Bisque surprises, Egyptian Paste and Burnt Lawns
This weekend we did a bisque firing of most of the clay pieces that we'd made over the winter with our molds.
Above are the pieces, pre-firing. Most were clay, but there were four Egyptian paste objects.
Ka-blam! All the miniatures of the Hall blew up very early on, around 100°. I figure the clay was too thick, pockets of air within expanded... But the Venuses and yoni-lingams turned out lovely.
And as usual, even if we thought this firing was going to be very straightforward, there were strange surprises. Three pieces had been modelled with the clay/sand mixture with which we built the mud oven: a yoni-lingam, a pine cone and a Venus.
For some reason, the Venus got an incredible shiny glaze on it. There are tiny traces of shine on the yoni-lingam and pine cone, but the Venus shines nearly all over.
I'm guessing it's because of the sand that was added, extra silica getting glassy at high temperatures. But why her and not the others? Did the chance flickering of the flames within the kiln brush her just right? Now we'll have to experiment to see if we can replicate the effect next time.
More questions: the Egyptian paste objects both worked and didn't work. To make the paste, over the winter we made up more homemade copper carbonate:
Here's Jorge in February grinding up some silica to add to the feldspar and clay powder.
Like the first time we tried it, the paste turned out very sticky and difficult to model:
We filled one large Hall mold and two small molds.
The Venus and pine cone (and cube) came out pretty well - a nice blue.
The Hall (visible at rear in the photo above) didn't turn blue on top, but turning it over, it's an incredible lustrous, glassy blue:
(It got a bit stuck to the firebrick.) The question is why did it get so wonderfully blue on the bottom, against the brick? Was it hotter there? If we put these pieces in again and fire the kiln hotter, will they all go glassy-blue like this? To be determined...
We got the kiln up to a max of 1050° but in fact I'm skeptical of the readings throughout and think that we may need a new thermocouple (we might have wrecked it with this experiment). At various points the reading would seem to get a bit stuck and then with the slightest movement of the probe, the temperature would jump 100° or so, and then sometimes proceed from there or else drop back down. The paste needed at least 950°, but how high we really got (and how quickly we ramped up) is not clear. Maybe that's why those pieces broke at the low temperature of 100°? Maybe it was in fact already much hotter.
It got hot, to be sure. The glass platform I used to protect the lawn below the firebrick and ceramic fibre cracked (as I suspected it might), but as I was cleaning everything up the reflection in the glass reminded me of the Milky Way...
After a great day of the Craft, there's nothing like looking into the Milky Way and dreaming of billions of giant suns exploding at impossible temperatures, all at impossible distances high above your head, all with the smell of burnt lawn in your nose.
Next up: glazing, oxides, tinder fungus, and molds for casting pewter.
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| (From right to left, a few hundred thousand years of pyrotechnic progress.) |
Above are the pieces, pre-firing. Most were clay, but there were four Egyptian paste objects.
And as usual, even if we thought this firing was going to be very straightforward, there were strange surprises. Three pieces had been modelled with the clay/sand mixture with which we built the mud oven: a yoni-lingam, a pine cone and a Venus.
For some reason, the Venus got an incredible shiny glaze on it. There are tiny traces of shine on the yoni-lingam and pine cone, but the Venus shines nearly all over.
I'm guessing it's because of the sand that was added, extra silica getting glassy at high temperatures. But why her and not the others? Did the chance flickering of the flames within the kiln brush her just right? Now we'll have to experiment to see if we can replicate the effect next time.
More questions: the Egyptian paste objects both worked and didn't work. To make the paste, over the winter we made up more homemade copper carbonate:
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 |
 |
 |
Here's Jorge in February grinding up some silica to add to the feldspar and clay powder.
Like the first time we tried it, the paste turned out very sticky and difficult to model:
The Venus and pine cone (and cube) came out pretty well - a nice blue.
The Hall (visible at rear in the photo above) didn't turn blue on top, but turning it over, it's an incredible lustrous, glassy blue:
(It got a bit stuck to the firebrick.) The question is why did it get so wonderfully blue on the bottom, against the brick? Was it hotter there? If we put these pieces in again and fire the kiln hotter, will they all go glassy-blue like this? To be determined...
We got the kiln up to a max of 1050° but in fact I'm skeptical of the readings throughout and think that we may need a new thermocouple (we might have wrecked it with this experiment). At various points the reading would seem to get a bit stuck and then with the slightest movement of the probe, the temperature would jump 100° or so, and then sometimes proceed from there or else drop back down. The paste needed at least 950°, but how high we really got (and how quickly we ramped up) is not clear. Maybe that's why those pieces broke at the low temperature of 100°? Maybe it was in fact already much hotter.
It got hot, to be sure. The glass platform I used to protect the lawn below the firebrick and ceramic fibre cracked (as I suspected it might), but as I was cleaning everything up the reflection in the glass reminded me of the Milky Way...
After a great day of the Craft, there's nothing like looking into the Milky Way and dreaming of billions of giant suns exploding at impossible temperatures, all at impossible distances high above your head, all with the smell of burnt lawn in your nose.
Next up: glazing, oxides, tinder fungus, and molds for casting pewter.
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