[Clayart] Sugar reduction of glazes

Tue May 24 01:33:13 UTC 2022

Has anybody ever tried Aspartame in place of sugar.
Edouard

-----Message d'origine-----
De : Clayart [mailto:clayart-bounces at lists.clayartworld.com] De la part de L TURNER
Envoyé : 23 mai 2022 18:17
À : Clayart international pottery discussion forum
Objet : Re: [Clayart] Sugar reduction of glazes

The Hanford experiments were clear on the use of sugar as a reduction ingredient in the containers where the experiments were conducted with temperatures of between ~800 and ~1200 C  (cone 015 to 6).

My experience with cooking at home and over a campfire: overheating of sugar during cooking produces first a dark syrup followed by a strong "black stuff" stuck wherever it touched something; seldom did the sugar burn clean in a skillet.

Properties of sucrose:
The overall data from two reliable databases indicates that sucrose decomposes to water and carbon; the carbon is solid material.  Sucrose as a "dust" (suspended in air) will, in adequate air, rapidly be converted to carbon dioxide and water vapor plus a significant increase in volume (aka
explosion) as demonstrated in several sugar silo explosions; compacted as a solid material the reaction will first decompose to water vapor and solid carbon; however in a compacted material the temperature raise will be slowed similiarly to the reactions of normal glaze reagents that produce vapor as part of the conversion from solids to a viscous melt.

I have previously used sugar as an ingredient in a clear glaze based on Portland cement with no problems; the glaze was used over half a semester as the base for a clear, a cobalt blue, and iron glazes with the same base glaze ; however the firing was in an gas fired cone 10 reduction kiln (was a very good glaze by the way) so that data does not provide any information on reduction (since the kiln was already in reduction); the experiment did say that sugar does not screw up a glaze or make a mess.

While on the topic of reduction;  Hank Murrow, Mel, and others have made an important observation that oxygen does not significantly migrates back into the glaze; otherwise the reduced elements below the surface would have been reoxidized.

Since not even "the Shadow knows" I will try to schedule a test some time this fall. If you are interested, let me know.

LT

On Thu, May 19, 2022 at 6:08 AM Robert Harris <robertgharris at gmail.com>
wrote:

> When talking of local reduction, the most important part is the 
> sealover temperature of the glaze. Any reduction needs to continue 
> until this temperature, otherwise reoxidation will occur.
> A few points of consideration -
>
> In normal reduction firing carbon monoxide is the reducing agent. 
> There is no reason to believe that this is not also the case with 
> localised reduction from SiC. It is likely that thermal oxidation of 
> SiC produces carbon monoxide which then reacts with copper and iron oxides etc.
>
> My best ability of recall says that under normal conditions 
> (atmospheric pressure, low water content), thermal oxidation of SiC 
> starts to occur around 1000C (1832F) and is slow - mostly because it 
> is constrained by the crystal structure. Carbon oxidises first on the 
> planes of the crystal. If you want to read more about thermal 
> oxidation of SiC the most extensive research has been done under the 
> auspices of the Nuclear Regulatory Commission (NRC) as SiC has been 
> evaluated for use in cladding for nuclear reactors. This temperature 
> profile takes place around or after sealover temperature of most stoneware glazes.
>
> Thermal oxidation of sugars to carbon monoxide probably starts around 
> 400C (752F). In a normal electric kiln it will probably all have 
> burned out before sealover occurs and therefore allows re-oxidation of 
> copper and iron oxides.
>
> A final bit of personal evidence. I have tried to use powdered 
> graphite. As far as I can tell it all burned out, but I have 
> successfully used Silicon Carbide with the same recipe. Aluminium 
> powder also works. Years ago I also bought some powdered silicon, I 
> have never tried it, as soon after I bought it I had access to a fuel fired kiln.
>
> If you can find an organic compound that does not start to oxidise 
> until
> 700 or 800C (just as a guess) then you might have some more success.
>
> Robert
>
> On Wed, 18 May 2022 at 19:36, L TURNER <magnolia.mud.list at gmail.com>
> wrote:
>
> > Has anyone added sugar (or molasses) to a glaze to get  "local reduction"
> > in an electric kiln?
> >
> > the question derives from reading the PNNL-14063 research report on
> Hanford
> > waste vitrification.  Sugar was added to the test batch of the 
> > materials
> to
> > reduce some of the oxides to either metals or lower oxidation states.
> > The report does not provide a lot of details, but enough to at least
> think
> > about what glazes would the "local reduction" be useful.  Creating
> reduced
> > copper or iron oxides in areas might have some artistic value. Yea,
> copper
> > reds with Silicon carbide does work (sometimes), but a spoon of 
> > molasses
> is
> > easier to get, etc., etc.
> > Think about it.  and let's talk about it.
> >
> > LT
> >
> > PS one can find some interesting insights on silicate melts (aka 
> > glazes) outside of the usual box.
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