mel jacobson on sun 10 jul 11
there is a great deal of confusion about
how to reduce your kiln, what happens and how much
is too much.
i have spent a lifetime looking at thousands of firings
in reduction kilns.
some thoughts:
most over do. they reduce too hard, to much
and don't have a clue what is going on.
kiln shelves too big and stuck side by side.
this is a sure way to get poor total reduction in your kiln.
far too many pots in the kiln. another sure fire way
to have poor total reduction.
bag walls stuffed in the kiln for no reason. some have
no idea the function of a bag wall. in a gas kiln, what
are you protecting your pots from? heat, reduction. wood kilns
and other fuel kilns become a new story. then the bag wall
has a function.
the science of carbon, and monoxide is interesting conversation,
but it does not solve any problems in how to reduce your kiln
properly.
one of the most critical parts of our new kiln book is the
section on firing for `ecology`.
kilns should be fired in the most efficient way possible. we are going
to use fuel to fire, so do it with max oxygen. get as much heat
btu's as you can from your burners. the burners never produce
reduction...your kiln produces reduction.
the damper is your best friend. how to control it takes time
and effort and charting.
there are several elements that are needed to produce reduction.
gas pressure
damper
and lack of oxygen (primary air).
if you over pressure your kiln, flame will come from
every opening. reduction happens,.
is it good reduction, safe and ecological? no.
if you reduce the primary air in your burner and the flame
become yellow your kiln will go into modest reduction.
is it good reduction, safe and ecological? no.
so, that leads us to a very important concept.
fire for blue, clean flame. get as much heat as you can
into your kiln. use the damper to control back pressure, and
in most cases about three inches of flame from your primary
peep will be fine.
start your kiln on max heat/gas pressure. as the kiln builds energy
you can back off on the gas pressure. in most cases you will need
far less fuel as the kiln nears cone 9.
so, reduce pressure, and slowly slide your damper in to maintain
the three inch back pressure.
never let your kiln stall. adjust pressure and damper so the kiln
continues to rise in heat. often too much pressure is the primary
cause of stalls. it is a sin. you are not driving a car. pushing
the gas pedal does not make your kiln fire faster. proper energy
levels building in a steady way is best.
you will be able to read your pots after you open the kiln.
the color of the clay tells the story and of course you will
probably have waves of color that will tell you the pot was not
reduced properly.
chart that reduction current in your kiln. see and understand
why some pots or shelves did not reduce. often they are
the same places...over and over. in fact, that may be a place
to fire iron red, not copper red.
the easiest way to fire for reduction is firing a variety of
sized pots. open the kiln shelf plan...get a shelf of tall pieces
near the middle. that is why sets of dishes are such a pain to
fire...far too many shelves all packed into the kiln.
no room for the gases and carbon to move around.
they are called heat traps. sort of like dams in the kiln
that block the flow of energy. some do it every firing...
don't have a clue.
the potter has to change things around...try different stacking plans,
then chart the results. see what works best. then repeat it for
effect. chart that again.
i even leave a shelf free of pots to see how it affects
the reduction pattern.
this idea of stuffing kilns is totally backwards. far too
many pots become seconds and have to be thrown away.
why fire them for loss? god, leave them out for the next
firing, and get all racers.
loss is the ecological disaster in a kiln. no using fuel.
loss....fire for 100 percent racers. you will be one
happy potter.
i/we fire a lot of sticks and wood in our kilns at home
and at the farm. when the kiln is done we close it up
let the heat drop of bit then add small 1x1x12 branches, sticks
burnables. in fact we burn straw, garbage, wood scrap etc.
we know that kilns reduce on the way down. just do...and
don't tell me they don't. we have fired dozens of kilns
at the farm with fast fire in oxy, then reduce on the way
down with wood scrap...perfect shino, copper red. it works.
we like to fill the kiln with soft carbon/monoxide for several hours
on the way down. you need good ventilation...and fans. but we
assume you have that already. if you don't, you should not be
reducing your kiln anyway. many of us think david shaner died
of manganese poison...as his kiln was inside his studio.
who knows...but, it was not good. those neurological diseases
are hard to diagnose.
oxyprobes are nice tools, but very expensive, and hard to
keep in working order for years....they just break down.
so, i don't need them any longer.
they are the jaguar of ceramic tools...they spend more time
in the shop than they do working for you.
charting your kilns firing patterns will teach you more than
any other tool. and, every firing is different.
stacking, weather, and the list goes on.
mel
and there is no better stack than a 12 inch straight as
an arrow 12 foot stack. your flue size will be very
important...and most make that size twice as big as needed.
read nils book. he is dead on right.
(spiral pipe/with flue liners...itc. )
from: minnetonka, mn
website: http://www.visi.com/~melpots/
clayart link: http://www.visi.com/~melpots/clayart.html
new book: http://www.21stcenturykilns.com
alternate: melpots7575@gmail.com
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