Category: oil spot

Limestone Black Glazes

Not exactly Oil Spots in the truest sense, these two variations were concocted and tested along with the rest of my oilspots glazes. Both of these recipes utilize some local dolomitic limestone I found and incorporated into the recipes. If you want to re-create these, using a mix of 1/2 and 1/2 Dolomite and Limestone will get you very close.

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Dolomitic Limestone from Cache Valley, UT

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Shizuku Yuteki Variation

Here’s another Oil Spot I put up on Glazy.org.

You might notice that this one has a significant addition of Cobalt, half and half Custer (Potash) and F4 (Soda) Feldspars, calcined talc, and 2% Manganese. Typical that I changed too many things to give a really useful side-by-side comparison. But I suppose when I’m coming up with new variations, that’s always been my style.

2 Shizuku Yuteki Variation
Left: Underfired and immature. Cone 9/10. Right: Super long and hot cone 12 firing, with plenty of peak soak time.

Some observations on this one:

Cobalt goes a long way and pretty dramatically alters an oilspot. With a  .25%-.5% addition you get a nice shift from brown and russet glaze matrix to a darker solid black glass. Beyond 1% you can get some really nice silvery qualities to the spots. The drawback is that the more you add, the more refractory the glaze tends to get – and the longer it takes for the glazes to heal.

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Epsilon Phase Iron in Tenmoku

For those of you who are really interested in Oil Spots, there’s an article from 2014 that I think is worth a long look. This particular article was what got me interested in SEM microscopy when I was in Grad School:

Learning from the past: Rare ε-Fe2O3 in the ancient black-glazed Jian (Tenmoku) wares – Nature.com

Abstract

         Ancient Jian wares are famous for their lustrous black glaze that exhibits unique colored patterns. Some striking examples include the brownish colored “Hare’s Fur” (HF) strips and the silvery “Oil Spot” (OS) patterns. Herein, we investigated the glaze surface of HF and OS samples using a variety of characterization methods. Contrary to the commonly accepted theory, we identified the presence of ε-Fe2O3, a rare metastable polymorph of Fe2O3 with unique magnetic properties, in both HF and OS samples. We found that surface crystals of OS samples are up to several micrometers in size and exclusively made of ε-Fe2O3. Interestingly, these ε-Fe2O3 crystals on the OS sample surface are organized in a periodic two dimensional fashion. These results shed new lights on the actual mechanisms and kinetics of polymorphous transitions of Fe2O3. Deciphering technologies behind the fabrication of ancient Jian wares can thus potentially help researchers improve the ε-Fe2O3 synthesis.

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Leonard Smith – Modern Jian Ware

Oilspots

Friend and fellow Oilspot fanatic Leonard Smith has put together some great videos on Chinese glazes. I’d highly recommend checking out his Youtube Channel and taking a look. This one shows a Chinese potter reduction cooling for iridescent oilspots!