Wednesday, 7 October 2015

Testing iron red glazes

Now for my pet project...

The above picture is a detail of a bowl I threw in iron-rich stoneware and glazed in kaki glaze (the recipe actually called it a red oilspot). This amazing result was a complete accident, as some of the best discoveries often are. It was fired in my friend's hybrid kiln in Taipei in 2013 when I was still living there. It was way overfired - he thinks maybe it went as high as 1330 Celcius - if you are not in the know, let me explain that it is hard to know as witness cones show heatwork, not temperature. My friend fired a very slow and  complicated  oilspot schedule. The glaze ran all over his shelf and pooled very thickly at the bottom of the bowl, but where it ran it created beautiful shades of red, brown, orange and black.

I have been trying to recreate it over the last year here in my electric kiln in Brussels, Belgium - so far still in vain. Though the piece above was fired in a hybrid kiln in medium reduction, I believe I can reproduce something close to it in an oxidation atmosphere. Iron reds usually do well in oxidation, though I reckon it would benefit from a short period of reduction near peak temperature. Well, too bad - cannot do that in my little Nabertherm kiln. I sneak a test tile into most 1280 firings. (1280 Celcius being my highest firing). I refuse to give up! This glaze is worth the hassle to me, because its colours are created purely by additions of talc, bone ash and iron - there is no lithium as you have in many beautifully varied iron red/ kaki recipes.

My experiments have led to one unforgettable/unforgivable disaster:

 I have not recovered that shelf yet.

And many mediocre results - but let me focus on some that show promise:

What I am looking to create is an oilspot or hare fur effect (like on the inside of the bowl above) where the iron will really work its magic and separate into many colours when it starts running. I want to reduce the metallic sheen. And I want it to stop running so much and ruining my kiln furniture!

It is a tall order.

Recently I think I may be onto something. In my next test I will lower the bone ash and iron content and replace some of the talc with magnesium. We shall see if the kiln gods are with me next time.

No comments:

Post a Comment