiver. Glazes have different materials and chemical makeup in them and thus inherently have differing characteristics. This is common knowledge too so heed the warning. 

 

Look here for more info on shivering. In this case it would probably be easier to adjust the clay body than the glaze. By the way, that shino you used looks fantastic on that clay body. You should share the recipe here for your fellow ceramic arts daily potters. Good luck with your clay body.

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S. Dean,

I agree that I think this is wrong too BUT instructors are now expected to share all their intellectual property rights with the university without compensation. I think we don't know the whole story on that end of this issue. On the other hand, I don't support misleading a student to mishaps.

Marcia

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I know a few people (myself included) who although they understand it is best to test they love to hope and dream  :mellow: Many times I have cursed myself in hindsight and slowly learnt to be patient with just about everything.

 

Still who doesn't like a good cut corner.

 

So this clay body is a mix of clays fired with 50% C red and 10% feldspar? What is C red?

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If the class was on developing clay bodies aka Big Lou then the instructor is certainly questionable or forgetful.

However if it's a general class or other and a student has an idea out of left field then yes guidance but not totally taking on the swing to the left.

Developing clay bodies  haven't done it but I'd be reading my butt flat and checking out a number of sources and testing. Evident here many times no free lunch and no easy trips. Spoon fed, what happens when the spoon operattor is not in the room?.

Body glaze fit knowledge might have to occur too.

All of us will have empathy but prob not sympathy.

The term was instructor, not educator, now our Benzine would have done the homework and tested then taught for his students! :)  so his students had success.

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