Near Neighbor Glazes

cone 10 oxidation

Firing profile

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 2050 deg F

120 deg F an hour to 2250 deg F

60 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 deg F

Down Fire Profile

A half hour hold at 1750 deg F

A three hour hold at 1700 deg F

slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F

A one hour hold at 1650 deg F

The cones show this as a hot cone 10 firing.

Clay body is a grolleg porcelain from Tacoma Clay Art Center.

I show the glaze song-jian-1 and a variant song-jian_Z18

The glaze song-jian-1 is derived from a percentage analysis given by Nigel Wood in his book "Chinese Glazes"
in Table 58 of Chapter 7.

It is a low alkali metal, high alkaline earth glaze with high alumina and low silica.

The glazes song-jian-1 and song-jian-Z18 have nearly the same:

Total alkali metals, i.e. K2O + Na2O

Total alkaline earths, i.e. CaO + MgO

alumina.

They differ in the relative proportion of K2O and Na2O, and also in the relative proportion of CaO and MgO.

Song-jian_Z18 has slightly lower Silica, and higher Iron than song-jian-1.

The difference in appearance is profound, song-jian-1 is opaque and almost matte.

song-jian-Z18 is full gloss, and almost a transparent northern celedon with opaque mottled patterning.

As a first guess, I attribute the changed appearance of song-jian-Z18 to its higher Na2O, and lower K2O.

Neither the substitution of MgO for some of the CaO, nor slightly lower Silica seem as likely a cause of higher gloss and transparency.

Note that the crack in the second tile of song-jian-1 is not a dunting crack, it is filled with glaze, indicating that the crack formed
and opened while kiln was heating, so that the molten glaze was able to flow into the crack.

glaze composition of the glazes

Emperical Formula song-jian-1:

K2O        0.15
Na2O        0.01
CaO        0.63
MgO        0.21

Al2O3        0.83

SiO2        4.74
P2O5        .05
TiO2        .04

molecular percent Silica 69 %

Emperical Formula song-jian-Z18:

K2O        0.09
Na2O        0.08
CaO        0.54
MgO        0.29

Al2O3        0.84

SiO2        4.4
P2O5        .04
TiO2        .01

molecular percent Silica 68 %

The bowls is ~ 4 inches in diameter.

The glaze is shown on the inside and outside of the bowl, resp left and right

the two tiles are shown left and right

glaze song-jian-1

glaze song-jian-Z18