Friday, November 1, 2013

a study of crawl glaze pieces

Recently I mixed up a new barium glaze recipe that was noted as a lowfire cone 04 glaze.  Note, I used midrange porcelain for my testing bodies.
Interesting color response that I loved, but the feel was a very dry matte and the surface had a crawl effect (although it looks crazed it is not, the edges are smooth)  on the areas where thicker, the glaze turned a very vibrant purple and crawled, on the thin areas it was a lovely turquoise.   The color was brilliant though and I wanted to pursue perfecting the glaze to a smoother surface, in hope of keep the same color response.

I started by simply firing another piece to cone 5,  the glaze did not run, did smooth out a bit, but it still crawled in larger patches and  the brilliance in color was subdue.  The mottled look inherent of the nature of a matte finish.  Still I wanted this color, but in a silky soft finish. 
I mixed up another 1/2 batch (#2) this time increasing the flux via added neph and barium and continued firing at cone 5-6, no more low fires.   More neph seemed to make a deeper inky blue while more barium a lighter denser denim blue. 
Smoother, but where's the purple?  One more batch (#3) that I poured 1 cup of mixed epsom salt water solution into as part of my liquid, hoping the MgO would brighten the color up.  Well it did, but now we're back to a crawl effect.  Apparently all the mgo in the epsom salt water was overkill.  I will continue on, not making that mistake with the epsom salts and report new findings later on.  During these tests, I notice that on the pieces with a wash of red iron oxide at the base, a light green was occurring, so I also tested a few pieces that show the color response when iron is added.  I also had a green results over iron bearing clay bodies.

If anyone knows what ingredient will increase the purple, please feel free to leave a comment and I will play around with the amounts.
Ingredients in the glaze are Barium-Neph_EPK-Flint-Lithium-Copper
Happy Testing!


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