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Re: [teacherartexchange] reglazing mugs (kiln vapors)


From: Holmgren (holmgren_at_TeacherArtExchange)
Date: Sun Mar 18 2007 - 18:08:48 PDT

Thanks for the info, Marvin.

Mary H.

----- Original Message -----
From: "Marvin Bartel" <>
To: "TeacherArtExchange Discussion Group"
Sent: Saturday, March 17, 2007 12:25 PM
Subject: Re: [teacherartexchange] reglazing mugs (kiln vapors)

> Mary H. wrote:
>>Reading about glazing and fumes--is it normal to have some fumes--bad
>>smelling--when doing a glaze firing? I was firing a load of clay bowls
>>that were glazed with concept underglazes--at cone 05. I have a Skutt
>>kiln with the envirovent system. The smell was really bad. ???
> Mary H.
> I stand corrected. Not all firing odors are toxic. I was referring to
> aromatic hydrocarbons used as organic solvents (in china paints and
> lusters). Some other chemicals can also produce toxic vapors - some
> without any noticeable odor. I think the companies that sell school
> supplies are careful not to use hazardous materials (or at least include
> warnings if they do), but we need be vigilant. I am not familiar with
> "concept" underglaze and could not say if the underglaze you used has
> anything that is both volatile and toxic in it. Perhaps you should ask
> the company that sells the product to tell you the source of the firing
> odor. Tell them at what firing temperature the odor is worst, and try to
> describe nature of the smell. Also be sure you do not get the same smell
> from the clay without the underglaze on it. Many clay bodies contain
> enough sulphur to make a significant haze in the room toward the end of
> the firing if not well exhausted. You can even taste it. This
> may not be as harmful as some fumes, but I certainly would not want to
> breath much of it. I have seen glass window panes above kilns that are
> etched by the kiln acid fumes so badly that they could be used for
> bathroom privacy glass.
> The envirovent systems and other vent systems need to be routinely checked
> before and during each firing and repaired if any odors are noticed.
> 1. Look and be sure the openings are not clogged where the system draws
> fumes from the kiln. Have a piece of coat hanger wire handy to check
> before loading the kiln to see that the hole(s) is (are) open in the kiln
> bottom.
> 2. Be sure the lid and the kiln seams are nice and snug. If you see gaps
> on an old kiln, seal it with some kiln fiber insulation or at least stuff
> some clay in the openings. You make wadding with clay and sand that can
> be used to seal a hot kiln.
> 3. Be sure peep holes and thermocouple holes are tightly stoppered. Check
> under the kiln during firing to see if it is sealed tight against the kiln
> when the kiln is hot. Heat warps the kiln and can leave a gap. Some
> newer vents are spring loaded to keep pushing them up against the kiln
> bottom.
> To test an under the kiln vent system, close the kiln and close all the
> peep holes. Close the top peep hole with some clay so it leave a half
> inch hole. Hold a burning match near this hole. If the flame is drawn
> toward the hole, it tells you that the vent fan is creating a negative
> pressure in the kiln and it will be drawing fumes out. If this works on a
> cold kiln and not on a hot kiln, the seal my be bad at the bottom between
> the kiln and the vent when the kiln warps from heat.
> 4. Finally, check the outgoing tubing to be sure there are no leaks at
> the joints or otherwise. If you find any breaks or leaky joints, seal
> them with high temp silicone caulking or glue. I was called to one very
> smelly school in mid winter. The roof vent was covered with snow and the
> kiln odor was blowing into the space above the ceiling tile and passing on
> to the hallway and adjoining rooms in the building.
> Many teachers have the kiln finish off at night so the air is clear by
> morning. If it goes off about two hours before you come in the morning,
> the residue should be clear if you have any kind of exhaust working.
> Always check first thing in the morning to be sure it went off. I have
> seen too many things go wrong with automatic kiln controls to tell all the
> stories here. If firing on Friday night, it means a phone call or a trip
> in to check it on Saturday morning -- not Monday.
> Marvin (firing kilns for 47 years and still breathing fine)
>>>Pottery is often decorated using overglazes, china paints, and lusters.
>>>However, to make them easy to brush on, many of these materials are
>>>suspended in TOXIC aromatic hydrocarbons. I use lusters, but only when I
>>>can sit outside with the wind from my back to carry the vapors away. If
>>>you can smell it, your brain is being effected. It is not safe to use.
>>>Firing also releases the toxins.
> ---
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