Reduction Results: Rethinking Surface

This morning, after nightmares of flooded glazes, collapsed shelves and shattered kiln elements, I opened the gas kiln to reveal the first batch of my exhibition module work that’s made it through to be glazed. I have mixed feelings about the results but seeing the finished coloured vessels is a huge aid in understanding how I want them to look, even if I haven’t quite reached the point where I’m happy yet. The vessel above has been sprayed with three layers of shino over three of tenmoku. Although oxidising atmospheres are necessary for oil-spot glazes to form in iron rich glazes, by layering these two glazes I found I could recreate a very similar effect. More different to my original tests however is the pink vessel (see below) which I expected to be a slate-like blue from a thin oxblood over a shino. I think perhaps the copper oxide didn’t reduce so much in my test since it was so small. Putting such a feminine, glossy, vibrant pink glaze on an almost violently disfigured, masculine form is a striking juxtaposition. I originally did think of juxtaposing the Peter Voulkos style slashed and punched vessels with delicate, child-like pastel colours to create an unexpected clash. I then chose instead, based on my prior research into reduction glazes to use more traditional, recognisable japanese style tenmokus, shinos and ash glazes so that there was some link to the familiar ‘humble’ functional vessels like the ones we saw at the Leach pottery and that you find in so many studio ceramic collections. I hoped deconstructing these vessels and patching them up would be a metaphor for my own deconstructing and redefining what it means to be a potter and to be part of this long tradition.

The spherical vessel form above is so far, for me, the most aesthetic of all the vessels I’ve made. Perhaps something about the three sections conforms to the golden ratio or perhaps it is simply something to do with the notion of perfect roundness which I’ve often mused about on this blog. Either way, my next stage is to make more of these round forms, some narrower, some larger. The construction is very simple – two bowls stuck together with a thrown and spliced collar. Cutting and sticking back together the pieces as much as possible is also something I must do. The brown vessel below shows what happens when I keep the manipulation to a minimum – there is nowhere for the glaze to catch and pool or break on the edge to a thin wash. The top vessel here however has a beautiful quality of lines which reminds me of the patchwork tarmac in the pavements of Cardiff that I walk on my way to university and back each day. Scars and layers speak of the passing of time.

Since I usually pour or dip glazes, I found it difficult to know how many layers of glaze to spray. Six layers is perhaps not enough although I do like the even coverage achieved with the spray gun. Also unpredictable though is the way the glazes will behave in the gas kiln, even if they’ve been tested many times before. The shino on the jar below was poured on but unlike the orange metallic sparkles like on my previous pieces, this one only turned a crackled off white. These deformed jars are another shape I want to play more with and that will be quick to mass-produce. Since time is becoming of the essence and I’m struggling to control how the glazes look, I plan to mix up six or so oxidation glazes with matte or satin surfaces to layer and test next week. These firings will give me more control of colour and also a quicker turnaround. I’m drawn towards the ridiculousness and humour of these bulky, awkward vessels decorated in soft pinks or baby blues. I like the sleekness and oily voluptuousness of the fake oil spot vessel too though. Hopefully by the end of this week I will have more clarity about the surfaces qualities I want and what they should communicate.

DSC06366 (561x800).jpg

Advertisements

L6 Term 1 Technical Project: Reduction Glazes

Images and Key in the link:
Technical Project PDF

I began this term with the intention of developing a series of ash glazes with the hope of getting similarly expressive effects to those in the wood kiln at HDK. The project would also link in with my growing interest in ‘non-spaces’ through using plants from hedgerows and Cardiff’s invisible edgelands. Looking at the ash glazes of Bernard Leach and Katherine Pleydell Bouverie, I admired the quiet, subtle colours and how they work in a calming way on the viewer. Over the summer I collected together a few different ashes – from our log burning fireplace at home as well as from bracken and rushes I had sourced in the countryside in North Wales. I dry sieved these ashes without washing as I had read in the Phil Rogers glaze book that it wasn’t necessary to wash ashes.

Using the simple 60:40 ash to feldspar ratio recommended by Phil Rogers, I experimented with different feldspars, discovering that Potash crazed the most. I also discovered that increasing the proportion of China Clay made the glaze more matte (Test No1.1). Unfortunately the glaze application on the test tiles is patchy since the tiny amounts of ash I had to work with meant the mixtures ended up containing too much water. I left them to evaporate overnight but the small amount of ash meant I couldn’t get a very thick coverage. A second series of line blends (Test No1.2) was made to see what happened when I added increasing amounts of Potash Feldspar to different ashes. Ideally I would have added increasing amounts of ash instead since these results are too similar. The problems I had with obtaining enough ash led me to work with different glazes instead. All my ash tests were fired in reduction although I did test them in Oxidation too but they were colourless.

I liked one of my ash glaze tests very much because of its matte quality, strong iron speckling and mint green colour (Ash glaze A6 on the PDF) so as result decided to experiment with creating glazes that had a similar quality of subtlety and softness. I came across a glaze I had adapted from Jeremy Jernegan’s dry glaze handbook last year. The original glaze had been a matte white reduction glaze with Potash feldspar being the main ingredient. I had adapted the feldspars (as I did with the ash glazes) and discovered that adding Nepheline Syenite instead created a shiner, more viscous glaze (probably because it is higher in alumina than Potash). As I hoped to use these glazes on functional jars and bowls I didn’t want them to be too matte and flaky.

The original glaze is white however with Nepheline Syenite it becomes blue-white with patches of pink flushing depending on the reduction and application. I wanted a series of glazes with a similar satin quality but in different colours so added metal colourants to the base recipe in proportions as shown in the PDF (Test No2.1) and then, deciding these were too dark, created a Triaxial Blend with the Grey-blue, Turquoise and the lighter base glaze. I added 4 brushed on layers to each of the 16 tiles but unfortunately the results are a lot drier than I expected, not really suitable for functional vessels. The darkness of the glazes is probably a result of using Reduction St Thomas which is a darker clay body than the usual white St Thomas, which I chose because of the iron spotting it encourages. The dryness of the glazes in this test could be a result of them being on the lower level of the gas kiln where they perhaps didn’t quite all reach vitrification temperature.

Having never done a glaze technical before I felt a bit lost as to where to begin and how to alter glazes to get the results I wanted. Although the idea of using natural materials seemed attractive as it fitted with my philosophies of material vitality, finding the materials is such a dedication that it didn’t seem to be practical with the large quantities of glaze I needed for my functional vessels.  This project has been valuable to explore how colourants can impact glazes though and made me confident using the reduction kiln which I used for the first time this term.

 

Gas Firing Gallery

_MG_3792 (798x800)

Eight weeks into this first term I’ve succeeded in getting two loads of work fired in the little yellow gas kiln, although I haven’t quite been able to fill it myself yet and have relied on sharing space. I’ve been focusing so far on two simple forms – bowls for the Llantarnam Grange project, alongside jars which I began experimenting with over summer. Drawing from my experience of wood firing at HDK I am attempting to create a collection of classic/timeless and uncluttered shapes on which the activity of the glaze is brought to the foreground. Hopefully my exhibition statement for Llantarnam Grange can shed light on my thinking process:

Working with clay can teach us the value of patience, something which has become scarce and undervalued in our current society. The experience of time in relation to making is central to my practice. Through the stilling of clay as it slowly centres on the wheel-head, I enter into a different time zone where the material has control over my experience.
Throwing on the potter’s wheel becomes a method of quiet introspection where tensions in my subconscious manifest themselves in the finished vessels.  I find a place of refuge in this sphere of stillness, a meditative zone reflected in the soft curves of the forms and subtlety of glaze.
My practice is characterised by the balance between imposing my own design on the clay and surrendering control to the vitality of materials. Rather than painting on patterns, I prefer to leave the surfaces of my pots at the mercy of the kiln. Flames from the reduction firing leave traces of the action and movement of the firing process in the form of flushes of colour and fluidity of running glaze.
As a result the vessel surfaces become as American writer Harold Rosenberg said of Abstract Expressionism: ‘not carriers of images but [carriers] of events’.

My intention originally was to undertake a technical in researching ash glazes however after a series of unsuccessful line blends and a realisation that brushing on the glazes resulted in patchy, unattractive finishes, I have decided to focus more broadly on the effects I can achieve in reduction with other types of glazes. I realised that the large quantities of ash I would need to glaze the amount of pots I had would be difficult to get. The unpredictability of ashes from different sources meant my tests would be largely pointless unless I had a singular plant source. Upon visiting the Leach Pottery I discovered that an ash glaze made from one type of plant ash can vary wildly in colour depending on whether the plant comes from a heavily mined area or not since pollutants in the ground can affect the chemistry. Although I embrace unpredictability to some extent in the way the glaze varies over the form with iron spotting from the clay body, pooling in the centres of bowls and crystallisation on the glaze, I want some idea of what the glaze will look like.

All the glazes above result from layering one or a couple of the five glazes below:

Chun, Celadon and Shino – Tested at HDK
Matt pink Nephelyine Synetite Glaze 
Phil Rogers ‘Fake Ash’ Glaze :

Potash Feldspar      19
Whiting                    31
Talk                           2.4
Bone Ash                  2.4
Ball Clay                    6
Quartz                        9
Cornish Stone           15
China Clay                 15

I had a lot of trouble with a Derek Emms red reduction glaze recipe. The heaviness of the copper carbonate meant the suspension was terrible and the sediment fell to the bottom immediately no matter how much I mixed the liquid. I tried dipping, pouring and layering but the red was very patchy still. Perhaps this was due to the atmosphere of the kiln being not reduced enough though.
Although I’m happy with the subtle qualities of these glazes so far, without the right light the quiet shades of green, blue, pink, purple and red  can end up looking dull and grey. My next step will be to work with the same body (Reduction St Thomas) but applying a porcelain slip to the surface before bisque. Hopefully the colours will be a little more vibrant on a whiter surface. I’ve used a slip recipe from Jasper, adding 10% Potash Feldspar to porcelain to stop the slip cracking with shrinkage.

It might be useful next time I fire the measure how much the clay shrinks with each firing. – Measure Jars on the bisque shelf.

First Reduction Firing

Last Friday I fired the little yellow gas kiln at CSAD for my first time. Starting from about 8.40am the kiln climbed fast to begin with (up to 220C by 9am) and then rose steadily by about 100C per hour, a little slower than in previous weeks because of fluctuations in gas pressure (probably because gas was being used in the foundry). At 1000C, just before 1pm, the flue at the top back of the kiln was covered over in order to create a reduction atmosphere and was left this way for most of the final part of firing. As you can see in the image below two large pyrometric 1280 (09) cones were placed in the spyholes in the front top and back. By 3pm the top cone had completely melted while the bottom one was still only bending a little so in order to reach an even kiln temperature Gemma opened up the flue at the back which had been covered for reduction, encouraging air flow in the kiln. The firing was finished by 3.20pm.
In order to get a better impression of how the gas kiln behaves it could be an idea to place cones at the back on the right side too to see if there are hotter or cooler spots. Since the pyrometer was placed in the right side of the kiln and only read 1237C when the top cone was gone, it suggests to me that the right side might be a little cooler. It might also be valuable to place a 1300C cone at the top too to get a more accurate reading.

I was a little disappointed upon opening the kiln on Sunday since lots of the glazes hadn’t behaved as I hoped, although there were a handful of beautiful bowls and jars – my own nephyline syenite matte pink glaze worked particularly well. The main problem was that lots of the glazes were applied too thinly. My glaze application has improved since first year when I was painting them on and had lots of patchy results. Now I make a big enough batch of glaze to dip the pots in and this results in a much more even coverage. The chun and celadon which I had tested in Sweden turned out ugly patchy browns but perhaps they were just not thick enough. The best pieces seemed to be the ones most enclosed in the centre of the kiln shelves. More reduction could have been encouraged by packing the kiln tighter or even putting work in saggars. The insides of the lidded jars had a lot more brighter colours than the outsides because they’d reduced better.

While I only used one layer of glaze on the vessels, I tried layering different glazes on the test tiles above and the results turned out to be a lot more exciting this way. The shino over matte pink results in a matte lavender while the pink over chun creates a purple/blue crystalline – like glaze breaking to pale yellow where thin. The pastel colours in blues, greens, pinks and lavender have a quality of delicacy, lightness and quietness much like the glazes of Katherine Pleydell-Bouvarie. I’m drawn much more to the matter surfaces and they way they soak up the light in a soft, introverted manner. Somehow these surfaces feel more organic than the glistening, glassy ones which have an almost sticky, plastic texture. Shinyness distracts from the form too.  My next step will be to experiment with overlaying these glazes on vessels in a gas firing hopefully later this week.

Blue flames and broken fingers

Inspired by the pit firing on the Pottery throw down, Nina, Nam and I tried our own smoke firing over Easter with the help of the fabulous Ian Hinchliffe, potter at Quarry Pottery in Corris Craft Centre. We took a similar approach to the oil lamp bin firing Mick Morgan helped us with before the holidays – lining a bin with newspaper then dried wood chopped down as kindling.

The pots were wrapped in copper and steel wire then generously sprinkled with copper carbonate, cobalt oxide, black nickel oxide and a mixture of blue, yellow and pink commercial stains. Dried ferns, pine needles, leaves and banana skin were also added before they were wrapped up in tin foil. Once surrounded by the kindling we set the bin alight though the holes in the bottom and kept adding wood for a good few hours, the metal gradually turning red hot.

More stains, salt and oxides were sprinkled on during the evening, which, if they didn’t make much impact on the surface colours, definitely made for some spectacular electric blue coloured flames for us to watch. The experience of sitting around a fire with a group of people as darkness gently fell over the welsh hills, our shared hopes invested in our kiln babies and mesmerised by the flickering light and warmth of the flames, was an unforgettable experience. The raw power of the flames made me feel connected to something primal. I suppose our early ancestors would have felt the same awe sat around their bonfires at night. Although perhaps it’s just that every potter is a bit of a pyromaniac.

Opening the kiln in the morning, we were surprised to find all the foil burnt away but the pots hadn’t turned as dark as we expected. The colours came out best on the slipcast porcelain vessels with striking flushes of pink and constellations of smokey greys and browns on their smooth surfaces. Burnishing the pots beforehand would have improved the surface quality and leaving them in a reduction atmosphere for longer may have turned the surface darker.

Reduction Firing

Last week I had the chance to fire some work in a gas kiln for the first time and the results came out today. I don’t know much about how the firing works except that the kiln chamber is starved of oxygen so oxygen is taken away from the metal oxides, but I’d like to learn more. I’m attracted to the unpredictability of the glazes in this kind of firing.

I’d prepared two reduction glazes -the first was a Crystalline pale yellow/green semi-gloss with slight speckle (1280-1300C):

Feldspar                                 37
China clay                              18
Whiting                                   15
Quartz                                      10
Lithium carbonate               9
Titanium oxide                      9
Copper carbonate                 1
Zinc oxide                               1

The feldspar I used was potash and I added Titanium dioxide as a substitute for Titanium oxide. I’ve decided to use small thrown (off the hump) vessels or sections of discarded pots for glaze tests from now on because flat tiles can’t show how much the glaze runs.

20170213_162405-800x603-2
Crystalline yellow/green on Reduction st Thomas

The second reduction glaze I made was a Chun type pale green glaze with crazing:

Potash feldspar                                  45
Quarts                                                    25
Whiting                                                  17
China clay                                              9
Bone ash                                                 2
Dolomite                                                 2
+ Red iron oxide                                    1

The colour was subtler than expected but I like it’s fresh, quiet quality. I find the random speckles of dolomite glazes like this one attractive.

20170213_162333-800x645
Chun type green on Reduction st Thomas

Below: Buff stoneware. Two layers of Crystalline yellow/green glaze on outside with Duck egg blue raku glaze circles and Chun glaze inside. I like the roundness of this mug’s base in contrast to the sharper cylinder forms and the pulled handle balances it well.The ribbed texture from drawing up walls inside the form is highlighted by the way the glaze has pooled and draws attention to the way the mug was made on the wheel.

Reduction st Thomas. Duck egg blue raku inside and outside painted with crystalline yellow/green with chun type on top. Painted lines in red iron oxide. The duck egg raku glaze turned out a stunning, vibrant matt blue, I only wish I’d applied it to the outside.

Reduction st Thomas with blue slip splattered on top before bisque. Chun type green painted on outside with red iron oxide lines and turquoise spots. Inside crystalline yellow/green. I enjoy using the surface of vessels as canvases to explore abstract application of slips and glazes. This layering means I get exciting and unexpected results each time although I have to document carefully what I apply.

Buff stoneware cylinder. Inside turquoise stoneware glaze. Outside crystalline yellow/green with duck egg raku over bottom half which has created a cloudy, lichen-esque pattern. Red iron oxide details. The turquoise stoneware glaze turned an almost emerald green and had a bubbled texture.

20170213_162842-567x800

20170213_162345-800x586
4 layers Transparent green stoneware glaze on RsT

 

20170213_162356-800x611-2
Chun type green over crystalline yellow/green

Update: The kiln should have fired for another hour because the cone fell over instead of bending so didn’t reach optimum temperature. The glazes have been underfired which may explain why they didn’t flow much and why the raku blue was so vibrant.