Firing Methods and Results
Salt Glazing & Wood Firing
on kilns can be found in
Kiln Design Tips
Problems & Solutions
Kiln & Kiln Furniture when Salt Glazing
The process of salt glazing is hard on a potter's
kiln, the posts and kiln shelves used in the salt firing.
Salt glazing shortens the life span of a kiln. A salt kiln may
only last 1/5 as
long, as a kiln in which sodium is not used.
Potters who use only a small amount of sodium or salt will
experience a far lesser degree of deterioration to their kilns. Robert
chooses to use a larger concentration of sodium when firing, to achieve
the fluid salt glazes he seeks. He pays the price for that glaze look in
the extra maintenance needed to keep his kilns in good repair.
Kiln Shelf Before Cleaning
Kiln Shelf After Cleaning
Sodium Vapor reacts with Silica (a component of the shelf).
The shelf literally dissolves, creating glass bubbles. Orange
halo's, result from flame flashing, and a few wads from the underside of
pots (white) have fused to the surface.
Kiln shelves are ground smooth, using a diamond cup grinder, to remove
the glass buildup, and wadding, from the previous firing. A light wash
of Alumina Hydrate and Kaolin is used to coat the shelve to improve
resistance to the sodium vapors.
Maintenance of Salt Kilns
When choosing to salt glaze, much time is required to care
for the kiln and kiln furniture. This time is
not obvious to customers or potters who are unfamiliar with the
technique. It takes Robert about 18 hours to do maintenance on his wood-salt
kiln after each firing. Most of that time is cleaning salt and ash glaze
build up from the floors, bag walls, and the one hundred Kiln Shelves
used in his large Noborigama.
Salt Glazing -
The Diamond Cup, which costs about $85, is worn out after cleaning
the furniture from one large kiln firing. The clean up after each firing
also consumes one of the "Wire Rope Brush Cup's" which cost about $45
Above photo shows: Kiln Shelf before Grinding
Maintenance of Salt Kilns
Kiln Shelf Resurfacing
The Diamond Cup is shown on this Grinder, it is a
grand tool for removing hard salt glaze buildup. Another attachment,
Rope Brush Cup" , visible in the bottom middle photo at
right, works faster on light corrosion
It is necessary to wear a Dust Mask, Gloves and Face Shield
An Angle Grinder is an excellent tool for removing salt
glazed kiln wash and other corroded surfaces. The "Segmented
Diamond Cup" used on this grinder is best for hard to remove
| Mask, Gloves, Face Shield, Diamond Cup
Grinder (twisted metal brush attachment) Photo shows these tools sitting on cleaned and rewashed
= More Time
Robert glues wads to pots in the wood and salt chambers of his
Noborigama. This large kiln consumes 1500 pots, and each piece
will require between 3 to 8 wads. Over 6000 wads are made and
glued to his pots when loading, adding nearly a day of work just to do
all the wadding.
Wash & Wadding =
To re-wash the kiln shelves, floor, and caps of the bag walls, consumes
about 8 Gallons of Kilns Wash, and 50 lbs of wadding in each firing of
Robert's large Noborigama.
These serving bowls were separated by wadding
in what is known as tumble stacking,
A problem can occur when glaze runs off the top pot fusing the wadding
to both pieces.
The small urn (left) was sitting on a shelf next to the mug.
A slight shift in the stack of shelves, brought it into contact with the mug.
though neither pot had glaze on the outside,
the sodium vapors created a salt glaze, that fused them together.
|Bowl within a Bowl
This small bowl was displaced from its
shelf and fell into the larger bowl. The potter, who helped stoke
Robert's kiln, inadvertently hit the bowl with wood, when stoking
the fire box.
Every wood and salt firing is bound to have a few mishaps, but they
can be kept to a minimum when the kiln is stacked with care.
The two bowls "kissed" in the firing
when a post supporting the kiln shelf shifted slightly during firing.
If you fire enough pots, accidents are bound to happen. The glaze fused
the bowls together, breaking them apart,
destroyed both pieces.
The wadding on the Pilgrim Flask (middle of photo) shifted in the
resulting in the pot "kissing" the adjacent kiln shelf.
It is important to apply a solid base of wadding, to prevent this kind of mishap.
The number, size and placement of wadding, will make the difference
between success and failure.
The wadding supporting the Light Blue
"Pilgrim Pot" on the left
settled during firing, tipping it slightly and fusing it to the red