One of the things I wanted to investigate in this last batch of tests was whether I could achieve a semi-opaque white in a very fluid base glaze. I thought it might be nice as an additional liner glaze option or possibly layered under other glazes for effect. I wanted to try this with titanium dioxide. So, I took my base glaze and did a line bend from 5% TiO2 down to 0% in 0.5% increments. I chose Titanium (over zircopax or tin oxide) as it is reported to generate streaking effects and intensify colors. I already have a serviceable liner white, so I was really going for something else here.
In this particular base glaze (feldspathic, high calcium borate flux), 2% TiO2 and less does not even show up in the glaze (figure 1). It seems to make it bubble a little more, but no appreciable color change is evident. This is interesting as 2% TiO2 added to a basic cobalt blue glaze causes a marked change in the glaze (figure 2). This makes me wonder whether the “clear” 2% TiO2 glaze (figure 1, pot #5) layered under a blue or other colored glaze would cause any effects. I don’t particularly want to make up medium sized batches of each of these TiO2 glazes and try all 11 versions under my existing colored glazes. That’s way too much work. But I will choose one of these and try layering it underneath others.
Above 2% TiO2, definite streaking occurs (figure 3, pots 6-8) and above 4% (figure 3, pots 9-11 and figure 4), the titanium takes on a blue-ish tinge which, I think, is quite attractive. Unfortunately, the 5% TiO2 does bubble and it is quite pinholed. I am having a really hard time choosing between 8, 9, and 10 (3.5, 4, and 4.5% respectively). No. 10 (4.5%) is highly pinholed, but for layering, this might be ok as the overglaze would (hopefully) flow over the holes and seal them off. Also, bubbles popping through the overglaze are likely to cause streaking and lots of movement in the finished product. No. 8 (3.5%) is not pinholed at all, but is only really visibly white at the top of the pot where I double dipped it. The results of the blue test (figure 2) indicate that – for a layering glaze – you don’t have to be able to see the white for it to alter the color response. Ah, choices…
I always stick a few random tests in as well. I took my new and improved “Spruce Juice” and layered that over the Nuka that Robert came up with a while back (figure 5). It changes to a really nice turquoise and puddles quite nicely. I am pretty happy with this. This Nuka recipe does craze (tiny, hairline cracks), so it is limited to decorative use. Also, I was unhappy with my original Tenmoku glaze and have revamped it as well (figure 6). I love the super black mirror finish and how it breaks to rust brown. I think I might be finished with that one as well.
For all of you who really loved the “lapped black” (see our facebook for pics)… I have tried to recapitulate this glaze in several firings now. This last batch of line blends is still unsatisfactory in terms of the color response. I mean, they’re nice enough blues, they just don’t wow me. I want a blue that tonally matches my current glazes, but is not so dark that it just looks black. We’ll see next time!