The name, “Out of the Fire”, might seem a bit strange for an exhibition of pots that were fired in an electric kiln, however many of these had a further firing to around 850 – 900 Celsius in which I dripped cooking oil into the kiln to form, what potters call, a “reduction” atmosphere. The oil certainly produced fire, and a goodly amount of smoke, and carbon monoxide, which all had a marvelous transforming effect on the pots!
I have difficulty thinking of names and titles for the things that I make. The act of making a pot on a wheel is a non-verbal process, I have an inner need to express a form, and do so through my hands. Naming, pricing, explaining, all those “ing” words, bring me little joy! So I hope you will excuse the absence of titles, and try to discover the character of each pot, by looking at it!
About the Pots, sizes, prices, and purchasing information.
Dimensions are Height before Width and are in millimeters. Any inquiries about prices, availability, and purchasing work should be made to the Selwyn Gallery for the duration of the exhibition.
I have done my best to number the pots correctly to match the numbers on the gallery price list, however there could be errors so do check carefully with the gallery to make sure that you are both talking about the same pot!
The Selwyn Gallery is open 10 am - 4 pm Tuesday to Sunday (closed Mondays).
The exhibition is from 6 November to 4 December 2015.
The Selwyn Gallery is located on the Main Street of Darfield, which is about 35 km West from the outskirts of Christchurch, NZ on State Highway 73.
17 South Terrace
Phone 03 318 8702
1) 170 x 150 mm. Porcelain, fired in oxidation. This lidded jar has cobalt, copper, and a trace of iron in the glaze. I was pleased to be able to do a crystalline glazed pot with a lid, as such glazes are very fluid and hard to control and it is all too easy to end up with a lid stuck to the pot!
2) 184 x 158 mm. Porcelain, fired in oxidation. White crystals on a white background, same glaze as vase #17, but without the oil drip firing.
3) 160 x 165 mm. Porcelain, fired in oxidation. This lidded jar has manganese and copper for colouring. The two metals together often create a mirror glaze.
4) 197 x 134 mm. Porcelain, fired in oxidation. In this vase, and vase #5, I was exploring form. I really wanted to find a good shape for the crystals to look their best.
5) 188 x 127 mm. Porcelain, fired in oxidation. This is another with titanium dioxide and a little rutile. The rutile gives the golden colouring to the crystals. The crystals have pale growth rings in them that I put there by sharply dropping the kiln temperature by 40 degrees and then raising it again as the crystals were growing.
6) 221 x 134 mm. Porcelain, fired in oxidation and in reduction. This was a similar glaze to vase #5, but a shade or two darker with slightly more rutile. I re fired this with oil drip reduction and got this strange and interesting result, that makes me think of Mars!
7) 203 x 190 mm. White Stoneware, fired in oxidation. The colour in this crystalline glaze comes from titanium dioxide and rutile (which is titanium with impurities). I have never had those interesting red outlines to crystals in a glaze before or since!
8) 143 x 134 mm. White stoneware, twice fired in oxidation. A similar glaze to #9, but probably no cobalt or copper.
9) 125 x 138 mm. White stoneware, twice fired in oxidation. There is iron, manganese, a little copper and perhaps some cobalt in this glaze, but I can't quite remember! I did give this and its friend #8 two glaze firings each. This gives a very different look to the crystals, which often are quite small when they form for a second time, and very detailed. I call them bonsai crystals!
10) 177 x 133 mm. Porcelain, fired in oxidation. This vase is coloured with manganese and copper oxide, and is similar to lidded jar #3 in that, however the crystals developed very differently.
11) 248 x 156 mm. Porcelain, fired in oxidation and in reduction. Here the moment is captured where the pot was changing from being a copper green to a copper red. You will get a good idea of the original colour of this pot from the green colour near the foot.
12) 190 x 158 mm. Porcelain, fired in oxidation. This has a very similar glaze to vase #13, but has no iron oxide in the glaze. Notice how the crystals are much larger in the absence of the iron. The two vases shared the same firing.
13) 259 x 188 mm. Porcelain, fired in oxidation. This has cobalt and copper for its colouring, and just a trace of iron oxide. If you look carefully you will see tiny iron crystals appearing as little reddish brown dots.
14) 198 x 130 mm. Porcelain, fired in oxidation. Copper oxide and a little iron oxide are the metals that colour this glaze. Slow cooling towards the end of the crystal growing period assists the crystals to form dark, cartoon-like, outlines where the copper is concentrated.
15) 220 x 150 mm. Porcelain, multiple firings in oxidation and reduction. This chalice shaped bowl has an iron spot glaze on the inside, and crystalline glaze on the outside. I remember giving this one two glaze firings and a further two oil drip firings.
16) 210 x 147 mm. Porcelain, fired in oxidation and in reduction. This was first a copper green pot with green crystals, but a further firing with oil drip reduction made the copper carbonate in the glaze start to form copper metal. The interesting grey colours are caused by carbon trapping in the glaze.
17) 182 x 152 mm. Porcelain, fired in oxidation and in reduction. The first glaze firing gave me white crystals on a white background, just the same as what you will see in on lidded jar #2. A further firing with the oil drip gave the green crystals and pale purple background.
18) 213 x 222 mm. Porcelain, fired in oxidation and in reduction. Green to red, just the way I like it! Another oil drip reduction firing.
19) 382 x 240 mm. Porcelain with stoneware base, fired in oxidation and in reduction. I was thinking of Greek Myths and Legends, Stately Homes, Ageing, and Autumn when I made this, but perhaps it is best not to know that! A copper green glaze given an extra oil drip firing with carbon trapping.
20) 557 x 204 mm. White stoneware, fired in oxidation. This tall vase has cobalt and manganese for colour. I read a scientific paper written in the 1940s that suggested a way of firing that would give blue centres to the crystals surrounded by an outer grey border… and it worked! Essentially the crystals are grown first at a fairly low temperature, then finished off much higher. The centres took 2 hours to grow, and the surrounding spiky grey was a further 3 hours.
21) 285 x 290 mm. Porcelain, fired in oxidation. I think I had copper, cobalt, manganese and a little iron oxide in this glaze. On the outside, the lower two thirds of the pot were glazed with a dark brown saturated iron glaze that I often use inside pots. The crystalline glaze ran over this outer glaze rather beautifully in the course of the firing.
22) 450 x 260 mm. White Stoneware, fired in oxidation and in reduction. This vase was white with rather glassy white crystals the first time around, but I fired it again and dripped cooking oil into my electric kiln. This trapped some carbon in the glaze, and helped give the pale green/grey background and soft grey detailing of the crystals.
There are different sorts of crystalline glazes, micro-crystalline, aventurine, and macro-crystalline. The crystalline glazes in this exhibition are all of the macro-crystalline variety.
Macro-crystalline glazes have silica, a flux or two to melt the silica at a sensible temperature (usually sodium is the main flux for this), and 20 – 30 percent zinc oxide. The crystals that form in the glaze are zinc silicate, similar to the mineral willemite (Zn2SiO4). Metal oxides such as copper, cobalt, iron, nickel and manganese, are used to colour the glaze.
The crystals form in the glaze over the course of the firing. The firings are much longer than a normal stoneware firing, usually 15 – 20 or more hours of precise firing before the kiln is switched off to cool.
The way that the kiln is fired largely determines the number of crystals that grow, their size, shape, and character. When firing crystalline glazes, the kiln is used as a creative tool.
Crystals grown at a higher temperature tend to be spiky, those formed at lower temperatures are much rounder, rather like a pansy flower. Abrupt changes in temperature whilst the crystals are growing can trigger growth rings in the crystals.
Crystalline glazing is a difficult and demanding process, with every firing being like a laboratory experiment. Glaze formulation, application, thickness, firing temperatures and times, even the clay that the pot is made of, affect the result. Such glazes are abnormally runny at high temperature, and provision has to be made to catch glaze that runs off the pot in the course of the firing. There is a high failure rate, and it is usual to have to throw away 50 percent of the pots. I usually can only fire between 4 to 6 pots in one firing, and am always very thankful if one of them turns out.