[Clayart] Too much Neph Syenite in a Cone 10 slip glaze for soda firing

[Vince Pitelka]

HI Hank - 
It could still happen.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net  
sites.tntech.edu/wpitelka/

-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Hank Murrow
Sent: Friday, May 4, 2018 8:58 AM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] Too much Neph Syenite in a Cone 10 slip glaze for soda firing

Dear Helen;

Fingers and toes crossed in Eugene, OR waiting to hear of your successful first firing. IT was different for me the first time, as I fired an old Alpine for the first time and having lost the vision of the cones, it went to C18 before I turned it off! Haven’t over-fired a kiln since, in some 3000 fires over a sixty-year span, though.

Good Luck Helen!  Hank in Eugene

> On May 3, 2018, at 12:46 PM, Helen Stone <helenestonepeony at gmail.com> wrote:
> 
> I did my first cone 10 soda firing this week in my new soda kiln, with 
> over
> 150 samples inside, including various mixes of native clays and native 
> kaolins.  For the samples, I used a slip recipe from Gail Nichols soda 
> firing book, but altered it.  This is because, for my lowest kaolin 
> content sample clay bodies, I did not think that they could last up to 
> cone 10, I thought that for they maybe would make cone 8 maturation.  
> These lowest kaolin content samples were 20% kaolin, others were 25% 
> and 30% kaolin with corresponding lower amounts of native clays in the 
> mix.  The reason that I thought that they could only go to cone 8 is 
> that, in and of itself ,one of these native clays typically fires to 
> cone 4 and a half, when fired by my friend, the salt kiln potter.
> 
> So I altered Gail's slip recipe.  She called for Neph Sy 10%, Clay X 
> 80% and Silica 10%, with Bentonite additions as a basic slip for Cone 
> 10, but really her firings go to cone 11.  So I foolishly put in Neph 
> Sy 20%, leaving the other items the same %, somehow thinking that this 
> would provide for a lower melting temperature, possibly at cone 8, 
> where was my head.
> 
> Tomorrow I will open the kiln and see what happened.  If the slips did 
> not melt properly, I will have to change my higher Neph Sy recipe to 
> accommodate one similar to that of Gail Nichols.  Any suggestions would be
> welcomed.   Because I have dry powdered slip mixes to the ying yang and
> cannot waste them.   Last ditch choice for me would be to possibly weigh
> each different dry powder slip sample and extrapolate from that, what 
> ratios  of Clay X and Silica and Bentonite I would have to add, in 
> order to bring the slip recipe up to be the same as Gail's recipe.
> 
> Thank you for your help.
> 
> Helen in Ecuador, on Rio Yambala, with happy cats
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