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Real Time Preheating Question

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I have a one-year-old electronic Olympic kiln.  I use the preset programs, always going with a slow bisque combined with a long preheat period -- usually 12-18 hours preheating at 200.  Tonight I need to rush this load a little, but I don't think it's ready for 200 degrees!  I'd like to dry the work a little faster than it can dry by just sitting in my studio (withits humidity of 85%).  It seems that PRE pre-heating the work at maybe 125 for 12 hours before I use the actual preheat program, which is 200 degrees, would be safer than jumping the temperature on the sculptures straightaway to 200. 

 

Is my logic, um, logical? And if it is, can anyone tell me how to do this?  I can't find anything in the instruction manual that tells me how to set the temperature to 125 degrees for a period of time.

 

Jayne

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You normally hold 200 for over twelve hours?!!! How thick/ wet are you wares generally, upon loading?

 

In my classrroom, I'll do a preheat for about four hours, which is normally adequate.

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Benzine, My sculptures tend to be a bit organic....which is another way of saying that they decide what they're going to be as we go along.  Let's say I build a person's head, then add hair, then add feathers, then add....., well you get the idea.  The attached image of a sculpture that stands about 25" high is a good example of that.  Even though I've cut open the head and scraped it out to try to make the walls 1/4" thick, the individual ropes of hair and in this case, feathers, makes it impossible to keep to that 1/4" thickness. 

 

Also, it's VERY humid here, so nothing is every really dry.  AND, I don't have the patience to wait the 2 or 3 weeks that some folk recommend for sculptural work.  I did read yesterday's posts about using a kiln to dry wet work, but it didn't really address this kind of work........

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post-1258-0-15904600-1403666460_thumb.jpg

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I would keep it under 212 degress no matter what kind of work as steam is steam no matter what the work is.

The question is really hold it under 200 until the moisture is gone and that will be a direct relationship to thickness and dryness.

Your work demands a long slow preheat k.

If its paper clay it can take a bit less time I think or any clay with an aditive that loosens it up.

How tight is this clay body?

Mark

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Mark, this is a raku clay body.  I chose it because I wanted a clay that was strong enough to survive my mistakes!  Also, the intention is to pit fire (well, trash can fire) my work....one of these days.  (My last pit firing was with an earthenware clay and it ended up broken into 8 pieces.  I really don't want to stand by a fire and hear that many pops and cracks every again!!)

 

Okay, I think I hear what you're saying, Mark.  I just thought that if I slowly raised the temp to 200, there would be less likelihood of fissures.  

 

 

Babs, you make me laugh.

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Jayne, Your sculptures tend to be a bit awesome...

 

That long of a preheat, still seems excessive, even if you work is a bit uneven, in regards to thickness.  I've seen some "heavy" unevenly thick Middle School work go in the kiln, but it always comes out just fine, sometimes to the chagrin of the creator, who didn't really want to have to deal with painting it...."Man, work!"

 

If the humidity is high in your area, what about creating a drying chamber of sorts.  Create a sealed chamber, hooked to a dehumidifier.  I've seen people post their method, for creating such a device.  It would save you time on your preheat.

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Thanks for the compliment, Benzine.  I'm afraid that I've kinda screwed that piece up!  I usually add copper carbonate to get dark tones to enhance the texture, but I've been experimenting with other glazes.  Yesterday I chose Stoneware Wash from Mayco as a paint on and rub off wash, and it went too dark.  Arrrgh!  Now I'm trying to figure out how to pull it back from the edge!  

 

Benzine, That's a good idea about using a dehumidifier.  I'll search for posts on the subject... 

 

I followed Mark's lead and went ahead and set the kiln to preheat at 200 overnight.  It hasn't hurt the work!! Yaaay!  So maybe I'll follow your lead and take a chance on shortening the overall preheat that I had planned on doing.  I'm going to try checking for steam via a mirror as has been mentioned here on the forum.  Unless there is a better way?

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I am sure the experts will disagree, but I have been using the mirror for 35 or more years.  a clear piece of glass from an 8x10 picture frame is my current choice.  all peephole plugs are out and the lid is cracked 1/2 inch until about 1000 degrees.  I hold the glass at an angle at each peephole and the edge of the lid to check for steam.  lid stays up until there is none.  lid down, peeps plugged and we're off.

 

I get steam at over 900 degrees sometimes.  remember that I single fire clay and glaze on each pot.  even though I have consistent thickness in each piece, they are only as dry as air in a very humid location can get.  and there are 9 or ten shelves tightly packed.

 

though you may fire less mass,  your work is thicker and might take more time.  I think, maybe.  experts chime in here, please.

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Benzine, the Mayco stoneware wash looked great before the piece went into the kiln.  The dark color was in each tiny, tiny groove on the feathers with the high areas between grooves wiped clean and showing the white clay.  As you can see by the photo, it didn't come out that way.  I'm guessing that the stoneware wash has to be really scrubbed off, and the feathers couldn't take that kind of abuse even after bisque firing. (?)  Odd that I could see the white clay between feather grooves before firing, though.  Ah well, live and learn.  I do like the metallic look of the wash, but I'll have to do some more experimenting before I subject another sculpture to it.  As a result of the dark wash obscuring the feathers, I have spent all day mixing a paint color that perfectly matches the original fired clay color and then painting with a super fine brush each teeny tiny, itty-bitty high ridge of each feather.  Not quite the way I planned things....!

 

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Thanks for the input, Oldlady.  I think I have a misunderstanding of the mirror test. I was trying to decide if the pieces were ready to move past that 212 mark without blowing up.  I was testing for steam with a mirror at a temperature under 212.  Duh!!

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Jayne, personally I think that looks great!  When you said that it was dark, I was expecting it to be stained REALLY dark.  I can see, what  you are talking about, in the hair/ feather portion.  But overall, I think it has a really nice, aged look.

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At 212F. Water just becoming steam, this is the lowest level water becomes steam.

I'm trying to figure out why everyone is suggesting lower temps.

 

Steam escaping through drier clay which is technically still open, Will cause explosions or deformity?? What damage will happen if semi dried pieces are Pre heated at 212 vs 200f

 

If held at lower temp 200 why not finish off at 212 to make sure....?

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At 212F. Water just becoming steam, this is the lowest level water becomes steam.

I'm trying to figure out why everyone is suggesting lower temps.

 

Steam escaping through drier clay which is technically still open, Will cause explosions or deformity?? What damage will happen if semi dried pieces are Pre heated at 212 vs 200f

 

If held at lower temp 200 why not finish off at 212 to make sure....?

 

Preheating lower than 212 F will dry the ware, but if there were moisture left and you go to 212, said moisture will turn to steam and make its way out.  This means the ware will either crack, or explode.  

You might be OK preheating at 212, because the ware could dry enough on its way up to 212, that nothing bad would happen.  But on the the other hand, why not preheat at a temperature, where the moisture can't possibly turn to steam, and save yourself a headache?

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I know this is off the topic a little bit, And I know you needed a rush on this piece, So I'm sorry aread of time for asking a newbie question...BUT..

 

Would packing sodium silicate around a piece of greenware or sculture dry it out more quickly and completely?.  And would packing it around a large sculture draw more water out of the piece than if the piece were left to air dry?

 

Basically could you dry clay sculture out more completely by packing them in sodium silicate?

 

Jed

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Hi Oldlady. 

 

I'm using Highwater Clay's Raku, cone 06-6.  I'm sure different effects would result from different clays.

 

The standing figure "Green Mansions" is bisque fired, then one coat of Mayco's "Stoneware Wash"  is applied diluted 1:1 with water. That is the specific glaze name given to it (also number 304, I think). It is then wiped off and fired to 4. (That glaze can be fired 06 to 10.)  In hindsight, I think I should have diluted it more.  It would have been easier to apply and maybe it would have stayed in the crevices rather than covering some nearby areas (the feathers' high ridges to be exact).  I'm afraid the color tone in the image isn't entirely true, because it is under fluorescent lighting.

 

For comparison, the head "Memories Become Bouquets" is bisque fired, then coated with copper carbonate mixed with water.  The excess is wiped off and the piece is fired to cone 5. (That's an arbitrary choice; I get almost the same results firing to cone 06 as to cone 6.)  Using copper carbonate wash on earthenware gives me a more iron look - what I call metallic - instead of mainly just brown color, as here.

 

I wasn't able to post pictures of the two pieces fully finished here, but for the finished sculptures, which have been washed with greatly diluted acrylics, see the next post. 

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Oldlady, as you can see, neither of the dark washes was obscured by the acrylics, although the Mayco wash is definitely more assertive than the copper carbonate.  Copper carbonate used this way is a little unpredictable, but I have added more cc to the water and gotten a darker effect, although not as dark as the Mayco "Stoneware Wash".  On the other hand, the Mayco "Stoneware Wash" may give a lighter effect if greatly diluted.  Time for more experiments!

.

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Jayne the eyes are phenomenal!

Are you seeking a metallic finish

Are you bisquing then applying to refire? Or to raw ware?

Sponging stuff off bisque ware can be effective, can sponge as hard as you like without destroyiin g texture, but it also can affect the colour of the exposed clay.

Just wondering for you!

ANd loving your work

A mixture of 3 parts manganese dioxide to 1 part black copper oxide plus water applied on clay or glaze gives a bronze metaliic finish which can be pretty attractive, be careful with the mang. though at least you know you're using it!

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Hi Babs.  Yes, I'm wanting a wash that has a metallic or "iron" look to it.  And it has to be applied to bisqueware since raw ware would likely lose a few details when I start rubbing & washing away excess wash.  There are times when I can't really scrub even the bisqueware because of areas that are too fragile.  I just bought a bottle of Amaco manganese dioxide wash, but it provided nothing but a dark, almost black color -- no sheen or iron look to it at all.  I'll give the black copper oxide and manganese dioxide mixture a try after my next visit to the clay store. Thanks!

Jayne

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