Decreasing Alkali Metals or Increasing Silca
A glaze and two modifications, either of which decrease pinholes.
Three glazes with nearly the same bases, i.e. first column oxides in their
empirical formulae. The second
The first glaze, longquan_iron_mashiko_Ip7, is a mottled black glaze with
metallic coppery crystals
The second glaze, longquan_iron_mashiko_Ip7_Malk, with lower alkali metals
than the first, has the same
The third glaze, longquan_iron_mashiko_Ip7_PSi, with higher silica than the
first, has an almost mirror-like
Both the glazes longquan_iron_mashiko_Ip7 and longquan_iron_mashiko_Ip7_MAlk
have a transparent rim,
Both decreasing alkali metals, and increasing silica could be expected to
decrease the viscosity
To muddy the waters, the second glaze, longquan_iron_mashiko_Ip7_PSi, contains
more Fe2O3 than the
bowl is ~ 4 inches in diameter.
bowl is ~ 4 inches in diameter.
bowl is ~ 4 inches in diameter.
150 deg F an hour to 250 deg F
400 deg F an hour to 1800 deg F
300 deg F an hour to 2050 deg F
120 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 deg F
300 deg F an hour to 1800 deg F then a 2 hr hold at 1800 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
50 deg F an hour to 1700 deg F then a three hour hold at 1700 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
K2O 0.09
Al2O3 0.71
SiO2 3.65
molecular percent Silica 66%
K2O 0.10
Al2O3 0.7
SiO2 3.64
molecular percent Silica 65.9%
K2O 0.09
Al2O3 0.71
SiO2 4.45
molecular percent Silica 69.5%
glaze has lower alkali metals than the
first, and the third higher silica than the first.
and a tantalizing luster. It is marred by dense
pinholes.
black matrix, but he metallic coppery
colored crystals are substantially larger, and it sports a dusting of
metallic
crystals. The pinholes are not entirely eliminated, though much
reduced in frequency.
glossy surface, and is mottled
brown and black. On the inside, with a moderate glaze thickness, the
pinholes are gone. There are some pinholes on the outside, perhaps because the
glaze coating is nearly twice the thickness of the inside.
indicating a degree of fluidity not present in the
glaze longquan_iron_mashiko_Ip7_PSi.
of a glaze, which often increases pinholes. In this
glaze the result was fewer pinholes
other two glazes. Fe2O3 increases viscosity in a
glaze and may have counteracted the reduction in alkali metals.
Image of the glaze longquan_iron_mashiko_Ip7
inside
outside
Image of the glaze longquan_iron_mashiko_Ip7_MAlk
inside
outside
Image of the glaze longquan_iron_mashiko_Ip7_PSi
inside
outside
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula longquan_iron_mashiko_Ip7 :
Na2O 0.43
Li2O 0.19
CaO 0.13
MgO 0.16
Fe2O3 0.14
P2O5 0.03
Empirical Formula longquan_iron_mashiko_Ip7_MAlk :
Na2O 0.38
Li2O 0.16
CaO 0.20
MgO 0.16
Fe2O3 0.15
P2O5 0.02
Empirical Formula longquan_iron_mashiko_Ip7_PSi :
Na2O 0.43
Li2O 0.18
CaO 0.14
MgO 0.16
Fe2O3 0.20
P2O5 0.03