|Monthly Tech-Tip |
The inside glaze of this cone 10 reduction fired mug is a base transparent glossy, G1947U. It has no additives to color, opacify or variegate it. That being said, the speckled body is making for a more interesting aesthetic on that inside surface. The outside glaze is a far different story. It is a base - a silky matte, G2571A. But it has additions of 3% titanium dioxide and 6% Mason 6021 red stain (this version is numbered G2571D). Of course the red coloration is from the stain. But the titanium is making the visual magic here, it is both an opacifier and a variegator. It is clearly producing phase changes and crystallization. One of the glass phases is redder and more transparent (the brighter red spots). Another phase is a much lighter opaque pink.
These porcelain mugs have the same glaze, the one on the left was fired at cone 10R (gas), the other at cone 10 oxidation (electric). This is our standard cone 10R magnesia matte, G2571B. We have added a 5% Mason 6021 encapsulated red stain and 4% titanium dioxide (producing recipe code number G2571D). While the reduction version looked good the oxidation one turned out much more vibrant. And it feels much better, being very pleasant to touch. The marbling is a bit excessive so in G2571D1 we reduced the titanium by 1% (and increased the stain by 1%). MgO matte base recipes are very receptive to this type of adjustment and they work across a wide range (from low to high temperatures). Titanium is much better for variegating bright colored glazes than rutile, because the latter contains lots of iron that muddies the color.
G2571A - Cone 10 Silky Dolomite Matte glaze
A cone 10R dolomite matte having a pleasant silky surface, it does not cutlery mark, stain or craze on common bodies