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

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Bob Coyle    113

The amount of total energy you use is related to heat loss and thermal mass. If you figure that the heat losses through the walls of your kiln are about the same for a given ramp, then the total thermal mass will determine the energy expended.

 

Kiln hardware has a lot of thermal mass. So if you are firing a few thin walled vessels per shelf, then much of the energy will be going to heating up the kiln walls and furniture. Since the clay vessels and the kiln shelves probably have about the same heat capacity, you could probably figure out the ratio by just weighing all the fired pieces and then the kiln furniture. But why bother... your stuck with the furniture you already have. They make some strong thin shelves that you could use but they are pretty expensive and I am not sure where the break even point would be if you bought them.

 

So in terms of thermal efficiency it is probably better to load up an electric kiln as tight as you can get it and to stack your ware for the bisk firing,

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Mart    23

... So in terms of thermal efficiency it is probably better to load up an electric kiln as tight as you can get it and to stack your ware for the bisk firing,

My original "why" was asked because I believe it's not really good idea to stuff the kiln as tight as you can.

 

Looks like I am not alone. John has repeated this in multiple forum threads. Here is one: http://community.ceramicartsdaily.org/topic/5140-im-getting-pinholes-in-my-glaze/#entry46867

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neilestrick    1,379

I leave 1/8 inch between my pots, 1/4 inch between the pots and the shelf above. I've done it that way for 20+ years, and never had a problem.

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For glaze firings I leave about 1  thick piece of cardboard space between each piece. My kiln is so tiny that I can only fire 8-12 small pieces.  I pray to mark's picture ;)  

Now that Neil gave me the connection and I have a  bigger kiln, I am a bit nervous thinking about how it's going to stack up.  Many of the shelves that came with it have glaze on them.  Are they safe for bisque firing 04 since the glaze will not melt? Or do i need to start grinding those shelves? 

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neilestrick    1,379

For glaze firings I leave about 1  thick piece of cardboard space between each piece. My kiln is so tiny that I can only fire 8-12 small pieces.  I pray to mark's picture ;)

Now that Neil gave me the connection and I have a  bigger kiln, I am a bit nervous thinking about how it's going to stack up.  Many of the shelves that came with it have glaze on them.  Are they safe for bisque firing 04 since the glaze will not melt? Or do i need to start grinding those shelves? 

 

The glaze on the shelves may be low fire glaze, in which case it will re-melt during a bisque firing. Time to start grinding and washing.

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timbo_heff    37

One quick thought on this:

Even though you CAN stack your bique fire packed to max, it is not always a good idea:

Problems that rear their head during glaze fire such as pinholes and bloats, are  caused during the bisque fire.

One of the thing that makes these problems is insufficient oxegen presintering in the bisque fire.

When the bisque load is looser the air circulation and oxygenation are improved and thus burn out of organics is more betterer. (;

 

Not all clays need this but the ones that do, do. Usually it is the darker cone 6 and cone 10 clays that have more stuff to burn out.

All clays would be happy with more air, there is certainly no detriment except what you are doing in 2 loads, you may want to do in 3 loads.

Given that it is usually $15 or less to electric fire 7 feet of bisque, it is a small price to pay to prevent problems and have happier pots and not having to throw out pots with bloats and other issues.

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TJR    359

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

Mark;

I think I see a spot in the first picture, third shelf down where you could sneak a spoon rest bestween those two big bowls. Just kidding ya. Amazing stacking.

TJR.

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For glaze firings I leave about 1  thick piece of cardboard space between each piece. My kiln is so tiny that I can only fire 8-12 small pieces.  I pray to mark's picture ;)

Now that Neil gave me the connection and I have a  bigger kiln, I am a bit nervous thinking about how it's going to stack up.  Many of the shelves that came with it have glaze on them.  Are they safe for bisque firing 04 since the glaze will not melt? Or do i need to start grinding those shelves? 

 

The glaze on the shelves may be low fire glaze, in which case it will re-melt during a bisque firing. Time to start grinding and washing.

 

 

 

 

For glaze firings I leave about 1  thick piece of cardboard space between each piece. My kiln is so tiny that I can only fire 8-12 small pieces.  I pray to mark's picture ;)

Now that Neil gave me the connection and I have a  bigger kiln, I am a bit nervous thinking about how it's going to stack up.  Many of the shelves that came with it have glaze on them.  Are they safe for bisque firing 04 since the glaze will not melt? Or do i need to start grinding those shelves? 

 

The glaze on the shelves may be low fire glaze, in which case it will re-melt during a bisque firing. Time to start grinding and washing.

 

Blah-  but good advice. You never know so It's not worth it.  I got the grinding brick thing with the kiln.  

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