Babs

And still we are throwing awY lithium batteries.

In the Clay and Glaze section of these firums there is a post right at the op or near it titled Wild Clay.
@glazenerd is a great resource also.
Throws pretty well!

What about the stuff folk use to cover books? Clear or coloured, or the psuedo bench solash back stuff, both come in rolls at different widths so quite a variety of screen outs possjble.
Are you burning it off? Look out for fumes, taking off before firing , it could lift the underlying glaze if any.

A common culprit for these kinds of problems is too much water and/or not enough compression. 
Do you use lots of water during the throwing process? If a pool of water sits in the bottom of the form, as you throw, this can lead to cracking/blowout problems.
Compressing the clay, with a rubber kidney tool, is a good way to strengthen the bottom of the form.
As Bill suggests overworking a form can also stress the clay. Using a kidney tool shaped like your desired shape can reduce the amount of time your fingers are actually working the clay.

Looking closely, I can see pinholes that are clear. I can see others that are black. I will vote coffee.
Tom

Not sure   but blue for me,  I have to mix a little frit into the  blue underglaze so it stays smooth under the glaze. A little of the glaze if it is a non run clear would also sort this. As it is not all over your blue dec.  Could it be the rough patches are applied thicker when brush fully loaded? Or underglaze not stirred between brush strokes? 

Every firing will weaken the clay after the 1st fire. Can you make the lid and fire it alone-yes it will have an unglazed surface where it sits on shelve but that no big deal

Noticing there are tinges of green, glaze thinner? Near base edge of glaze and glaze flaw in handle. SG and glaze application of glaze same as in the testing in the alternative kiln? 
Re refiring the clay body, have you done this with the clay you are using previously?
If you post what claybody you are using, someone may have experience with this.

I rhink you inadvertently did a reduction firing. Easy to do in a small gas kiln.
Do you have time to refire one as a test making sure you have a  fully oxidised atmosphere? With that amount of copper I could get black pots without trying in my gas kiln if not careful re atmosphere.

I rhink you inadvertently did a reduction firing. Easy to do in a small gas kiln.
Do you have time to refire one as a test making sure you have a  fully oxidised atmosphere? With that amount of copper I could get black pots without trying in my gas kiln if not careful re atmosphere.

I rhink you inadvertently did a reduction firing. Easy to do in a small gas kiln.
Do you have time to refire one as a test making sure you have a  fully oxidised atmosphere? With that amount of copper I could get black pots without trying in my gas kiln if not careful re atmosphere.

I rhink you inadvertently did a reduction firing. Easy to do in a small gas kiln.
Do you have time to refire one as a test making sure you have a  fully oxidised atmosphere? With that amount of copper I could get black pots without trying in my gas kiln if not careful re atmosphere.

I rhink you inadvertently did a reduction firing. Easy to do in a small gas kiln.
Do you have time to refire one as a test making sure you have a  fully oxidised atmosphere? With that amount of copper I could get black pots without trying in my gas kiln if not careful re atmosphere.

Do you have a pyrometer to log your kiln progress through firing? 1 cone is not usual practice. A bank of 3 cones one below target cone , target cone and one above the target. A bank of cones on each shelf to see how the inside of  your kiln is behaving.
Good luck.

Do you have a pyrometer to log your kiln progress through firing? 1 cone is not usual practice. A bank of 3 cones one below target cone , target cone and one above the target. A bank of cones on each shelf to see how the inside of  your kiln is behaving.
Good luck.

I've used three potteries that had gas kilns inside. Good venting is a must. Unlike an electric kiln, a gas kiln can introduce deadly carbon monoxide into the space. A carbon monoxide sensor alarm is important. It also seems that the heat given off by a gas kiln is a lot higher than an electric kiln. For a gas kiln in a situation like yours, I would suggest putting it outside. I have a small gas kiln in my backyard that I cover with a tarp between firings (no shed). The only drawback to using a tarp is that I have to wait for a couple of days with no rain forecast so I can fire it, unload it, and cover it back up before any rain. I can get to cone 10 in six hours and let it cool overnight. It is a converted electric kiln that can be found by searching for: TDI downdraft kiln conversion 

@ByrdIf the cone bent, then it reached that cone. The potential problem is that it didn't spend enough time at high heat to adequately burn out all the organic matter, which could cause issues with your glazes. If you're using a white clay body, then it'll probably be fine. If you're using a brown body then it's more likely to be an issue.
HERE is a thread with a lot of good information about firing Duncan kilns and how to slow them down. If you use the search bar you'll find several other Duncan threads that may be of use to you.

What temp did it reach after the initial 2 hours?
It will be interesting to see how your pots fared.

Babs
Zinc is processed two ways: the French process and the American process. The American process is just simply “roasting” (we call it calcining) that removes impurities. It is denser because it typically 80% pure, with 20% of various minerals commonly associated with zinc. The French process involves vaporing zinc at higher temps, resulting in a purity above 99%. It is finer, with less density. The zinc you are looking for is called Maximo 910 in the States, unless it has been sold to another company yet again.
Tom

Thought this was a good time (seeing it is American Thanksgiving), to put out a thank you to the potters on this forum who give selflessly of their knowledge and time to help other potters.  Together you have built a great resource and you are very much appreciated.  
 

per Standard Clay
 

I don’t think the low fire firing will change it dimensionally a bunch. Can you repeat it but make a generous gallery so it will fit a wider range of opening?

Looks like one man's collection of other folk's glazes, prob no text book as such
Some are Bwenard Leach's , some are Val Cushings , you say they are your professor's so why not ask him?

Looks like one man's collection of other folk's glazes, prob no text book as such
Some are Bwenard Leach's , some are Val Cushings , you say they are your professor's so why not ask him?

Looks like one man's collection of other folk's glazes, prob no text book as such
Some are Bwenard Leach's , some are Val Cushings , you say they are your professor's so why not ask him?