Saturday, August 10, 2019

An August Wood Firing! About Ash Glazes.


Last weekend I managed to glaze fire some of the rather huge collection of bisque fired pots that has accumulated on my studio shelves over the past few years.... yes, years... some of them date back a long way now! It was the first firing of my wood fired kiln since March 2018.... such a long time..., and must have been a surprise for it to be coaxed back into life, and to have all the accumulation of moisture gently steamed out of its brickwork.

Fully loaded kiln before bricking up the doorway for the firing.


I was actually quite surprised that there weren't great clouds of steam escaping from every nook and cranny as the firing went on, in fact the old dragon was rather well behaved and climbed steadily to cone 10 in ten hours without protest or sulks!

After the firing, new shiny glazed pots!

Unpacking the kiln 3 days later revealed a goodish result over all, not the best firing I have ever done, but certainly not the worst! I had some nice ash glazes and iron red, but the copper reds were not good.

Saturated iron glaze with ash glaze splashes over it.

There is always something to learn from firing the kiln, and "bad" firings are often the most instructive of teachers as they do show where the boundaries lie between success and a poor result.

I have been peering at the graph of this firing and comparing it with the very good one I did in March 2018, and I can see that they are quite different regarding rate of climb, time spent above 1200 degrees, when I fired the kiln in reduction and so on. There are definitely things to keep in mind when I fire again!


Prior to glazing work for this firing, I went through my usual day of indecision and gloom as I thought about the work, and what glazes to put on them, and about the glazes I already am familiar with, and the tests that I wish I had done that I had not done regarding what glaze "A" will do when put over glaze "C" or "D". I felt very dissatisfied and frustrated, and the frustration was not just about technical matters, it was a much deeper one. I felt like I had lost touch with the glazes that were really "me", that really excited me, and expressed who I am.


In the midst of some hours of increasing introspection, I went in search of glaze tests that I did more than 10 years ago, the glazes were ash glazes. At that time I had done many tests of simple glazes made with wood ash, clay, silica, and feldspar as a result of being inspired by a book by Phil Rogers, called "Ash Glazes". When I was testing such things, I had not yet built my wood fired stoneware kiln, so I fired the tests in the electric kiln. Some of the tests did yield nice glazes that I later did use in the electric kiln, but... from what I know now, most of the glazes would have been far better in the wood fired kiln where they could have taken advantage of a reduction atmosphere.



Once my wood fired kiln was made, I really didn't explore the ash glaze thing much further.. life got in the way.. and my tests sat in a box gathering dust for a decade!

Ash Glaze tests all fired in the electric kiln to about cone 9 (these would look quite different fired in reduction in a wood fired or gas kiln.) You can probably work out what the recipes are from my shorthand on the back of each test. A (or WA)= washed wood ash, ABC = Australian ball clay, RC = red earthenware clay, CC = China Clay, LC = Local Clay, PF = Potash feldspar, SF = Soda feldspar, NS = Nepheline Syenite, CS = Cornish Stone, Sil = Silica, Ben = Bentonite, BF = Standard Borax Frit,


It was good to rediscover them, picking up the glaze tests and peering at them gently lifted me from my gloom, and I started to feel genuinely interested in trying them with some of my new work.

I made up a white Nuka-style* glaze (test A27 above), and some other ash glazes, and applied them to several pots to see what would happen.

White Nuka-style glaze over speckled ash glaze.

Nuka-style glaze over speckled ash over Shino glaze!

Wood ash 40, soda feldspar 40, red earthenware clay 20.

Whilst the results might seem a bit "quiet" for people with a taste for vivid colours, the earthy greens, red-browns, and lovely flowing icy white of the Nuka glaze, really spoke to me. The thing about ash glazes is that they are so much more than colour, they have texture as well, from smooth and flowing, to dry and stiff. The glaze is often attractively crazed as wood ashes contain a lot of alkaline fluxes that have a high expansion such as potassium, sodium and calcium. There is also an unpredictability to ash glazes, especially if the ash is unwashed, as different trees and plants have a very different chemical makeup, and will give a unique result when used as part of a glaze.

Some potters became connoisseurs of ash from plants in their local areas. I once had the pleasure of holding an ash glazed pot by the English potter, Katherine Pleydell-Bouverie (1895 - 1985), who had been a great pioneer and enthusiast in the use of ash in glazes. The pot was quite humble and unassuming in form, and had a lovely satin surface rather like that of a smooth stone that had been picked up out of a river. I was delighted to find this quote just now when writing about this, as it so rightly sums up the character of the pot that I held. "I want my pots to make people think, not of the Chinese, but of things like pebbles and shells and birds' eggs and the stones over which moss grows. Flowers stand out of them more pleasantly, so it seems to me. And that seems to matter most." Pleydell-Bouverie 

*Nuka glaze cone 8 -10 reduction
 This type of glaze was traditionally made with rice straw ash, which is mostly silica.

Not a lot of rice straw to be found around here in the South of the South Island of New Zealand, so this is my simple substitute which yields something that looks a bit like a nuka glaze, but uses fire wood ash.

40 unwashed wood ash (sieved dry through an 80 mesh sieve)
30 potash feldspar
30 silica

Good starting point for a wood ash glaze cone 9 or 10 reduction
As you can see there are many variations possible within this simple 40,40,20 ratio of ingredients.
40 wood ash (can be unwashed or washed)
40 feldspar (can be potash, soda, or Cornish stone, Nepheline Syenite)
20 clay (can be red earthenware, local clay, china clay or ball clay)

Speckled Wood ash glaze for cone 10 reduction
50 wood ash (washed or unwashed. Fine or coarse sieves for different speckles)
50 clay (china clay, ball clay or mixture of the two)

To Finish
Here are photos of the 3 ash glaze pots that I have shown close up details of above. Each one is about 7 inches (180mm) tall. I will post other photos of work from this firing in a separate blog post in the next few days.




8 comments:

gz said...

KPB was a marvel to meet..and Nora Braden (think I have her name correct?)
Sometimes the shape of their pots is nothing to write home about, but the glazes quietly sing.
Good to hear that your Dragon is firing again. The drying out will have affected the firing..but don't forget to note the weather in your kiln log!
I love Nuka..it can be a bit much on its own, but combines beautifully. More ash glazes please!!
Eric Mellon did much on ash glazes istr..did he write a book too?

Btw we have been invited back to Aotearoa/NZ....to Whanganui. Not sure if we can afford it this year, but you never know....

Michèle Hastings said...

I like the layering of nuku over your other glazes. We have a glaze that's called "nuka" but it isn't anything close in formulation to the real thing. We fire a lot of ash glazes in our gas kiln. When we were heating with wood Jeff was very particular about only burning one type of wood at a time because he didn't want an ash of mixed woods. I was always afraid of messing up his plan when lighting the stove!

Melissa Rohrer said...

Very nice. I also appreciate the earthy glazes.

Peter said...

Hello Gwynneth,
How wonderful that you have met KPB and Nora Braden! I can imagine them excitedly combing the countryside for suitable plant material for making ash for glazes.
Eric Mellon did some lovely work, I've only seen it in books and online unfortunately, but very nice to see the way he brought together the skills of the potter and the painter in the same work with his sensitively drawn images of the female nude as part of the decoration of a bowl or pot.
It will be lovely to see you again if you manage to get back to NZ, we did enjoy meeting you and the Pirate very much indeed.


Hi Michèle,
I do enjoy seeing the ash glazes that you and Jeff use. My ash is usually mixed, as we burn what ever we have available, but I can understand the attraction of using just one species at a time. Our ash does tell a story though, as the mix changes through the year. There is a portion of oak ash in the mix at the moment as we had to have some trees taken out that were much too close to the kiln. (I'd planted them years before taking up potting and building the kiln!).

Hi Melissa,
Good to hear from you. It is nice to be using ash glazes again, they do seem to suit clay very well, I think they are "timeless" in the bigger picture of things, even if they go in and out of fashion in the short term.

Linda Starr said...

I can't believe you had so much bisque lying around, bet you have more room in your studio now, ha. the purple you got with the one ash combo is wonderful. I know how you feel about what glaze to use on what pot, then when I take them out of my kiln if I don't like it I am wishing I had used this or that one instead. I have a big bag of ash I bought years ago thinking I could use it only to find out it must fire much higher than I fire to melt and as you mentioned wood firing is better, now the ash sits in my cabinet waiting for who knows what. I have heard from other potters that rice ash is a desired one to use, but what do I know. Your tea pot is wonderful to see close up as well. I fired this week and I can't even remember the time before that, I know it was last year some time. Hope you are doing well.

Peter said...

Hi Linda,
Lovely to hear from you. I still have lots more bisque to go.....! I will try to do another firing fairly soon to help work my way through the pile! :-)
I also have a big bag (or 3!!) of ash from some time ago hiding in a dark corner of my studio..... but really nice for me now to be able to think of it as an asset, rather than as a nuisance! Whilst ash glazing does seem to be mostly done at high temperatures, I have heard of potters adding a little ash to low and mid temperature glazes as well. Wood ash is mostly various fluxes and silica, so it should be possible to come up with something that would work OK with a little clay to help control the melting point of the glaze and how runny it is, and probably some frit or feldspar to help make more of a useful balanced glaze. Next time I glaze fire earthenware I should try to make a few test glazes with ash and see what happens...
The health side of life has been a bit difficult, but I get a little bit of potting done some days, and it is nice to still be able to celebrate an occasional firing!
Best Wishes to you,
Peter

PP said...

I really do like your nuka glaze - the variations within it, and the way it bleeds around the edges. Very lovely. It looks stunning over shino - like a river delta. I spent the whole of last winter saving the ashes from various fires so I too could have a go at making it, but the ash is still sitting there! Maybe this year...

Peter said...

Hi PP,
Do use the ash you collected, it is a delightful material, and so much can be accomplished with just the addition of some clay, feldspar, and maybe extra silica or a dash of dolomite or whiting for "flavour"!