Need to know Olympic 2831 gas amount for fire

[TallerJMC]

10 hours ago, MFP said:

I just saw something in the 2831 manual that might be of use.....there is supposed to be an inch opening between the shelves when loading the kiln.....to let the flame through. Didn't know if you were doing that. Thought I would bring it up as it is something I sure didn't know. 

Yes, I did that in first firing.  With 1” open in the middle  the shelves leave enough space towards the wall so that flames go up all the way to the top (kiln furniture was bought with the kiln, all Olympic).  Consequently bottom shelves did not reach temp. whereas at the top it did.

[MFP]

Please explain if you would why the stoneware  body remaining open at 6 would be a problem---except for using in ovens....that part I know?  I did get different temp clays.....and have test tiles made for all of them.  I can understand this where porcelain is concerned.....but since stoneware bodies are routinely used for raku at much lower temps...have a harder time understanding that one.  ( I do hate this "raku" body with grog that I got for the student....because it is used for raku it has a LOT of grog and is very unpleasant in many respects. You supposedly can use it for raku at 04, still open at 6 and vitrified at 10---but since it is a horror in many respects, I have ordered 25 pounds each of a laguna and clay art center white stoneware to try. )  I never thought I would see the day when the porcelains were the easy ones to chose. 

[MFP]

Hmmmm........I still think the idea of making the top and bottom tight....and the middle open, might  solve the problem--by thermodynamics alone if for no other reason.  I think that four burner design is just causing problems.....when I saw that they had changed to that, all kinds of problems immediately occurred to me. I am glad my kiln is old and has six burners that are probably also smaller, meaning that controlling the amount of gas going through them is easier and therefore, the temp. 

[neilestrick]

2 hours ago, MFP said:

Please explain if you would why the stoneware  body remaining open at 6 would be a problem---except for using in ovens....that part I know?  I did get different temp clays.....and have test tiles made for all of them.  I can understand this where porcelain is concerned.....but since stoneware bodies are routinely used for raku at much lower temps...have a harder time understanding that one.  ( I do hate this "raku" body with grog that I got for the student....because it is used for raku it has a LOT of grog and is very unpleasant in many respects. You supposedly can use it for raku at 04, still open at 6 and vitrified at 10---but since it is a horror in many respects, I have ordered 25 pounds each of a laguna and clay art center white stoneware to try. )  I never thought I would see the day when the porcelains were the easy ones to chose. 

For raku or non-functional ware it doesn't matter. For ware that is meant to be used for food or needs to be water tight, vitrification is necessary. If your clay is not tight enough, it will absorb liquids through the unglazed foot or through the glaze if it's crazed. That absorption can contribute to crazing, and it will weep moisture onto tables/furniture/cabinets, and could grow bacteria/mold/etc under the glaze.

[MFP]

Thanks Neil. I knew about the moisture absorption but did not think it would be to that extent.  I was already aware of the thermal shock issues.  It appears that my efforts to keep this uncomplicated are not working out very well!  Has everyone switched over to porcelain? I must admit that some of these porcelains are very nice. It seems all the folks on here are using porcelain.