Why Whiting Works

[Pamela Theis]

I asked Richard Burkett to explain to me a technical explanation for why/how
whiting functions when added to the salt/soda mixture. This was his response:

Whiting when heated high enough (I can get the exact temp) turns into
calcium oxide (losing CO2) which is really quite refractory (again I
can get the melting point later) IF there's no handy silica or other
material around with which it will form a eutectic. Sodium doesn't do
it, so the sodium (soda ash, soda bicarb) evaporates forming the glaze
while the calcium oxide just sits there waiting to be swept out of the
kiln later. Calcium oxide is not that stable around moisture, so it
will gradually absorb water from the air.

I found this interesting and thought I would share it with everyone.
Pamela

[Deborah Woods]

I'm not sure I understand the importance of it then in the mix. If it's refractory and remains in the bottom of the kiln or firebox, then what is it's purpose? Is it just a vehicle to help distribute the soda? What happens if you don't use it?
Debbie

[Pamela Theis]

The fact that it is refractory is the point so that you can sweep it out, rather than salt/soda alone will glaze and shorten the life span of the bricks. You don't have to use it. We don't here in Baltimore, or anywhere else that I have fired actually. It is vehicle that distributes, but mainly protects the brick.
Pamela

[Deborah Woods]

Alright, not to beat a dead horse here, but trying to fully understand this. So, if it's purpose is to help protect the brick and shelves presumably, is there a possibility that it could interfere with getting good soda accumulation on the pots themselves? Michael mentioned the whiting dropping to the firebox floor in a wood kiln, but if you are spraying directly into a kiln through ports then it's more immediately inside the kiln.

[Keith Phillips]

I think it's a matter of the surface you want your pots to have. Spraying seems to modify the draft path through the kiln, getting soda evenly throughout. One thing I've noticed using the whiting mixture, is the "directional" nature of the soda deposits. Dumping in the fire box seems to make the soda take the natural draft path through the kiln getting better flashing and variation on the surface of the pot rather than even coverage.

[Emily Murphy]

I think you're spot on with this description. I'd add the spraying actually gives a "wetter" surface. And pots fired with the dry mix tend to have a feeling of a wood firing because of the strong directionality of the soda flashing.

[Emily Murphy]

It has a couple of purposes: *to protect the firebox from the soda, *to make it easier for the soda to get cleaned out of the fire box, *and basically to keep the soda from sticking to itself and just sort of fizzling out. The soda is much more active with the whiting added. The difference can be pretty amazing. The soda movement/ coverage is much better.

[Michael Kline]

What is the ratio of soda to whiting? I wonder, in a wood kiln, whether the whiting would be carried to the pots instead of dropping to firebox floor?

[bryce brisco]

What about the flashing effects? Sea shells have fairly pronounced localized flashing when used as wadding, when they burn out they become calcium carbonate. So in effect, wouldn't adding whiting to your salt/soda mix heighten the flashing throughout the kiln in the same way?

[Michael Kline]

I wonder about that. Is the flashing from the calcium or the salt in the shell. I would guess from the shell. Hmmm.

[Deborah Woods]

This is interesting. I wonder if it is the case that whiting can cause flashing, then it could be interesting to mix some with wax or I suppose just water and use brushwork with this mix directly on the pots.
Ditto Hmmm.

[Emily Murphy]

The flashing is from the salt in the shells. If you ever use a shell that has, for instance, been bought from a craft store, it won't flash because it has been washed. I suspect if you brush whiting directly onto your pot you'll just get a white powder.

[Emily Murphy]

I switched from a no-whiting mixture to a with whiting mixture 6 or 7 yrs ago and I wouldn't go back to firing soda without.
-I have seen it help distribute the soda better in firings. I use a chunky wood chip - soda - whiting - water mix. After adding a round of soda with whiting, the soda is active for a longer period of time than without. Better distribution, less soda needed.

-It does an amazing job protecting the firebox. In previous kilns that were fired without the whiting, the soda pool up on the floor of the firebox and EATS into the floor brick. With the whiting, the mixture that is left in the firebox is chunky. If you leave it for a couple of days it will turn to "dust" and can be swept out. To speed up this process, you can splash some water over the chunky mixture and it will turn to "dust" at a much faster rate. I like to keep the firebox very clean, so it's cleaned well, and then actually dusted with whiting before the next firing. You'll have to do some chipping and clean up, but it's fraction of what it used to be, and it doesn't eat into the brick like the soda only mix.

-The amount of whiting that I use is 1 part (by weight) whiting to 1 part soda. I use 2.25 lbs. soda ash, 3 lbs. soda bicarb and 5.25 lbs of whiting. Mixed with wood chips and then cold water. Mix immediately before use.

-Emily