[Clayart] Learning to fire the Olympic and playing with glazes

Snail Scott via Clayart clayart at lists.clayartworld.com
Tue Jul 14 22:53:56 EDT 2015

On Jul 14, 2015, at 8:26 AM, Deborah Thuman via Clayart wrote:
> ... I tried the cobalt wash on a diatom box. Alas, I had to fire this piece to show me where I went wrong. When I brushed on the wash, I could have sworn there was almost no color on the piece. I was wrong...

Cobalt is such a strong colorant, and darn near invisible in its raw form when 
applied in thin concentrations. A single percent difference in amount can make 
the difference between baby blue and navy blue. 

When using cobalt as a wash, instead of using it 'straight', mix it with something  
-anything- to dilute it to a manageable concentration.  An engobe recipe, for 
instance, or just some clay and some frit. Use the cobalt in the same concentration 
you might for a glaze of the intended color - one percent or two, maybe, to start. It's 
still hard to see, though, so calcining it can help. Or...just buy it as a stain, already 
pre-calcined. This will give it more of a WISYWIG application - you'll see the 
blue instead of guessing where it's at. I have my students add food color to raw 
blue slips, to help visualization.


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