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

[Hank Murrow]

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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