Jump to content


Photo
- - - - -

How Much Of A Gap Between A Piece And Shelf Needed?


  • Please log in to reply
32 replies to this topic

#1 Pugaboo

Pugaboo

    Lifetime artist 2nd year potter

  • Members
  • PipPipPip
  • 314 posts
  • LocationHelen, GA

Posted 21 July 2013 - 10:36 PM

Still learning lots and have another question...
How much of a gap between the top of a piece and the bottom of the shelf do I need to leave?
Have heard/read squeeze it in as tight as possible all the way up to an inch because the pieces swell during firing so I am a bit confused.

Terry
The world is but a canvas to the imagination - Henry David Thoreau

#2 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,309 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 21 July 2013 - 11:58 PM

The clay will shrink in a glaze fire and a bisque fire if it keeps getting fired hotter.

So with that you only need it to clear the shelve the thickeness of a piece of paper.

Now if its a refire glaze piece than it can expand a bit with heat so its need more room.

Mark


Mark Cortright
www.liscomhillpottery.com

#3 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,046 posts
  • LocationCanada

Posted 22 July 2013 - 08:17 AM

I agree with Mark. You want to cram as much pottery as possible into your kiln. If it is a bisque, and since there is no glaze, pieces can be stacked on top of each other. For a glaze fire, you can stack right up to the lid. Use a yard stick across the top to make sure work is not higher than the kiln. Do not leave the yard stick in the kiln!

TJR.



#4 Pugaboo

Pugaboo

    Lifetime artist 2nd year potter

  • Members
  • PipPipPip
  • 314 posts
  • LocationHelen, GA

Posted 22 July 2013 - 08:27 AM

What if the piece has underglaze or RIO on it? Will either of those things make a piece stick to stuff?

Terry
The world is but a canvas to the imagination - Henry David Thoreau

#5 Benzine

Benzine

    Socratic Potter

  • Members
  • PipPipPip
  • 1,197 posts
  • LocationThe Hawkeye State

Posted 22 July 2013 - 09:05 AM

Underglaze won't stick, though it can leave some colored marks on the shelves and other pieces if you stack them.


"Anything worth believing, is worth questioning"

#6 Mart

Mart

    Advanced Member

  • Members
  • PipPipPip
  • 280 posts

Posted 22 July 2013 - 09:37 AM

I agree with Mark. You want to cram as much pottery as possible into your kiln. If it is a bisque, and since there is no glaze, pieces can be stacked on top of each other. For a glaze fire, you can stack right up to the lid. Use a yard stick across the top to make sure work is not higher than the kiln. Do not leave the yard stick in the kiln!

TJR.

 

Why?



#7 oldlady

oldlady

    firing an electric kiln to cone 6

  • Members
  • PipPipPip
  • 673 posts
  • Locationharpers ferry west va and pinellas park fl

Posted 22 July 2013 - 09:42 AM

so it heats evenly???  because the yardstick will burn up???  :rolleyes:


"putting you down does not raise me up."

#8 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,159 posts
  • LocationGrayslake, IL

Posted 22 July 2013 - 10:41 AM

The problem is during the glaze firing. Glazes bubble up as they melt, then smooth out. Too close to the shelf and they'll touch as they bubble. Give at least 1/8 inch. 1/4 to be safe.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#9 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,046 posts
  • LocationCanada

Posted 22 July 2013 - 02:15 PM

 

I agree with Mark. You want to cram as much pottery as possible into your kiln. If it is a bisque, and since there is no glaze, pieces can be stacked on top of each other. For a glaze fire, you can stack right up to the lid. Use a yard stick across the top to make sure work is not higher than the kiln. Do not leave the yard stick in the kiln!

TJR.

 

Why?

 

Because there is labour involved. It takes time to fire a kiln. The more you have in there the more product you produce. There are also energy costs involved with firing a kiln. You have to fire it up to the same temperature wether you have one mug in it or 83.Do you not pay for your firings?

T.



#10 erinwells

erinwells

    Newbie

  • Members
  • Pip
  • 4 posts
  • LocationMontrĂ©al

Posted 22 July 2013 - 03:49 PM

Wer... while I do agree that you can generally cram as much stuff as possible into a bisque, you generally do want to leave an inch or so between glazed pieces and shelves during a glaze firing.  It is true that overall, during both the glaze and bisque firing process the pieces do shrink, there are other factors that encourage us to leave a little room. You have a good shot and reducing a lot of cracking, dunting, and crazing if you leave adequate space for air to flow above your work during the firing as well as reducing the risk of a piece warping/bending and getting stuck to the bottom of the shelf above it. (In high fire some of my works have gone from bowl too "taco" and fused onto shelves above them) It also means you will have a more even firing! Generally speaking you will see more issues with larger pieces that do not have adequate space that will want to crack or warp if they don't have room...

 

I generally leave 3/4 inch room above the tallest piece on the shelf and, about a half-inch between pieces on the same shelf. 

 

PS, You are right that pieces do expand, but it is only for a little while near quartz inversion and is pretty negligible as the work has already decreased in size significantly. 



#11 OffCenter

OffCenter

    Advanced Member

  • Members
  • PipPipPip
  • 1,372 posts

Posted 22 July 2013 - 05:03 PM

You have a good shot and reducing a lot of cracking, dunting, and crazing if you leave adequate space for air to flow above your work during the firing ...

 

How so?

 

Leaving an inch is a waste of space. Neil's suggested spacing is what I go with when I need to pack a tight kiln.

 

Jim


E pur si muove.

"But it does move," said Galileo under his breath.

#12 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,046 posts
  • LocationCanada

Posted 22 July 2013 - 05:45 PM

Newbie;

As I have stated twice previously,you do not need to leave a large amount of space between your work. If your pieces are dunting and warping and turning into tacos, you have serious problems with your clay body in that you are firing it to too high a temperature. When loading a glaze kiln, you put the piece in so that it touches it's neighbour and then you move it away slightly. No more than 1/4 of an inch. No glaze pieces should touch. If you are firing a wood kiln or a salt kiln and you are wanting atmospheric effects, you can leave more space. For gas or electric, there is no need to squander space. Have you taken a look at Mark Cortnoy's pictures of his stacks? I don't think you could get a fettling knife blade between pots.

In these trying times of high energy costs, why are you firing air? Lets use our kiln space efficiently, and walk softly on the back of Mother Earth.

There! Now I have said it. After three times I feel that I have thoroughly explained my position.

TJR.



#13 perkolator

perkolator

    Advanced Member

  • Members
  • PipPipPip
  • 278 posts
  • LocationCalifornia

Posted 22 July 2013 - 06:11 PM

really depends on the size of work and whether or not it's been fired previously.  if it's pottery and stuff shorter than say 24", then you can get away with a very small space like 1/8-1/4".  if it's large-scale sculpture with lots of mass then this is where i'd have at least 1/2" depending on the size and clay body if firing greenware (my students are loading 2-6ft sculptures though).  when clay heats up it goes through quartz inversion and the molecules can expand 1-2%.  this is why you've been told to leave a space.  my general rule of thumb for most small items is if you can stick a piece of paper or cardstock between the objects then you're good to go!



#14 soilandpolish

soilandpolish

    Member

  • Members
  • PipPip
  • 13 posts

Posted 22 July 2013 - 07:44 PM

 How does heat-work tally up? If you fire and empty kiln to a temperature (or cone), and fire it again to the same endpoint full of wares, how much percentage wise more power is used? I think I'm having calibration issues with my sitter or I'd test instead of ask, but it seems to me, over my three firings so far, that the one full load took 400% longer to fire. I'm really unsure about the sitter though...

 

(Sorry if this is off-topic, but several posters mentioned filling the kiln to save energy.)



#15 Chris Campbell

Chris Campbell

    clay stained since 1988

  • Members
  • PipPipPip
  • 1,961 posts
  • LocationRaleigh, NC

Posted 22 July 2013 - 08:20 PM

Disclaimer .... i am not a firing genius ...
What I think you are asking is how much heat work is affected by mass. How much longer does a full kiln take over a partial one?
I used to stack my kilns like a squirrel hoards nuts ... It would take a lot of time to load and unload.
But now, I make larger pieces in weird shapes so have more air spaces.
I cannot say that it takes that much longer ... Certainly not hours longer.
Any other opinions or different results? My firing profiles have changed over the years so that might be what keeps it the same??

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

TRY ...   FAIL ...  LEARN ...  REPEAT


#16 bciskepottery

bciskepottery

    Advanced Member

  • Members
  • PipPipPip
  • 1,259 posts

Posted 22 July 2013 - 09:06 PM

I generally leave between 1/4 and 1/2 inch between the top of the wares and the next shelf, both bisque and glaze firings in an electric kiln.  Clay both expands and contracts during a firing, so the wares need some breathing room.  Plus, for glaze firings, you need to be aware of your glaze properties.  Some glazes spit and can contaminate wares next to them.  Some glazes flash fumes (copper glazes); so you don't want them fuming on a white vase or on one you decorated for hours with underglaze and then glazed in clear.  Sometimes fuming is nice . . . but not always.  And as Neil noted, glazes boil and bubble. 

 

Packing a full kiln is good practice, but allow some room for heat (electric kiln) and/or flames (gas or wood kiln) to move among the wares.  Especially on fuel kilns, that flame whipping/winding through the wares on the shelves creates beautiful effects.  Packed to closely, you end up blocking the flames. 

 

I don't recommend touching wares and then backing off to space them . . . it's a good way to leave a deposit of your favorite iron red glaze on a celadon vase.

 

Kiln loading (like most things in pottery) can be an art unto itself . . . you really get better, more efficient, and more knowledgeable the more you do it.



#17 oldlady

oldlady

    firing an electric kiln to cone 6

  • Members
  • PipPipPip
  • 673 posts
  • Locationharpers ferry west va and pinellas park fl

Posted 22 July 2013 - 09:11 PM

the above post was typed faster than mine and so it might appear that i read it before starting this.  not true.

 

all kinds of info here so i guess it is ok to add another opinion or two.  i have always used an electric kiln.  i pack the stuff in, using up to 9 full shelves per firing.  it all works fine.  anything that i don't like was something stupid that i did, not the kiln, clay or glaze. it is not packed paper tight, maybe pencil size spacing.  i do not have a kiln vent.  i close it all up after about 1000 degrees or so.  the heat is radiating inward from the heating coils inside the bricks.  radiant heat must have heat waves.  any info that is useful re how the waves travel?

 

in 1979 or so, the pres of the kiln club in wash dc did something bad to her leg and i loaded her gas kiln for her. it was the same size and shape as a large electric kiln, not a catenary arch or some such so i wasn't afraid to load it.  she made all kinds and sizes of stuff.  i loaded it full and stacked things on half shelves that hung over other work and made it all fit.  she said it was one and a half times more than she would have fit in the kiln and  the best firing she had done because the flame had to travel all around before exiting. that is what happens in gas and flames and air move during the firing.

 

the original poster has a small electric kiln with 15 inch half shelves.  this was her second attempt at firing and it was a bisque load.  most pieces were about the same size but there was one really tall piece she was trying to fit in and around. i know she did not mention all this in the post. she has an instruction manual from the kiln manufacturer and all kinds of "advice" from other sources.  

 

she does have a kiln vent so maybe air does move around inside HER kiln.  as far as i know, (agreed it isn't much)  nobody has climbed inside an electric kiln and watched how the air moves during a firing.  that info might be helpful, any volunteers? short of that, how does anybody know anything about this stuff?

 

there is a lot on info out there today and some of it belongs in chris campbell's post about the worst thing you ever heard. it is hard to know what is right in each situation.   what works for me might not for someone else. don't be afraid, newbies, it will some day become as familiar as your toaster. 


"putting you down does not raise me up."

#18 Mark C.

Mark C.

    Advanced Member

  • Members
  • PipPipPip
  • 2,309 posts
  • LocationNear Arcata Ca-redwood rain forest

Posted 22 July 2013 - 10:08 PM

This is what works for me as far as  glaze loads-I have mainly two size (nerds) shelve spacers which add a little to the stilt height . Mine are 5/8 and 3/4 inch small pieces of silicon carbide or mullite shevles. I have a few 1/4 ones but they die quickly due to fuzing no matter how much I coat them.

This glaze fire was just loaded a few minutes ago-my Third since the fourth of July -my 16th this year in my  35cub.car kiln. I have also done 12 small kilns this year in a 12 cubic updraft (firing now) and this loading is what works for me the past eons

This particular load is a bit odd as some of the forms are not my usual and take more wasted space (cannisters and a large 18 inch bowl)

This load has 36 12x24 inch advancers and is going to be fired in am to cone 11- 1/2 way down gas reduction fire in AM.

I place the pots so they almost touch and have forever with no sticking to one another. Refires will expand more and need more space as you can see they are a few in this load. As far as top space as close as I can get a shelve to clear with my nerds is what works for me all these years.

For those of us who make a living at this more in each kiln load is a key point. This may not work for everyone but it does for me which is what counts. My glazes do not expand more than almost touching the next item/shelve.

Every few years I will stick a pot to another-usually because I have shoved them together after loading them by moving them after placing them the 1st time around around. When you load a kiln like this many times all this is second nature-how tall of a stilt is needed what is the hieght of wares etc.This kiln loads in about 1 to two hours depending on how much small stuff is in it-I'm not a numbers guy counting pots but there is over 400 pieces in this load I'm sure.

Mark

 

 

Attached Files

  • Attached File  gl1.jpg   26.57KB   17 downloads
  • Attached File  gl2.jpg   19.92KB   7 downloads

Mark Cortright
www.liscomhillpottery.com

#19 oldlady

oldlady

    firing an electric kiln to cone 6

  • Members
  • PipPipPip
  • 673 posts
  • Locationharpers ferry west va and pinellas park fl

Posted 22 July 2013 - 10:24 PM

i knew you worked hard, mark, that is crazy!  you make more pots in six months than i have in a lifetime. maybe more on one shelf.


"putting you down does not raise me up."

#20 TJR

TJR

    Advanced Member

  • Members
  • PipPipPip
  • 1,046 posts
  • LocationCanada

Posted 22 July 2013 - 10:25 PM

This is what works for me as far as  glaze loads-I have mainly two size (nerds) shelve spacers which add a little to the stilt height . Mine are 5/8 and 3/4 inch small pieces of silicon carbide or mullite shevles. I have a few 1/4 ones but they die quickly due to fuzing no matter how much I coat them.

This glaze fire was just loaded a few minutes ago-my Third since the fourth of July -my 16th this year in my  35cub.car kiln. I have also done 12 small kilns this year in a 12 cubic updraft (firing now) and this loading is what works for me the past eons

This particular load is a bit odd as some of the forms are not my usual and take more wasted space (cannisters and a large 18 inch bowl)

This load has 36 12x24 inch advancers and is going to be fired in am to cone 11- 1/2 way down gas reduction fire in AM.

I place the pots so they almost touch and have forever with no sticking to one another. Refires will expand more and need more space as you can see they are a few in this load. As far as top space as close as I can get a shelve to clear with my nerds is what works for me all these years.

For those of us who make a living at this more in each kiln load is a key point. This may not work for everyone but it does for me which is what counts. My glazes do not expand more than almost touching the next item/shelve.

Every few years I will stick a pot to another-usually because I have shoved them together after loading them by moving them after placing them the 1st time around around. When you load a kiln like this many times all this is second nature-how tall of a stilt is needed what is the hieght of wares etc.This kiln loads in about 1 to two hours depending on how much small stuff is in it-I'm not a numbers guy counting pots but there is over 400 pieces in this load I'm sure.

Mark

Thanks for this, Mark. A picture is worth a thousand words.

T.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users