: timbo_heff - Viewing Profile

"how much ash/glaze deposit was on shelf before? did you see shelves before firing?
how do the top of shelves look?
are shelves used one side up only?
have shelves been used in soda/salt firings?
was it all shelves or just a few?"

They are definitely old shelves: been fired many many times never in salt or soda: just lots of hot wood fires. These could be 20 years old or even more.
They were scraped pretty well: maybe not perfectly clean but not covered with old ash at all.
It was just these 1" ones that it happened to: the skinnier ones did not bubble and foam.

Schedule:
Candled for about 10 hours staying below 200F.
Then went 75 - 100 /hour til 06 down.
Then an hour or 2 of heavier reduction.
Then up to 2100F on the pyrometer for 30 hours until 11/12 down in front 9/10 in back:
Another heavy reduction cycle for a couple/ few hours.
held another 12 hours around 2150 on pyro.
Then we gently stuffed the kiln with big fat chunks to make some charcoal / charwood and sealed it up to hopefully get some slow reduction cooling.
Took about 4 days to get cool enough to open.

Here's something strange that happened: a couple of big thick (1") shelves seem to have fluxed and melted. They bubbled and foamed and dripped onto pots below. The "glaze" they made luckily looks pretty cool: blue and black, super glassy and deep. The one pictured was right up front but it happened further back as well.
Anyone ever have this happen?
 shelves.jpg (1.03MB)
Number of downloads: 31

 wf13-2.jpg (814.6K)
Number of downloads: 53Super fantastic fire! 400 pots, 95% good. Great diversity... 14 potters in kiln. About 4 days, about 4 cords. Reduction phases around 08 and again at top temp. ^10/12 front stack, ^9/10 back.
Here are a few of mine: some unglazed, some shino.  wf13-1.jpg (771.3K)
Number of downloads: 58

Shelf paper is for glass firing:
Best practice for kiln wash is 3 fired on coats per below;
The prob with the stuff is that you can't flip your shelves which will extend their life. I think better to dry foot, use stilts, and or when you throw the foot area of your pots : leave a little glaze catching edge (but not always practical or aesthetically correct)
Here is best practice though:

DIRECTIONS FOR USE
Kiln wash is applied to kiln shelves to protect them from glaze drips. On a washed shelf, drips can be easily removed without gouging or marring the kiln shelf.
Mix the kiln wash with water to a thin cream consistency. Apply only one coat at a time. Use a wide paintbrush or utility brush (a 2" - 3" wide, soft bristle brush generally works best). Three individually firedon coats of kiln wash are preferable.

APPLYING KILN WASH
1) Make sure the floor of the kiln and the tops of the shelves are coated with kiln wash. This will protect these surfaces from melting glaze and ceramics.
2) Do not coat the bottom or sides of the shelves.
3) Do not apply kiln wash to the brick sides or element holders.
4) Apply the kiln wash to the thickness of a post card.
5) The only purpose of kiln wash is to prevent any glaze that drips from a piece from sticking to the floor or shelves. This saves both the piece and the floor or shelves. If dripping should occur, simply remove dripping and cover the spot with new kiln wash.
6) When you are applying kiln wash to your shelves for the first time, it helps to dampen the top of your shelves with a wet sponge or a water-filled spray bottle first. This makes the kiln wash go on easier and more evenly.
7) For the kiln wash to really protect the kiln shelves it is best to apply three separate coats. In addition it is best to fire each coating separately. (If you brush one coat on, let it dry and then brush on another, you could actually be brushing off the first in the process, so ideally each coat should be fired on). The shelf can be used while firing the kiln wash on, so theoretically you would put one coat on, load the shelves and do your test firing of the kiln. The second coat would be fired on in the first bisque and the third coat in the second bisque or first glaze (whichever comes next). Fire at least to cone 018 - hot enough to give the kiln wash enough adherence to the shelf to prevent it from coming off in the second coating. Note that some people
get away fine without three firings of the kiln wash. However, we include this recommendation as a “best practice”.
8) If you notice that your kiln wash is flaking off, use a paint scraper (or something similar) to remove any loose bits, then reapply kiln wash. If glaze drips ontoyour shelf, use the paint scraper to pop the glaze drip off and clean up any loose areas around the area, then dab some more kiln wash in the bare area.

PROGRAM TO QUICKLY DRY KILN WASH
Here is a program that will dry the kiln wash in a hurry:
In the Vary-Fire section:
Press Enter Prog, Press '1'
Press Enter, Press '1'
Press Enter, Press '60'
Press Enter, Press '200'
Press Enter, Press '600' (for 6 hours, 400 for 4 hours, 800
for 8 hours etc of hold time at 200 degrees)
Press Enter, Press 9999
Press Enter, Press START

I agree with Baymore: try addressing the bisque firing:
Do a "slow" bisque and a a one or two hour hold just below the point of sintering: (say around 1550 F)
this gives all the junk a chance to burn out before the clay skins over and traps the gasses that cause bloats.

This schedule prevents these problems even in the most troubled clay bodies.