Monday, 15 August 2011

Matt glazes fresh from the kiln!

I tested several different matt glazes in the latest electric firing, and pulled out the results this morning. The oxidised satin matts came out rather dull with little surface variation, but I was delighted with this piece, which was fired in reduction in my saggar.

Carved vessel, approx 4 inches tall. Satin-matt glaze.

I've uploaded a video of this piece on Youtube: . This glaze contains red iron oxide and rutile, and there are even a few touches of rutile blue on the inside below the rim, just visible in the photo. I really like the way the glaze has run over some of the carved ledges, and the variety of yellow-orange-brown colours..also the way it's broken darker on the edges helps to define the form.

The next piece was fired in oxidation with a matt ash glaze. It's based on a John Jelfs recipe but I used oak ash rather than mixed ash, and marble dust instead of whiting. The thing I found amazing about this glaze was its' brushability. I only made a small sample, so I brushed it onto the outside, and poured the glaze inside. It applies incredibly easily, leaving practically no brushmarks..I'm wondering if the marble dust helps in this respect, as it's so finely ground and may help with suspension. Only two thin  coats were applied, which has allowed the body colour to burn through as a dark red-purple. The first piece was fired in oxidation, the second in reduction. Why is the glaze fired in oxidation more matt, I ask myself? Maybe because iron acts as a flux in reduction?

Small cup, approx 2 inches tall. Matt ash glaze

Carved sake cup, approx 2.5 inches tall. Matt ash glaze.

I'm not sure whether I prefer the oxidised or reduced ash glaze..they are both attractive but in different ways.

As is so often the case, there were some disappointments when opening the kiln. I tried a new blue-lavender glaze, which should have come out a bright glossy blue with satin lavender speckles where thicker..I had already tested it and it worked perfectly, but on the actual work I glazed, it came out a light blue-purple colour with practically no lavender speckling. Quite pleasant in itself, but not particularly interesting to look at either. Basically, it wasn't applied thick enough, which really surprised me as the glaze looked fairly gloupy and I dipped some of the cups twice. I think I need to re-test with a thicker glaze slop, and next time, measure the specific gravity..then ensure it's accurate each time I use it.

Update: I went back to the glaze today to give it a stir up, and the ingredients had settled into a rock-hard layer at the bottom of the took me a good ten minutes to get the whole mixture moving again. So I decided to mix in some bentonite and CMC into the slop to help suspend everything, and now it's looking thick and creamy; so much more useable as a glaze. It's pretty difficult to mix these suspending agents into the glaze once the other ingredients are wet. It took me an hour or so to get rid of hundreds of lumps with a hand blender..definitely not recommended. Hopefully worth the effort though..I'll post the results of the next firing with this glaze.

Mug with blue-lavender glaze. Approx 4 inches tall.

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