Autumn haiku





thinking of you
today, only today,
but no words-
leaves whisper my story
as they fall softly

by

J.Andrew Lockhart

(borrowed from: http://autumnhaiku2008.blogspot.com/ )

High-manganese glazes

The latest firing was an opportunity to fire a batch of pieces with glazes high in manganese dioxide. I have to say, I am reluctant to fire with manganese as there are health hazards to consider..it does volatize at high temperatures and the fumes can be toxic if inhaled. But I figure if I keep everything well ventilated and only fire with it very occasionally, the risks will be minimised..

Anyway, I was pleased with most of the work which came out this time. The manganese glaze is a very simple recipe (23% china clay & 77% manganese dioxide) which should, in theory, create a kind of grey-black, pewter-metallic finish at 1240 to 1260 degrees C, in an oxidised atmosphere. Given that I only fired to cone 6 with a 15 minute soak, I was surprised that the stoneware pieces came out very shiny..the glaze had even begun to run, even at this relatively low temperature (low for stoneware, at least).

This sculptural piece shows how glossy the glaze had become:

Sculpture, approx 5 inches long

A much more matt finish was achieved where I had brushed this glaze over an existing layer of black slip:

Sculpture, approx 4 inches tall

My electric kiln tends to fire very hot and often the temperature appears to have gone higher than the bent cones would suggest. Perhaps the rate of temperature increase is too high..it's difficult to tell, as I don't have a pyrometer with a digital read out.

Well, I think (or am guessing) this glaze works better over a black slip because the slip layer is melting slightly, allowing the glaze to fuse with the red clay beneath, which also contains extra red iron oxide, cobalt oxide and yet more manganese dioxide. Where there is no slip layer, it seems that the glaze simply melts over the stoneware body and begins to run. If there is a next time with this glaze, I'll fire a cone lower to cone 5 and see if that gives a less glossy finish.

This next piece was glazed with two types of manganese glaze, one of which has some iron ochre in it, giving a slightly reddish tinge:

Lidded vessel, approx 5 inches long

We're having a mini heat wave here at the moment (okay, 27 degrees C is boiling hot by our standards! ;) ..it's amazingly sunny for the time of year so the raw pots are drying out in hours rather than days. Yesterday, I was out most of the afternoon and came back to find several cups and bowls I threw a day or so before were already rock hard..too dry and crusty to trim the bases. Well, I don't mind..it's wonderful to see a bit of the summer which never really arrived earlier in the year. Outside, there is that lovely warm, damp smell of summer evenings..long may it continue!

Contemporary, Japanese ceramics at e-Yakimono

Much of my knowledge of Japanese ceramics has come from a single website, e-YAKIMONO.NET:


http://www.e-yakimono.net/html/whoiswho.html


The site is run by Robert Yellin who also hosts the Robert Yellin Yakimono Gallery in Mishima City (Japan). I've found it to be an invaluable mine of information about the history of ceramics in Japan, and about individual potters, their backgrounds, styles and philosophies of working. There are also clear explanations of various traditional terms used, such as the "koudai" or "kodai" which means footring (of a tea bowl). On this page, the Author explains the importance of the kodai to the overall design of a tea bowl and provides images of many different pieces, demonstrating how each potter gradually develops a refined and distinctive way of forming the footring:


http://www.e-yakimono.net/html/kodaik.html


Visit the e-Store section of the website, and you'll find an online gallery containing a vast repository of images of works for sale and an archive of sold pieces. The thing I really enjoy about this part of the site is that every ceramic piece has been photographed from multiple angles, so you can really get a good idea of how the pot would feel in the hands. Some of the pieces shown here are truly spectacular works of art and I am often left wishing I could have watched and learned from the artists as they created them.

Inspiration from Japan

I really love the work of many contemporary and traditional Japanese potters. I find the purity and integrity of their craftsmanship very inspiring.

Carved tea bowl. Unfired, raw clay.

This tea bowl I carved yesterday was influenced by a number of Japanese ceramicists, including Bizen artist, Kakurezaki Ryuichi. If you're interested, you can see a gallery showing a small selection of his work here:

http://www.geocities.jp/gallery_coco903/utuwa/bizen/kakurezaki/kakurezaki.htm

and here:

http://www4.ocn.ne.jp/~ranran/ran08_kakurezaki_suiki.html

I would like to learn more about the carving techniques and the specific tools they use in Japan, but it's very hard to find any detailed information online. Perhaps Japanese potters tend to closely guard their trade secrets, or only pass them onto their apprentices, I don't know..but if anyone out there is aware of any useful links or texts, please do share them with me!

Experimenting with terra sigillata once more

I thought I'd show a couple of pots from yesterday's firing. I wanted to find out whether terra sigillata would stay put when painted onto bisque-fired pieces, so I decided to try it out on three lidded boxes. I mixed a couple of grams of yellow iron oxide into some liquid, white terra sig. (no accurate measurements taken this time), and as you can see, it's come out light yellow in colour. Ideally, I would like it to have been more of a rusty orange, but I still like this result.

I'll have to wait a while to see if the coating of terra sig. will stay put as one of the boxes has already peeled, I think where the clay was way too smooth. I remember I had smoothed these pieces, almost to a shine, with my fingers and terra sig doesn't really like sticking to burnished surfaces. When I've used it in the past, I've noticed that a pot can look perfectly fine for a day or two, and then, maybe once the clay has contracted and expanded with temperature changes, it suddenly starts flaking. So, brushing onto bisqued ware hasn't eradicated the problem altogether, but there is a definite improvement..I just need to make sure I leave the clay surface fairly rough from now on.

These terra sig. pieces were fired to 1100 degrees C in a sealed saggar with a little charcoal, and I bisque fired a few other carved pots at the same time. I realise this is pretty high for a bisque firing but I want them take up less glaze, and this is one way to achieve that. The good news is that my carved pots came out perfectly..no cracking or splitting this time, thank goodness!

Interesting too, that the the box in the first photo is a deeper yellow, as the terra sig. was applied over a clay body containing more iron. The second piece was made from a lighter coloured clay body..a 50/50 mix of original raku and a pale stoneware clay.

Carved, lidded box. Approx 3 inches long

Carved, lidded box. Approx. 5 inches long

I've got the bisque-fired blues...

Yesterday was a bit of a downer to say the least. Several of the new pieces I had carved from solid blocks of clay cracked very badly in the biscuit firing..beyond hope of rescue in fact. I was really surprised and shocked, not to say dismayed, because they were some of the pieces on which I'd spent the longest time working and the ones I was most happy with in terms of the form. Why, I ask myself, is it so often the most pleasing pots which end up with the worst faults? On reflection, the answer to that, is probably that the most interesting pieces are often the ones which result from trying out new techniques, and pushing out into the unknown, as it were..and hence coming up against new problems which need solving.

The annoying thing is, I've employed this hollowing-out technique before on sculptural pieces with barely any problems. The French, grogged clay I've been using for the last couple of years, seemed to be very tolerant, very warp and crack resistant, even when the clay is left at different thicknesses. But this time, two of the vases split down the seams where the clay had been joined. Maybe the clay was too dry when I joined the two halves..or I'm wondering if I took the temperature up too quickly, given the thickness of the clay in one or two cases. I did put the kiln on a higher setting than normal during the final phase, trying to save some time, which was probably a big mistake and not one I'll repeat in a hurry. I suppose I was really pushing this clay to its' limits in terms of what it can withstand..and now I know it has its' limitations!

Hey ho, such is life with ceramics..you win some, you lose some. But, seriously, I do need to reconsider my clay body for this type of hand-built work, and probably formulate a more groggy, crank-like mix to avoid these minor tragedies in future. The other day, I did a firing test with a 50/50 original raku and grogged terracotta mix (the terracotta is earthenware clay and normally has a maturing temperature of only 1180 centigrade). It fired surprisingly well to cone 8 (over 1250 centigrade) with no bloating or sticking to the kiln shelf. But I did notice the test piece had shrunk tremendously, like to about half it's original raw-clay size, or so it seemed. I must do a scientific test to compare shrinkage with normal stoneware clay, and check my eyes aren't playing tricks. Anyway, this particular clay probably won't solve my cracking problem but it's an interesting possibility where I need a high-iron clay that will withstand a 1250 degree plus firing. It could be very useful for shino glazes, where an iron-bearing body would give a stronger, deeper fire colour.

Next I'm going to mix the raku clay and the French stoneware clay and see how resistant that is to cracking...

Black slip-glaze

Lately, I've been experimenting with various types of black slip and engobe for firing in oxidation. I'm really looking for one which will work well under a semi-transparent stoneware glaze, so I can develop some Japanese-style painted decoration on my pieces. This recipe actually looks quite effective on it's own as a black slip-glaze, when fired to cone 8/9..one advantage being that it brushes on to stoneware very easily, either at the leatherhard stage or after bisque firing. So far, it appears very reliable and doesn't peel off or crack. It creates a fairly matt surface, but has a very slight sheen to it as well. The small bowl pictured below was given two coats on the outside.

Black slip-glaze recipe:

Keuper red clay 100 (dry weight)

plus

4% manganese dioxide

4% iron oxide

2% cobalt oxide

Bowl with black slip glaze and matt ochre ash glaze inside

What could be more challenging than ceramics???

I'm sitting here this afternoon, contemplating which is more difficult...getting a pleasing glaze result from the kiln, or photographing my pots! Of all the things I have ever tried to photograph, ceramics come top of the list as the most awkward and frustrating. I won't go into the boring technical ins and outs but anyone who has tried, will know that achieving the ideal lighting conditions, color balance, focal depth, background etc. is much more challenging when it comes to photographing pottery. Many glazes, being semi-translucent and reflective, tend to look very different depending on the intensity, direction and quality of the light.

In the past, I've always taken pictures of my pots in natural light, but the last few times, the weather has been driving me crazy, with lots of passing clouds making the sun go in and out constantly. Sometimes, it's impossible to get the correct exposure and colour balance..for example, the blue pots below are actually more of a light lavender-purple, but I simply couldn't get the exact hue, even after tweaking the images in Photoshop. I know I'm probably being too much of a perfectionist, but there seems little point showing people your pots online, if the glaze colours don't reflect reality! In short, I've realised I need a proper studio set up with controlled lighting to do the job properly. Time to raid the penny jar again..

Well, I took these shots this morning, having pulled another load of pots from my electric kiln. I do like these pieces and glaze finish is pretty good, but I'm still not entirely satisfied with this blue-lavender glaze..it doesn't matter how thickly I put it on, I'm still not getting enough of the mauve/lavender speckling, which I think adds more interest to the surface. I looked again at the original test piece today and noticed that the clay is a bit darker than the clay used in these pots..maybe I accidentally used a reclaimed, mixed body which had some red clay in there, and hence more iron oxide.

Satin-matt mauve glaze:

Potash feldspar 45

Dolomite 22

Quartz 16

Zirconium silicate 11

China clay 6

+ Cobalt oxide 2

( Source: The Glaze Book by Stephen Murfitt )

I'm quite pleased with the matt ochre ash glazes, which came out pretty much as expected, although with a slightly rougher texture than before, as this time the body is a white stoneware-raku mix (50/50) body which is very coarse. These pieces also had some underglaze decoration in the form of a red clay slip with 5% red iron oxide added to it. You can just see the darker stripes and dots showing through on the beer mug photo. I imagine this very earthy, rustic finish won't be to everyone's taste, but I really like it. I think the variegated surface gives the pots a rather ancient look too, as if they've been buried in the ground for hundreds of years..

What do you think? I'm always interested to hear people's reactions to my work, so please feel free to leave a comment!

Carved vessels with satin-matt mauve glaze. Fired to cone 8/9

Beer mug. Matt ochre ash glaze with slip decoration.

Tea bowl. Matt ochre ash glaze with slip decoration

Tea bowl. Matt ochre ash glaze with slip decoration

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Never give up..the best is yet to come!

A handful of test pieces

Please click on the image for a larger view!

The latest electric firing yielded some interesting test results! From left to right:

Test 1: This was a matt orange calcium  glaze applied over matt ash ochre glaze, fired in oxidation (only the top half shows the glaze overlaid). The result is a wonderfully smooth surface, almost like bone or tooth enamel. The colour is hard to describe..a kind of light greeny-yellowy-tan. The titanium and iron oxides have also run into the incised pattern, created deeper, mottled areas of pale orange-brown and tan. The colours are muted, but on the right piece it could work really well, I think.

Test 2: This is the matt ochre ash glaze again, but this time applied over a red slip. The red slip is Keuper red clay plus 5% RIO. The result is much,  much darker, and richer than the same glaze laid over iron-bearing stoneware clay. This was fired in oxidation..in reduction it would almost certainly come out completely black or very dark purple.

Test 3: Now this was interesting! Fired in reduction in a saggar,  this is the matt ochre glaze, but with the recipe tweaked somewhat.

I removed the iron ochre and replaced the koalin with Keuper red clay. The outcome couldn't be more different! The red clay has become as a much more active flux, and the result is more like a traditional ash glaze, with plenty of green glassy runs. I have read that calcium has a bleaching effect on iron and this seems to be happening here as it did on this piece below, where I overlaid a matt calcium tan glaze over the matt ochre ash glaze:

Carved vessel. Reduction firing.

Test 4: Another interesting trial piece! Some time ago I was trying to get a smooth terra sigillata finish by applying it to bone-dry greenware. I was having quite a few problems with it flaking off or peeling. It was a recipe by Anne Floche and really designed I think, for application to earthenware clays. I was using it on stoneware clays, and I suspect the shrinkage rate of the stoneware is lower than the terra sig when biscuit fired, hence the flaking off. The other day it occurred to me to try brushing the same recipe onto a pre-bisqued trial piece and then firing it to high stoneware. Miracle of miracles, it stayed on and with barely any cracking or peeling!! I need to test this further, perhaps with a slightly thicker application..you can see that the terra sig is semi-opaque on this sample, but it looks highly promising!

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Never give up..the best is yet to come!