Newbie with LL Fuego Kiln - confused with outcomes

[Meredith Kathleen]

Hello,

I have a new L&L Fuego kiln, I did a test firing.  The kiln has standard settings for bisque and glaze, bisque is cone 04, glaze is cone 06 - I can programme it differently, but starting out with the their settings.

I  bisque fired some small vulcan black clay pieces using the glaze setting because I read that the clay required that temperature.  I was surprised with the colour, expected it to be more black.  

Then I glazed them with clear glaze, and two different celedon glazes and put them through a glaze fire again.  An electrician (annoyingly) shut off the kiln an hour into the the fire and I just restarted it fresh.

They came out this morning all powdery and I am not sure what I did wrong.

The kiln is brand new, it has a temperature reader and I checked and the temp did get high, I dont have cones in the kiln.

Thank you!

 

 

UPDATE - 

I defo didn't fire hot enough so refired at cone 6 - however, I should have maybe re glazed?
Also I used a ceyladon glaze and I think I need something much more opaque for the black clay....

LEARNING CURVE!!!

 

 

[Bill Kielb]

Maybe first thing to ask. Is the clay you are firing lowfire cone 04? Are your glazes lowfire as well?

[Hulk]

Hi Meredith!

Congrats on your new kiln.

The Vulcan black, does it require an 06 bisque and mature at cone 5/6? That's what I'm seeing here Vulcan Black Stoneware (Fine) 1200-1240C (potclays.co.uk)

Note, cone values begin (at the low end) 022, and ascend in temperature to cone 01, then continue to cone 13. Typical stoneware bisque is around cone 06 to 04, then glaze is cone 5 to 6. Take a long look at a chart, e.g. Celsius Cone Chart (clay-planet.com)

Black clays can be difficult! First, long slow bisque, with lots of oxygen is necessary to  burn off some/most of the gunk ("gunk" is rather unspecific, yes). I had better luck with black clay when bisque fire held ~20 mins at 750, ~30 mins at 1050, and almost an hour at 1500F. Careful glaze fire up to vitrification (but not too hot, to avoid bloating, and/or excess of fizzing/bubbling) using glazes that clear bubbles well and "heal" over as cooling begins were somewhat successful (I may not return to black clay - red, buff, speckly, white, cream - all in the running). Ample oxygen, again, is likely important here.

A powdery glaze may indicate that the firing wasn't hot enough to melt the glaze; if it looks powdery, but is in fact frothy, the effect may be due to aforementioned fizzing/bubbling.

A pyrometer (real time feedback) can be quite handy, and cones tell the true tale - compare your pyrometer reading notes(take and keep notes!) against your cones.

[neilestrick]

I'm wondering if you have confused cone 6 with 06. Cone 06 is about 998C, cone 6 is 1222C. Big difference. Double check the recommended cone for your clay and glaze, and make sure they're the same. If they're both supposed to be cone 6, then go ahead and re-fire them.

The cone 04 bisque is correct. We bisque low so that the pots are porous and will take glaze well. Then we glaze fire to whatever cone the clay and glaze mature at. The black color of your clay will not be achieved at bisque if it's a cone 6 clay.

[Tamas]

Hi Meredith,

 

I also have an L&L Fuego - I bought it pre-owned so mine is probably a few years older than yours but it is programmable. For cone 6 glaze firing I programmed it  according the schedule that was given in the user manual - it goes to 1185 Celsius with a slow climb during the last 100-150 degrees so it gives a nice cone 6 according to tests with witness cones.

And I also like to use Vulcan Black Smooth. It definitely comes out as a dark, almost black anthracite colour at that temperature (see the attached photo), which can  look a very dark brown under a clear glaze. I agree with Neil you may have accidentally underfired your pots.

I forgot to add: the Vulcan is a very tricky clay to glaze. Many glazes that look perfectly all right on white or buff clays come out totally different and unexpected looking on Vulcan. It is quite possible that there was nothing wrong with your firing but the glazes you used did not work well  on this clay. You will need to test and figure out which glazes work for you.