I have a very large kiln built out of 1 inch Fiberfrax blanket on the
inside, reinforced by 3 inch thick Fiberfrax block on the outside. I
also have a large soft firebrick kiln. There are differences in the
insulating qualities of these materials which you might consider when
deciding on the materials for your kiln.
Firebrick kilns take a relatively long time to heat up because you
must bring the volume of the brick up to your temperature. But the
material itself holds heat and continues to radiate it, even with the
element turned off. By contrast, ceramic fiber blanket does not itself
get hot, but acts as a “heat mirror”. (I’m told it was developed by
NASA to protect satellites from burning up upon reentry in to the
atmosphere.) Your kiln will initially heat up much more rapidly, but
will also lose its heat fairly quickly once the element is off,
especially if the door is momentarily opened.
Some comments about the durability of each material: someone else
suggested coating the blanket in the rigidizer solution to harden it.
Personally, I would not recommend doing this. The rigidizer breaks
down over time with heat, and becomes crumbly. I haven’t experienced
any significant deterioration of my (uncoated) ceramic fiber kiln.
However, it is constructed in a rather unique way, such that the
elements add support to the blanket. I’m also pretty careful with it.
There is another issue to consider with the blanket, however, in it’s
use in an enameling kiln. The stuff is virtually soluble in molten
glass. This means if enamel drips on the blanket, you will have a
hole which is difficult to repair. Brick is damaged by molten glass as
well, but not to the same extent, and can be repaired with firebrick
repair paste. The blanket does seem to be somewhat more fragile,
As far as fiber “dust” contaminating the glass, my large ceramic
fiber kiln is strictly a glass casting and fusing kiln, has blanket on
the inside of the lid, and I have never experienced any dust from the
fiber. It doesn’t seem to shed fibers. (The exterior hard block is
very dusty however, and I coated it with rigidizer.) However, I don’t
fire at enameling temperatures very often, nor am I opening and
closing the kiln as often as an enamelist does. At higher enameling
temperatures the blanket would tend to break down, and this could be a
problem in an enameling kiln. At some point you would probably need
to reline the interior of your kiln. This deterioration, combined with
the way the glass eats into the blanket when molten, would steer me
away from its use in an enameling kiln. I think as a burnout kiln,
where it is being used at consistently lower temperatures, it would
hold up just fine.
There are pros and cons to its use. Hope this helps a little.