Steve Slatin on wed 14 mar 12
Birdie --=3DA0There are several possibilities.=3DA0 All the ones I=3D0Acan =
think =3D
of will require more testing to deal with.=3D0A=3DA0=3D0AI'd recommend firs=
t=3DA0ch=3D
ecking the cracking carefully -- crazing =3D0Aand dunting don't 'feel' the =
sa=3D
me.=3DA0 The sharp feeling that running a =3D0Afingernail over a dunted pie=
ce i=3D
sn't like the rather smooth=3D0Afeel of crazed glaze.=3DA0 Maybe you need t=
o go=3D
in the other=3D0Adirection, and increase the CTE of that glaze.=3D0A=3DA0I=
f it r=3D
eally is crazing, maybe the problem is the new clays.=3DA0 (Try a few more.=
)=3D
=3D0A=3DA0=3D0AIf not, maybe you mis-measured the glaze when mixing it.=3DA=
0 This=3D
=3D0Ahappens.=3DA0 (Try again.)=3D0A=3DA0=3D0AOr maybe you measured properl=
y, but use=3D
d a new bag of whatever ...=3D0Aand it was wildly out of spec.=3DA0 Or mism=
arke=3D
d (this happens=3D0Amore than you'd think).=3DA0 Check things over, and if =
anyt=3D
hing=3D0Adoesn't look as it should, replace it and try again.=3D0A=3DA0=3D0=
AI'm sur=3D
e there are other possibilities I haven't thought=3D0Aof.=3DA0 One way or a=
noth=3D
er, though, you can fix it.=3DA0 And you will.=3D0A=3DA0=3D0A=3DA0=3D0AStev=
e Slatin -- =3D
=3D0A=3D0A=3D0AN48.0886450=3D0AW123.1420482 =3D0A=3D0A=3D0A----- Original M=
essage -----=3D
=3D0AFrom: Birdie Boone =3D0ATo: Clayart@LSV.CERAMIC=
S.OR=3D
G=3D0ACc: =3D0ASent: Wednesday, March 14, 2012 1:39 PM=3D0ASubject: i know =
my gla=3D
ze but something is WRONG!=3D0A=3D0Ahi!=3D0Aneed help FAST! here's the scen=
ario:
Birdie Boone on wed 14 mar 12
hi!
need help FAST! here's the scenario:
i use the following base glaze: insight software says COE is 6.2, Al:Si i=
=3D
s 8
20 F 3134
20 dolomite
20 spodumene
20 om4
20 flint
i also use the following bisque slip: insight software says COE is 5.7, A=
=3D
l:Si is=3D20
4.3
10 custer
16.8 om4
19 glomax
16.8 grolleg
19 flint
4.7 borax
4.7 zircopax
i have successfully used this slip and glaze combination on 'm390' plains=
=3D
man=3D20
clays while living in montana and on 'earthen red' from highwater clays w=
=3D
hile=3D20
living in virginia.=3D20
NOW, i am in santa fe, nm, using the same combination; i tried it on lagu=
=3D
na=3D20
clays 'SB red' and it crazed horribly. i tried it on sandia red from new =
=3D
mexico=3D20
clay and it crazed horribly as soon as i unloaded it (below 100 deg F).
shrinkage rate for montana clay, nc clay and new mexico clay's 'sandia re=
=3D
d'=3D20
are all the same. laguna's 'SB red' significantly lower (so the crazing m=
=3D
ade=3D20
sense).
tried different firing schedules, different peak temps, nothing changes.
glaze is not too thickly applied.
pot's perfect sitting on kiln shelf, i take it out and it begins to craze=
=3D
crazing on the inside first, then more on the inside than on outside (som=
=3D
e not=3D20
at all on the outside or just one or two small lines)
craze lines on wall are horizontal-does this mean anything?
bottom of pot unglazed (kind of a wide surface to be glazed only on one s=
=3D
ide,=3D20
BUT NOT A PROBLEM IN THE PAST) and crazing begins here-am i being=3D20
stubborn to think this is not the cause of the crazing?
what am i missing here and how can i make a quick fix?
i thought that adding a low expansion material to the glaze should help w=
=3D
ith=3D20
fit? i did this in insight software and the COE went UP! am i looking at =
=3D
the=3D20
wrong thing?
is it dunting? the clay is not cracking, just the glaze.
OH, PLEASE HELP! THANKS!!
-BIRDIE
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