Stephani Stephenson on tue 5 may 09
A couple of other things about brick...
and this is from reading.... in no way am I a brickmaker, bricklayer, etc=
=3D
. but=3D20
i've always loved it, maybe it was the brick streets in the Kansas town w=
=3D
here my=3D20=3D20
grandparents lived. I loved those streets. And I loved all the brick in t=
=3D
he Colorado towns=3D20
where I grew up.
David Hamilton , in "Architectural Ceramics", makes a statement which lie=
=3D
s at the heart=3D20
of brickmaking,
"The value of the clay is not substantially increased by its conversion i=
=3D
nto bricks"
brick clays were needed in such quantities, they had to be suitable for =
=3D
use without any=3D20
additives, otherwise they were not economical to use. Typically the only =
=3D
modification to=3D20
the clay deposit was processing to reduce particle size. DIfferent clays=
=3D
from the same=3D20
seam could also be combined to improve performance, but usually the preci=
=3D
se mixing=3D20
proportions were very critical as to require stringent controls.
(Unfired brick such as adobe brick, often has straw, etc. added, and some=
=3D
fired brick has=3D20=3D20
inclusions of organic material which combust inside the brick itself, to=
=3D
increase firing=3D20
temperature in more primitive firing situations such as clamp firing. )
Most fired brick needs a flux of some sort though, and typically this was=
=3D
calcium, found=3D20
naturally in alluvial clays and seabed clays. Due to naturally occurring =
=3D
calcium , a hard=3D20
dense brick may be formed at a temperature of 1830 degrees F.
Calcium in larger particle size can present problems, the same kind of sp=
=3D
it out we=3D20
experience in pottery. HAmilton mentions that in brick, large particles o=
=3D
f iron in the form=3D20
of iron pyrite can also cause spit -out..with black slag like particles a=
=3D
t the base of the spit=3D20
out crater.
some of the yellow brick seen is due to the calcium bleaching the iron i=
=3D
n the clay.
Common brick are not vitrified and are fired below 1800 F
Hamilton says that engineering brick and paving brick is fired to the poi=
=3D
nt of vitrification=3D20
or to a point approaching this state under reduction conditions.=3D20
This makes sense to me. When we think of brick clays we think of iron bea=
=3D
ring clays.
even though "brick red" says "oxidation', i would think that some reducti=
=3D
on during the=3D20
cycle would be beneficial to take advantage of the fluxing action ofreduc=
=3D
ed iron, which=3D20
would get you a 'fused' body' at a lower, i.e. earthenware to low stonewa=
=3D
re range.=3D20
Perhaps alternating reduction oxidation , or perhaps flat out reduction.=
=3D
=3D20
because of the calcium present, these reduced bricks may still be a yello=
=3D
w to dark orange=3D20
color, rath rthan a brown or dull red.
The aim of firing these bricks is to get to maximum stregth and vitrifica=
=3D
tion without=3D20
incurring deformation.=3D20
again , this does not preclude openness in the body.
Hamilton also says engineering brick must have a 'porosity' of less than =
=3D
2%.
I don't quite know how to justify this with the 'less than 4.5% absorptio=
=3D
n' number from=3D20
the other source. it is so hard to tell of the language is just loose her=
=3D
e or if they are=3D20
referring to absorption and porosity the way Cushing refers to them....i.=
=3D
e. is tis apples to=3D20
apples or apples to oranges?.)
As an aside ,Hamilton also talks about large electric insulators, which m=
=3D
ust certainly=3D20
qualify as=3D20
"large outdoor sculptures".. there's a photo of them turning and jollyin=
=3D
g a large clay=3D20
insulator on a lathe... it is ,much larger than a person / He claims the =
=3D
insulator 'porcelain'=3D20
is fired to 1180 C /2150 F, glazed, and is non porous. ( and not easy t=
=3D
o work with for=3D20
typical forming methods)
the claybody he gives, if you are curious, is=3D20
ball clay 20-40 %
china clay 17-35%
quartz 20-50%
potash felspar 20-35%
A couple of thoughts relating to the discussion on architectural ceramics=
=3D
.
Cone 3 seems to be a standard reference in the temps used in traditional =
=3D
, what i think of=3D20
as late 19th century, early to mid 20th century terra cotta architectural=
=3D
ceramics.
but i think there is more variation out there than we know. it is difficu=
=3D
lt to know for sure=3D20
because=3D20
1. different clays were used in different regions , from different pits, =
=3D
and by different=3D20
companies for different purposes.
2. their methods of glazing , and their clay bodies were...guess what ? i=
=3D
ndustrial secrets!
I've read everything i could find with all kinds of glowing descriptions,=
=3D
etc. but little in the=3D20
way of actual formulas or information regarding clay or firing temperatur=
=3D
e, or firing=3D20
cycle. we know that Gladding mcBean worked and still works with Lincoln c=
=3D
lays. but that's=3D20
pretty general. Glaze formulas were kept locked up.=3D20
one example: and i don't have my notes so forgive me for forgetting names=
=3D
here. but=3D20
California China products was formed in National City, south of San Diego=
=3D
, because a=3D20
well trained prospecting ceramic engineer from great Britain found a whi=
=3D
te burning clay=3D20
deposit on=3D20
A nearby mountain, which he felt would equal the finest beleek procelain.=
=3D
so they hauled it out by mule, then built a railroad spur from the mounta=
=3D
in to the=3D20
harbour, where they built a factory. Turnse out the deposit was not quite=
=3D
as pure as the=3D20
initial projection, but it made a very good buff stoneware, which was tra=
=3D
demarked with=3D20
the name "kaospar". As far as i can figure they fired the kaospar to well=
=3D
over cone 10,=3D20
more like cone 13. and it was an excellent tile body.
the floor of the Sanrta Fe depot in San diego is made from it and it is b=
=3D
eautiful and my=3D20
guess is that the kaospar clay is in a number of California buildings..=
=3D
. Now CCPCO also=3D20
made the tile for Balboa park, and numberous fireplaces , etc. did they =
=3D
always fire this=3D20
high? I don't know. but i bet they had the capability... after all , high=
=3D
firing methods were=3D20
known in Europe, and most of the skill of that era came from=3D20
Europe, particularly England and Germany, and, especially with regard to =
=3D
the sculptors,=3D20
modellers, Italy. California also benefitted, in techniques, methods, an=
=3D
d skill, from the=3D20=3D20
middle eastern traditions, via spain, via Mexico.=3D20
SO , in this climate anyway, we have everything from cone 13 stoneware , =
=3D
to low fired=3D20
tiles to adobe...all functioning well.
which , again, different clays, different temps, different needs, differ=
=3D
ent approach.
I'm thinking about what vince said about the vitreous stoneware explodin=
=3D
g and I wonder=3D20
if that has also to do with a particular clay body and its inability to h=
=3D
andle thermal shock?=3D20
for example I had a High fire coffee mug which sheared and cracked right=
=3D
down the side=3D20
when hot water was poured in it .. but it doesn't mean that high fired wa=
=3D
re is unsuitable=3D20
for coffee mugs.
I agree with Dave in that cone 10 is usually great, fabulous, durable, an=
=3D
d strong for=3D20
outdoors.=3D20
Sometimes the argument is made by those who fire vessels which hold wat=
=3D
er, that you=3D20
NEED to have a non porous , no absorption, claybody for anything outdoor=
=3D
s.
Dave isn't saying this though, And I agree with Vince that the other ta=
=3D
ck is to take a clay=3D20
body which is more open, which is hopefully fired well enough so that par=
=3D
ticles are fused=3D20
and vitreous, but where pore space allows for migration of moisture, incl=
=3D
uding draining,=3D20
sloughing and re-evaporation , as well as expansion due to freezing...kee=
=3D
ping in mind=3D20
that minimizing the degree of 100% saturation is still a good idea...
A final bit I found interesting... in brick world there is such a thing a=
=3D
s 'frost inhibitor'=3D20
additives, which act somewhat like antifreeze, by lowering the freezing p=
=3D
oint of water in=3D20
the brick... they aren't recommended though because they actually cause =
=3D
moisture to be=3D20
retained in the brick, leading to prolonged dampness , which actually inc=
=3D
reased the rate=3D20
of weathering over time....
the more i think about it, the more I am amazed at the natural qualities =
=3D
of our chosen=3D20=3D20
and shared medium
P.S.
A few of us have posted Cushing's formula more than once to the list over=
=3D
the years.
no time to proofread, gotta go...sculpting today YAAAAYYYYYY!
Stephani Stephenson
Revival Tileworks
http://www.revivaltileworks.com
Stephani Stephenson on tue 5 may 09
maybe this didn't post, so i'll resend and try to shorten it a bit...
A lot of the following is and from reading.... in no way am I a brickmake=
=3D
r, bricklayer,=3D20
etc. but=3D20
i've always loved it, maybe it was the brick streets in the Kansas town w=
=3D
here my=3D20=3D20
grandparents lived or the brick in the Colorado towns where I grew up.
David Hamilton , in "Architectural Ceramics", makes a statement which lie=
=3D
s at the heart=3D20
of brickmaking,
"The value of the clay is not substantially increased by its conversion i=
=3D
nto bricks"
brick clays had to be suitable for use without additives, otherwise they=
=3D
were not=3D20
economical to use. Typically the only modification to the clay was proces=
=3D
sing to reduce=3D20
particle size. DIfferent clays from the same=3D20
seam could also be combined to improve performance, but usually the preci=
=3D
se mixing=3D20
proportions were NOT very critical as to require stringent controls.
(Unfired brick such as adobe brick, often has added organic material. Som=
=3D
e fired brick=3D20
has inclusions of organic material which combust inside the brick itsel=
=3D
f, to increase=3D20
firing temp in clamp firing, for exmple. )
Most fired brick needs a flux ,typically calcium, found in alluvial clay=
=3D
s and seabed clays.=3D20
Due to naturally occurring calcium , a hard dense brick may be formed at =
=3D
a temperature=3D20
of 1830 degrees F.
Calcium in larger particle size can present problems, the same kind of sp=
=3D
it out we=3D20
experience in pottery. Large particles of iron in the form can also cause=
=3D
spit -out..with=3D20
black slag like particles at the base of the crater.
Common brick are not vitrified and are fired below 1800 F
Hamilton says that engineering brick and paving brick is fired to a point=
=3D
approaching=3D20
vitrification under reducing conditions. aim: maximum strength without d=
=3D
eformation.
again , I don't think this precludes openness in the body.
This makes sense to me. When we think of brick clays we think of iron bea=
=3D
ring clays.
even though "brick red" says "oxidation', i would think that some reducti=
=3D
on during the=3D20
cycle would be beneficial to take advantage of the fluxing action of redu=
=3D
ced iron, which=3D20
would help produce a 'fused' body' at low to mid range temps.=3D20
Perhaps alternating reduction oxidation cycles in the firing.=3D20
because of the calcium present, these reduced bricks may a yellow to dar=
=3D
k orange=3D20
color, rath rthan a brown or dull red.
Hamilton also says engineering brick must have a 'porosity' of less than =
=3D
2%.
I don't quite know how to justify this with the 'less than 4.5% 'absorpt=
=3D
ion' number from=3D20
the other source. it is so hard to tell of the language is just loose her=
=3D
e or if they are=3D20
referring to absorption and porosity the way Cushing refers to them....i.=
=3D
e. is this apples=3D20
to apples or apples to oranges?.)
A couple of thoughts relating to the discussion on architectural ceramics=
=3D
.
Cone 3 seems to be a standard reference in the temps used in traditional =
=3D
, (what i think=3D20
of as late 19th century, early to mid 20th century European/U.S. terra c=
=3D
otta architectural=3D20
ceramics.
But i think there is more variation out there than we know.
Hard to track specific infoprmation because :
1. different clays were used in different regions , from different pits, =
=3D
and by different=3D20
companies for different purposes.
2. their methods of glazing , and their clay bodies were...guess what ? i=
=3D
ndustrial secrets!
Proprietary information!!!!!
3. access to the remaining/existing info
one example: and i don't have my notes so forgive me for forgetting names=
=3D
here. but=3D20
California China products was formed in National City, south of San Diego=
=3D
, because a=3D20
well trained prospecting ceramic engineer from great Britain found a whi=
=3D
te burning clay=3D20
deposit on a nearby mountain, which he felt would equal the finest beleek=
=3D
procelain.
so they hauled it out by mule, then built a railroad spur from the mounta=
=3D
in to the=3D20
harbour, where they built a factory. Turns out the deposit was not quite =
=3D
as pure as the=3D20
initial projection, but it made a very good buff stoneware, which was tra=
=3D
demarked with=3D20
the name "kaospar". As far as i can figure they fired the kaospar to well=
=3D
over cone 10,=3D20
more like cone 13. and it was an excellent tile body.
the floor of the Sanrta Fe depot in San Diego is made from it and it is b=
=3D
eautiful and my=3D20
guess is that the kaospar clay is in a number of California buildings...=
=3D
Now CCPCO also=3D20
made the tile for Balboa park, and numerous fireplaces , etc. did they a=
=3D
lways fire this=3D20
high? I don't know. but i bet they had the capability... after all , high=
=3D
firing methods were=3D20
known in Europe, and most of the skill of that era came from=3D20
Europe, particularly England and Germany, and, especially with regard to =
=3D
the sculptors,=3D20
modellers, Italy.=3D20
California also benefitted, in techniques, methods, and skill, from the=3D=
20=3D
=3D20
middle eastern traditions, via Spain , via Mexico.=3D20
SO , in this climate anyway, we have everything from cone 13 stoneware , =
=3D
to low fired=3D20
tiles to adobe...all functioning well.
which , again, different clays, different temps, different needs, differ=
=3D
ent approach.
I'm thinking about what Vince said about the vitreous stoneware explodin=
=3D
g and I wonder=3D20
if that has also to do with a particular clay body and its inability to h=
=3D
andle thermal shock?=3D20
for example I had a High fire coffee mug which sheared and cracked right=
=3D
down the side=3D20
when hot water was poured in it .. but it doesn't mean that high fired wa=
=3D
re is unsuitable=3D20
for coffee mugs.
I agree with Dave in that cone 10 is usually great, fabulous, durable, an=
=3D
d strong for=3D20
outdoors.=3D20
Sometimes the argument is made by those who fire vessels which hold wat=
=3D
er, that you=3D20
NEED to have a non porous , no absorption, claybody for anything outdoor=
=3D
s.
(Dave isn't saying this though),=3D20
And I agree with Vince that the other tack is to take a clay=3D20
body which is more open, which is hopefully fired well enough so that par=
=3D
ticles are fused=3D20
and vitreous, but where pore space allows for migration of moisture, incl=
=3D
uding draining,=3D20
sloughing and re-evaporation , as well as expansion due to freezing...kee=
=3D
ping in mind=3D20
that minimizing the degree of 100% saturation is still a good idea...
A final bit I found interesting... in brick world there is such a thing a=
=3D
s 'frost inhibitor'=3D20
additives, which act somewhat like antifreeze, by lowering the freezing p=
=3D
oint of water in=3D20
the brick... they aren't recommended though because they actually cause =
=3D
moisture to be=3D20
retained in the brick, leading to prolonged dampness , which actually inc=
=3D
reased the rate=3D20
of weathering over time....
P.S.
A few of us have posted Cushing's formula more than once to the list over=
=3D
the years.
Stephani Stephenson
Revival Tileworks
http://www.revivaltileworks.com
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