[Clayart] Offgassing bisque

David Woof woofpots at hotmail.com
Sun Jan 30 03:30:16 UTC 2022


Hi Robert, All,
I was just going to post and offer a related suggestion when I opened Robert's post: my contribution is that if there is any friction caused heat build-up then the heat expanded air molecules, if trapped under a tight cover seal, would hiss or woosh out on opening the canister.

It wouldn't take an extreme heat rise to create a small but measurable positive pressure.

Robert my dinner is waiting and I can't take time to wrap my head around the lubricating effect caused by the water vs possible friction heat from the porcelain objects and the polishing medium in water..

Perhaps you or someone would run this thru to a logical conclusion if you think this has merit.

Now Woof aller manger vite!!!  ..............................................................................................................................................

Apologies, but my Muse is also hinting" j'ai encore une "in the studio!!!   What she wants she gets!!!

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________________________________
From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of Robert Harris <robertgharris at gmail.com>
Sent: Saturday, January 29, 2022 7:17 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] Offgassing bisque

I was assuming that the tumbling was done in water. It sounds like everyone
else is assuming it's done dry. (at least I'm assuming there wouldn't be
much frictional heating with water).
Which is it!


On Sat, Jan 29, 2022, 16:45 paul gerhold <gerholdclay at gmail.com> wrote:

> I would look at what chemicals are used to color the bisque. Maybe some
> decompose at low enough temp that just the friction heating would cause
> decomposition to occur.
>
> Paul
>
> Sent from my iPad
>
> > On Jan 29, 2022, at 12:40 PM, Robert Harris <robertgharris at gmail.com>
> wrote:
> >
> > Pretty much the only likely chemical reactions are ones that give off
> CO2.
> >
> > Something like a bicarbonate reaction with acid  Not saying that's what
> it
> > is, just more likely. See if the gas puts out a match. You could see if
> > adding a bit of vinegar speeds up the evolution of the gas.
> >
> > Only other possibilities, both fairly farfetched would be hydrogen (match
> > wil light it - stand back) or hydrogen sulfide (which would be really
> > obvious).
> >
> > Robert
> >
> >
> >> On Fri, Jan 28, 2022, 08:44 Bryan Johnson <bryj at cheqnet.net> wrote:
> >>
> >> When I tumble polish bisqued colored porcelain jewelry I need to "burp"
> the
> >> barrels after an hour or so due to the gas given off by the porcelain.
> What
> >> is the gas?
> >> It doesn't happen after high fire.
> >> Bryan
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