Spectrum glazes didn't fire correctly

[PS Muddy Waters]

Hello, looking for a little help and guidance. Logistics first though, to help you get the full picture. The clay body I am firing is the 4D Stoneware from Sheffield Pottery, and also their #63B White Stoneware Clay. Both according to Sheffield Pottery have a firing range of cone 02-6. I have just taken over a program and am working with a very old electric kiln, with gaps around the lid, which I know is causing  heat loss. My predecessor was firing the 4D stoneware clay body bisquing to 03 and glazing to 04. I purchased the Spectrum glazes to get by until I can finish testing my own batches of glazes. Several of the glazes did not produce much color and some not even close to the right color. Is this a temperature issue, or is this something else. For example the Oxblood Red 928 from Spectrum didn't leave anything behind but a clear sheen on one pot, and on another left a black and white mixture, very interesting and cool looking, but not the red color that was intended. The Midnight sky 920 and the Evening Shadow 901, both  fired very thin, even after the suggested 3 coats. Just wondering if anyone had any similar issues. And I also at this stage would love some recommendations for good low fire glazes that look close to higher fire reduction glazes. 

Many thanks for any and all help anyone can offer!

[Min]

Couple things about your claybodies, are you firing pots that will be for functional use or decorative pieces? If it's the latter then no worries but if the former then those pots will likely leak. Sheffield specs have the 4D Stoneware as a cone 6 body and the 63B as 02 - 6. At cone 6 the 63B probably will be tight enough with a posted absorption of 2.5% @ cone six and the 4D should be nice and tight with a posted absorption of 0.39%  By glaze firing to 04 the clay will be both weak and porous. Is the kiln you are using capable of going to cone 6?  

Re your glaze results,  I would make up some test tiles or even quick rough test pots and try different thickness of all your glazes plus try overlapping them with each other. Also, make sure they are really well stirred up before using them. 

Welcome to the forum! 

[PS Muddy Waters]

Hi Min,

Thank you so very much for your help and feed back! I don't think I can get this kiln up to cone 6. In theory it has the capability, but the lid has a pretty large gap. I have included a few pictures. I was assuming I would be able to fire to Cone 6 when I took over the program, and my predecessor originally said the kiln could fire that high, but then eventually said that they had never fired the kiln that high. What do you think? Worried I would never really reach Cone 6, or that it would take several days. 

[liambesaw]

You can lay a layer of ceramic fiber on the rim before you close the lid, and plug the peep holes, that might get you closer!

[Magnolia Mud Research]

If your testing shows that the kiln will not reliability achieve cone 6, I suggest that you lower your target just a little and fire the available low fire clay bodies to cone 3.  When I first started, the college studio fired a low fire commercial clay body to cone 3 oxidation.  All the ware was at zero water absorption and the studio glazes were fine.  There were also some engobes used that widened the glaze palette.  Glaze layering was also an effective technique along with commercial underglazes.  There was never any issue of the low fire clay body having excessive slumping, bloating, etc. due to over firing even though the clay was designed for cone 04 bisque and glost firing at cone 06.  (I currently use that clay body as a cone 10 dry matte glaze).   The clay body was chosen by his testing the available clay supply options.   

LT
 

[NancyAmores]

Oxblood 928 is a low fire glaze, so be sure not to fire any glazes meant for low fire (the whole Low Stone Series) to cone 6 or you'll have a mess of melted glaze. I liked the Amaco Artist's Choice glazes for low fire, they break nicely on red clay and are advertised as giving a 'reduction look'. Amaco Opalescents over underglaze is also very pretty, the raised texture stays the color of the underglaze, like a stained body or wash would do.

[Min]

It's normal to see a glow between the lid and body of the kiln like in your second picture but the gap in the first seems a bit wide. The lid hinge can be adjusted, have you tried that? When the kiln is cold does the lid fid the kiln without a gap? What is the kiln rated to go to? 

[neilestrick]

Is the gap due to the lid or due to the top row of bricks? Typically when I see a gap that big it's because the top row of brick have been damaged. Those bricks can be replaced. Even so, I doubt that gap is large enough to keep the kiln from reaching temp, assuming it's rated for cone 10, although it is a larger gap than normal. Take a look at the serial plate on your kiln and see what the max temp rating is. if it's rated for cone 10, it will get to cone 6 no problem assuming the elements are in good condition. What brand and model of kiln is it?

[PS Muddy Waters]

1 hour ago, neilestrick said:

Is the gap due to the lid or due to the top row of bricks? Typically when I see a gap that big it's because the top row of brick have been damaged. Those bricks can be replaced. Even so, I doubt that gap is large enough to keep the kiln from reaching temp, assuming it's rated for cone 10, although it is a larger gap than normal. Take a look at the serial plate on your kiln and see what the max temp rating is. if it's rated for cone 10, it will get to cone 6 no problem assuming the elements are in good condition. What brand and model of kiln is it?

Hi Neil,

I have attached a picture of the serial plate. This kiln was rebuilt years ago, that I know. The gap is mostly due to the metal frame around the side of the kiln lid. The bricks are in ok condition. It does say that my max temp is 2350, which means I could take it to cone 6. I do know that this kiln has never been fired that high, but the kiln was serviced in April of this year, and any elements needing to be replaced were. I have some cone 6 glazes ready to go, if you think the kiln can take it. 

Thanks again for the responses, to everyone, you have all been so helpful!!

 

[neilestrick]

Any issues with the metal band can be fixed by loosening the bands and moving them back into the correct alignment. You may have to remove any screws going through bands (handles, etc) to get them to move.

There's no reason that kiln won't go to cone 6 if everything is in good working order. I notice in one of your pictures that you don't have a thermocouple in the second down section. Did it come like that? Is there a thermocouple in the bottom section? I'm wondering if maybe this is old enough (serial number puts it at being built in 2000) that they only had 3 zone capability back then.

[PS Muddy Waters]

Hi Neil,

There is a third thermocouple just a little farther down. It's a pretty tall kiln. Makes it an interesting challenge for loading greenware.  Thank you again for all your responses! I am very excited to get a higher firing underway!