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PSC

Shiny Kiln Shelves?

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PSC    54

I teach at a community center. When i started teaching there was this pile of half shelves that were glossy. Frankly it looks like someone painted the shelves with clear glaze and fired them. The shiny surface has fractured off in some places. Now i am not all knowing about kilns, i know what i know but the world is full of stuff i don't know. So could this shiny coating on the shelves not be glaze but some kind of kiln wash i have never encountered? The kiln room in the past has been used to fire low fire slipware, porcelain dolls, and even glass slumping in one of the kilns before i started teaching there. I've avoided using them so far but we are kiln shelf poor and kiln rich, it would be nice to be able to use them. So anyone might have a clue what the shiny shelf coating is? Anybody have a guess at the best way of removing it?

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Bob Coyle    113

Shiny shelves don't sound good to me. Are they shiny on both sides? If not then I would try putting a really thick layer of kaolin or  kiln wash on them and fire them to the max temperature you will use. Put a small tripod stilt on one edge and see if it sticks to the shelf during the firing. If it doesn't you will probably be all right. Even if the shelves are covered with low fluxing glass, you can still use them if you dump enough kaolin on top of them to keep the glass from contacting thye bottom of your ware.

 

If they are shiny on both sides and it is due to low fluxing materials, then they will stick to any kiln posts you use. Stick a layer of kaowool on top of the posts. I think the only thing you can do is assume the worse and hope for the best that the shelves don't have anything that melts at the range you are firing. Then you have to try them out.

 

Good luck.

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Marcia Selsor    1,301

I would get out an angle grinder and grind the shiny stuff off the shelves. It is worth it.

 

Even if you have it on the bottom it could come off into your pieces or glue to your posts.

 

Get rid of it is the best thing to do, IMHO>

 

Marcia

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oldlady    1,323

i had this problem with shelves given to me.  i had a professional sandblaster try to remove the stuff and he could not.  

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Mark C.    1,806

This is where a photo would really help us?

I will wait to see these shiny shelves before suggesting what to do.

Mark

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If it is a fine, even-appearing shine/sheen, my guess it this, and my solution(s) follow: 

 

I've actually seen this many times during my 3 + decades as a pottery and clay sculpture teacher at studios that have been in operation a long time... Including those I taught in. Often, the bottoms of the shelves will become thinly and evenly "glazed" over several years of use via the glazes "fuming" minute amounts of gasses/glasses/glazes into the air as they as they melt and become molten. The fumes circulate around the kiln and adhere to the shelf surfaces (and posts and kiln walls too, to a lesser degree), building up over a long time. 

 

A kiln shelf that is not re-kiln-washed very often will also build this shine/sheen up on the kiln-washed surface, developing a sheen there, too. This will result in pots sticking regardless of how "dry" the foot is.

 

Often, this happens when the potters/students have gotten so good at glazing that they do not/rarely have drips, so the shelves are rarely resurfaced/re-kiln-washed. Or, the kilns have been used for low-fire ceramics, fired on stilts exclusively... 

 

If there is kiln wash under the shine/sheen on the "top" of the shelves, and you can't get a chisel to work, get out your powerful grinder (a Google of "hand held grinder concrete ceramic" should show you what I'm talking about). Take the shelves outdoors. Put on your heavy-duty dust mask and safety goggles and grind the sheen down. Then use a silicone carbide rubbing block to even out the surface. Wash both sides with water. Apply new kiln wash.

 

The shine/sheen remaining on the underside/bottom/un-kiln-washed surface will not be a problem unless you flip the shelves over... I noticed that little or no shine is seen where posts are placed under the shelves or on top, because the posts simply protect the shelves from the fuming. If for some reason the places on the undersides of the shelves where you wish to position your posts are shiny, simply grind those areas off, gently, being careful to not mess up the levelness. 

 

If no kiln wash is present/under the shine/sheen on either side of the shelf, try grinding one side and washing with water and applying kiln-wash and grinding (gently and carefully) the areas on the underside where you plan to position the shelves. Also, if firing, always give the shelf a tiny little sideways horizontal wiggle to detach any posts that may have fused to you shelves.

 

I hope this helps you get some use out of the shelves. 

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perkolator    54

Have a picture of them?  Is it on both sides?  What kind of shelves are they - high alumina clay or black carborundum?

 

It's also completely possible that someone mistook a bucket of glaze for kiln wash, but most likely this would only be on one side.  If these shelves were in a separate pile from all your other shelves, I'd kind of guess this may be the reason for them being set aside.  

 

I would personally do a test fire with one if I needed them - fire it and observe what happens, perhaps put a piece of clay on there to see if it fuses.  If it's glaze, that sucks, but you could try to grind it down a bit and then wash over with a good wash that will absorb some of the fluxing materials when fired.  Then wash it again and hopefully it won't stick to your pieces.

 

Good luck.

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PSC    54

Sorry it took a bit to get a photo. Here are 2 of the shelves. I hope you can see the shiny stuff.

post-59306-0-31873800-1381954947_thumb.jpg

post-59306-0-31873800-1381954947_thumb.jpg

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Mark C.    1,806

LOOKS to me like fluxed kiln wash-that is wash that was made with something that fluxed

or they where overfired for whatever wash was put on?

I would do either of two things depending on your budget

Replace with new and make a better wash

or grind this all off and make a better wash

This is what I use for wash

by wieght

1/2 alumina hydrate

1/4 EPK

1/4 calcined EPK

This wash will not flux at cone 11

It may be overkill for low fire applications.

Mark

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PSC    54

I didn't do this to the shelves. That how they were when i started teaching there. Its kinda weird cause its 2 different sizes. I would think if you fired one kiln and the shelves came out unexpected that you wouldn't fire the second kiln that had shelfs prepared the same. The kiln wash i use is the same I was taught in college and we fired to cone 10/11. Some of the stuff that i found when i started teaching were just odd...

 

Like the kiln room exhaust fan was hooked up to a thermostat. It wouldn't turn on til the thermostat somewhere in the fan shaft registered that the room was hot. So when winter came i could not get the fan to exhaust the fumes. I kept reporting it as nonworking and maintenance would declare it was fine. It took a meeting to find out why the fan wouldn't work and a couple of meetings to convince them it was fumes i needed to vent not heat.

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Bob Coyle    113

Those are some really used and abused kiln shelves.  I would try Mark's kiln wash first before you start grinding. Might as well try the easiest thing first. Do a test fire with a couple of  sacrificial pots on what looks like the worse section of the worse shelf. If they don't stick, you are probably OK to go.

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