Friday, 23 December 2011

Merry Christmas!!

To all who celebrate it, I wish you a happy and peaceful Christmas and New Year. I hope all the artists out there have an enjoyable, creative and successful 2012!

Turkey, Christmas pudding, mince pies, chocolates, wine, beer....sigh, the diet will have to wait again until next year. Shame..

Friday, 16 December 2011

Global warming? Really??

Somehow, the thought of plunging my hands into buckets of water and throwing clay doesn't seem very appealing today..

Looks like we might be in for the same kind of winter we had last year and the year before.. absolutely freezing!

Thursday, 8 December 2011

John Leach, Potter.

I've just been watching a very pleasant interview with John Leach, the Potter. For anyone who would like an introduction to the world of handmade ceramics, it offers an interesting overview of life in a traditional pottery workshop. John Leach has a fair amount of experience, having been a potter for over fifty years!

Wednesday, 7 December 2011

More interesting glaze results!

I fired the electric kiln to cone 9 this week and some exciting pots and test pieces have emerged! This large tea bowl was decorated mainly with a red clay and iron oxide slip..the thinner lines were made using the black slip (which contains red clay, manganese dioxide, cobalt oxide, red iron oxide and Masons black stain).

The glaze is a traditional shino comprising mostly of nepheline syenite and it has bubbled vigorously on the outside. What's really interesting is that the same glaze hasn't produced this volcanic effect on the inside, or over the bare clay.

Large tea bowl, fired to cone 9

Large tea bowl, fired to cone 9

The bubbling seems to be caused by a combination of slightly thicker glaze application and higher temperature, but I suspect that the main reason is decomposition of the red iron oxide which releases oxygen and this has to try and escape from the glaze. Red iron oxide Fe2O3 lets go of an oxygen atom at around 2250 F (1232 centigrade) and becomes black iron oxide (FeO). Where the glaze is thicker, and there is a heavier application of slip, I am guessing that the oxygen can't escape the glaze layer so easily and produces bubbles and craters.

In the case of this tea bowl, the bubbles have produced a smooth, sugar-fosted kind of texture, which is very pleasantly tactile, so on the whole, I'm pretty happy with it.

Here are two lidded jars, decorated in a similar way:

Lidded jar, approx. 6 inches tall

Lidded jar, approx. 5 inches tall

I also brushed on more of the orange matt, calcium glaze onto a previously fired vase and it came out anything but matt! It was fired in the saggar under quite heavy reduction and the titanium dioxide has created some wonderful glaze effects:

Carved "waterfall" vase, approx 5 inches tall

Carved "waterfall" vase, approx. 5 inches tall

The only problem I'm experiencing with this glaze is some bubbling and pinholing. Really not sure why this is happening on some pieces and not on others..perhaps the bisque surface wasn't completely free of dust and dirt etc, as some of the ware has been sitting around for a while.

The test piece below was coated with a stoneware matt transparent glaze, and the decoration brushed on top with a mix of 50/50 red iron oxide and yellow iron oxide. It's quite easy to paint onto this unfired glaze, but there's always a danger of disturbing or smudging the surface..I much prefer working directly onto bisqued clay. The glaze is very unobtrusive and just enhances the natural colour of the clay slightly. I rather like the combination of muted colours here.

Red & yellow iron oxide over matt transparent glaze

The next trial pieces are interesting where I tried out a Japanese recipe for nami jiro glaze. This is a very simple recipe consisting of 50 ball clay, 50 wood ash and 5 to 20% kaolin (according to Lee Love, the proportion of kaolin is varied depending on where the piece is to be placed in the kiln. Thank you, Lee, for sharing this information!). I used washed oak ash and 5% kaolin over a clay body which is 50% original raku and 50% Earthstone Original stoneware. Where raw ash is used, I'm thinking that such a high dosage must make the glaze slop pretty caustic, so care should be taken in handling.

Black slip & red/yellow iron oxide under nami jiro

The trial on the left shows nami jiro over black slip, with the slip and glaze applied to bone-dry clay. This glaze has produced a pleasant oatmealy colour on the clay body, with a very matt finish. On the black slip itself it's created a slight sheen. Used on its own, I would prefer the glaze to be a little glossier, which could no doubt be achieved by adding a bit more potash feldspar to the mix. But combined with a glossy oribe glaze in contrasting areas of a pot, it could work really well. The brushwork has stayed clear and dense, which is what I was hoping to achieve.

The piece on the right is the same glaze but the brushwork was done with 50/50 red iron oxide and yellow iron oxide. It's clear that the yellow iron oxide is a weaker pigment (as it contains some clay) and the decoration has faded somewhat, especially at the top where the tile was double-dipped.

Lastly, I re-tested the Leach 4321 tin glaze, but added more tin oxide, which takes the tin oxide content from 2% to around 3.5 to 4%. The test tile has come out quite nicely, but I was pretty amazed to see that the glaze was glossy and completely clear! It's really gobbled up the red, black and yellow iron oxide decoration (on the other side to the one shown), but the black slip has stayed fairly well defined..I think because only the 15% black stain has survived. So I could probably get the same effect by just adding Mason's black stain to a kaolin/ball clay slip.

Black slip under Leach 4321 + 3.5% tin oxide

Why has all the tin oxide disappeared completely? I'm not sure, but I came across something online today which says that the Leach 4321 glaze is a cone 8 recipe. So maybe taking it to cone 9 is over firing and makes the tin oxide act more as a flux instead of an opacifier. Food for thought...

NB. All the test pieces and the large tea bowl were fired in oxidation.

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

Saturday, 26 November 2011

Some experiments with black underglaze

Most of the glazes I applied for the last firing were successful, but I was a little disappointed with the black slip I used for the underglaze decoration (brushed onto bisqued clay). I tried out several different clear glazes, glossy and matt, and most of them "ate" the black slip to some extent. I was hoping that by adding 15% Mason's black stain to the slip recipe I was already using, I would obtain a denser, more solid, line. The colour certainly turned out much blacker, but on some pieces the decoration was still too faded under the glaze. Of course, it's possible that the slip was slightly too diluted..

One surprise was that the Leach 4321 glaze with 2% tin oxide came out almost clear..just slightly milky in the thicker areas, but the underglaze painting has remained reasonably well defined on this bottle-vase:

Bottle-vase. Approx 6 inches tall. Cone 9 oxidation.

I read yesterday that on traditional oribe ware, Japanese potters paint brown iron oxide (a kind of burnt umber? We can't get brown iron oxide here) on top of a very thin transparent glaze, and that this glaze is made by adding a little wood ash glaze to feldspar. Unfortunately, I don't yet have a recipe, but perhaps painting onto the glaze helps prevent it fusing and being absorbed. But I find it hard to believe that all oribe work is done this way, because I've watched Goro Suzuki painting directly onto raw clay..also, many of the pictures I've seen on the web seem to show the iron decoration under patches of thicker, cloudy glaze. If anyone can enlighten me as to the exact process, please drop me a line! Painting directly onto unfired glaze would also be problematic if the glaze surface is loose and powdery (as it is with Hamada clear glaze), which may explain why they use a form of feldspar to help harden the surface. Having said that, I imagine that most oribe potters will be raw glazing (applying glaze to leatherhard work), which could make a huge difference to the qualities of the glaze surface.

Most clear glaze recipes I come across, contain some form of calcium oxide, which in large quantities can have a bleaching effect on iron oxide. So, I'm guessing that oribe potters use a glaze which avoids using whiting (calcium carbonate), for example.

The bottle vase shown below was glazed with a low-clay shino, and the decoration has stayed very clear and solid under the glaze, with no fuzzy edges. I was really pleased with the finish achieved here and will be using this combination again.

Bottle-vase, approx 3 inches tall. Cone 9 oxidation.

Bottle-vase, approx 3 inches tall. Cone 9 oxidation

Another approach might be to spray wood ash onto the bisqued clay, before decorating with a gas kiln, it gives an attractive flashing effect on the clay, but I don't know if it would work in an electric or whether it would harm the elements (in the same way that soda ash does).

The next step is to try applying the clear glaze a little thinner and see how different iron pigments behave on top. (Just thinking out loud..any craters and pinholes in the glaze surface are also not going to help with fine brushwork..). I'll mix up a few combinations of yellow, red and black iron oxides and also combine them with a clay slip to see how it affects brushability etc.

And tomorrow, I really must tidy up the studio a little..experimenting with new glazes makes plenty of mess!

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

Monday, 21 November 2011

Frustratingly frothy glazes!

The last few days have been fun and games, trying to make larger batches of the Hamada and Leach clear glazes, the main problem being that both glazes contain little or no clay. The Hamada glaze has no clay at all and consists mainly of feldspar, which means it settles out incredibly needs a helping of bentonite and epsom salts (many thanks to John Britt for his helpful advice on that!) to stop it deflocculating into an immovable lump at the bottom of the bucket. The Leach glaze contains only 10% china's basically the Hamada glaze with the addition of a little clay.

Another problem with these glazes is that after mixing with water, they froth up tremendously, so when you dip a pot in it, the glaze surface is left covered in bubbles and craters, large and small. I waited a full 24 hours for the bubbles in the Hamada glaze to subside, but it was just as bad the next day. I was thinking that it might be the rough surface of the plastic container which was causing the frothing, so i transferred it to a glass bowl and this seemed to calm things down a bit. The strange thing is that by day three, both glazes had settled down and didn't bubble up nearly as much when stirred..why this improvement happens I have no idea, but the lesson is to try to mix up glazes several days before I need to use them.

And the final issue I faced was heavy drips and runs forming on the rims of pots after dipping them. With a clear glaze this can cause problems because thicker areas may fire white or milky rather than clear. After glazing a couple of pots, I suddenly remembered that I'd bisqued them at a slightly lower temperature than the previous batch (1020 rather than 1050 degrees C) and it's surprising how much difference that makes to the speed of water absorption. Effectively, the glaze was now too thick for this lower temperature bisque ware, so the drips were drying before they had chance to run off the edges.  It's very easy to forget to take into account one of the factors which affect how the glaze behaves..not very exciting, but I'll list them here mainly for my own benefit, so I don't forget next time:

1. The thickness/density of the glaze slop. For years I tried to judge this by eye but it's much less risky to measure it with a hydrometer (or weigh the glaze exactly, relative to an equal volume of water).

2. The temperature of the bisque firing.

3. The thickness of the pot walls. The heavier the pot, the more glaze it will suck up. Glazing the inside of a thin pot will then affect the amount of glaze the outside surface can absorb. One may need to wait a day between glazing the inside and outside of a very thin-walled vessel.

4. The amount of time the pot is dipped for. I usually dip my pots for between 3 and 8 seconds, depending on what thickness I'm aiming for.

5. If gums like CMC have been added to aid suspension or glaze hardness, they may also affect speed of glaze drying and how much glaze is absorbed by the clay.

Anyway, by early evening today, I'd managed to glaze a number of pieces reasonably well..and the proof of the pudding will be in the firing tomorrow!

Never give up, the best is yet to come! 

Sunday, 13 November 2011

This week's glaze results

This week's firing produced mixed results. Several pieces were fired in the saggar but only one (a small cup I had glazed for the previous firing but couldn't fit in the saggar) came out with the finish I was looking for:

Cup with orange matt glaze, fired to cone 8
 The other pieces I prepared for this firing came out way too dark, basically because the glaze was applied too thinly:

I have a feeling I may have added a little extra water to the glaze slop, thinking it would evaporate before I next used it, since the bucket lid isn't airtight. I'd also mixed in some CMC  to help with glaze suspension ( carboxymethylcellulose is a kind of organic glue ) and this appears to have rotted as it now stinks dreadfully, like no glaze I've ever experienced! Smells just like a stagnant pond! I've since learned that a side effect of CMC is that glaze dries alot slower, which I assume means that more glaze pours off the pot after you dip it. Normally, the first layer of a glaze will dry almost instantly on the bisqued surface. I think in future I will stick to bentonite for glaze suspension, not least because it doesn't go off.

Here are some of the test pieces I put in as well:

Test pieces, fired to cone 8 in oxidation
Whenever I take trial pieces out of the kiln, they usually raise another half dozen questions I would like to have answered. I'm trying to achieve a dark (preferably black) slip or engobe decoration under transparent and semi-transparent glazes at high stoneware temperatures (cones 8 to 10). The Hamada clear glaze on the right is interesting in as far as the black lines have stayed very black (which is odd, since it's absorbed the iron oxide from the background slip, which was originally orange). The other two tests were glazed with a mixture of Hamada and Leach clear glazes with a little tin oxide added. This glaze formulation was done by rule of thumb, not very scientific, but I was more interested in the effect on the slips under the tin glaze. For the middle one, I used an iron-rich clay body (a 50/50 raku and terracotta mix) and on this piece the decoration has come out somewhat darker than on the test on the left (a lighter clay body). The tin oxide in the glaze also gives the black slip a bluish tinge, with the result looking a bit like cobalt decoration on 18th Century delftware.

The lidded pot below was simply coated with two layers of black slip-glaze and it came out perfect, but another small vase blistered in several places. Based on previous firings, I had hoped that this black slip-glaze was very reliable, but it appears that more than one coat and there is a chance of peeling. It might be worth making it with a little flux added to see if it makes any difference to adhesion.

Lidded vessel approx. 3 inches tall. Fired in oxidation.

Never give up, the best is yet to come!

Saturday, 5 November 2011

Eric Knoche's wood-fired ceramics

Yesterday I became an admirer of Eric Knoche's functional and sculptural ceramics. His work is partly influenced by the Japanese ceramic tradition, and he was fortunate enough to spend several months working as an apprentice to Japanese potter and Living National Treasure, Isezaki Jun. A video was produced, giving an overview of his time in Japan, and providing a fascinating insight into the daily working practises of a Bizen pottery workshop.  It demonstrates the arduous processes involved in collecting and preparing the clay, and the quiet, steady discipline required to produce work of the highest standard.   (the password required to access the video is "woodfire")

A gallery of Eric Knoche's work may be viewed here:

Friday, 4 November 2011

Jim Malone, potter

I thoroughly enjoyed this wonderful film about Jim Malone, the potter, made by the Goldmark Gallery, Uppingham. Jim's philosophy is that "the best pots are born and not made".



Goldmark Gallery:

Slideshow of 2011 exhibition:

Nice weather for the time of year!

Autumn is upon us, but the weather this has been rather nice this week. That is to say, we've had some clear skies and it's not freezing cold, and there's alot to be said for that when the only heating you have in the studio is a small electric fan heater! All the bright sunshine we've been having seems to have stimulated the right side of my brain, and I'm having a creative spurt just now. I'm busy developing some new ideas for vessels in various shapes and sizes, mostly with lids. I've not made many pots with lids before, and I know that the problems of firing increase exponentially due to problem of glazes sticking and lids warping and so on. Partly for this reason, I'm going to start by low firing most of the lidded vessels I'm making at the moment, and use slips and terra sigillata to decorate them. I think a low-fired finish will suit many of the forms I'm throwing at the moment, so I'm happy to go down that road.

This carved pot on the other hand, will probably need to be fired to stoneware:

The vessel was thrown as a closed form, then carved once it became leatherhard (which takes over a week this time of year as closed forms take longer to dry out of course). I didn't really consider the pot's function as I was making it..but perhaps it would make a nice tea caddy.

Then there is the bottle sculpture.. :

This is one of those pieces that comes about by complete accident. I'd thrown a bottle on the wheel and didn't much like the form or the heavy weight of it, so decided I'd cut it in half to check the wall thickness and then chuck it in the recycle bucket. Once I'd chopped it in two, I noticed how much the halves resembled two figures, sitting opposite each other, especially when I squeezed the middle and the necks kind of leaned back a little. Anyway, I joined them back together with slip, and this was the's giving me some ideas for other similar pieces I could make, so I thought I'd make a note of it here.

Wednesday, 2 November 2011

The ceramic work of Jenny Mendes

Jenny Mendes is a hugely talented ceramic artist and an expert in the use of terra sigillata. Her work is made from terracotta clay and she applies an enormous variety of coloured slips to create fantastical and intriguing designs. I can highly recommend a wander through her Etsy online store, where she is displaying over 250 of her imaginative pieces.

Sunday, 30 October 2011

The plain of jars, Laos

The plain of jars, is a megalithic archaeological site in Laos. Scattered across the landscape are dozens of what are thought to be funerary jars fashioned from solid blocks of sandstone. They date from the iron age, perhaps 500 BC to 200 AD. It is thought that the lids were often made of perishable material as relatively few have been found.

Image linked from: )

Wednesday, 19 October 2011

The art of Michał Puszczyński

I am fascinated by the sculptural work of Polish artist, Michał Puszczyński. His work is deeply connected to nature and the cycles of birth, growth, procreation and death. Recent installations involve the use of raw clay, water and time-lapse photography to record processes of erosion and decay:

His ceramic sculptures are usually fired in traditional wood-fired kilns such as the Korean Tongama. More of his incredible work can be seen here:

Sunday, 9 October 2011

Lidded vessels

Just lately, I've been trying to find a way to make lidded vessels in one piece, so that the lid can be cut out from the solid form, rather than made separately. Ideally I would like the freedom to carve the form, before I fashion the lid. The problem being that, if the form is solid, it's very difficult to gauge the thickness of the clay whilst carving.

The pieces shown below were made using two different methods. A couple were thrown on the wheel as cylinders and then turned over and the base added as a disc of clay. I have to wait and see whether the joins will split in the biscuit firing..I hope not, as it was added when the clay was fresh off the wheel and soaking wet, but you never know. Clay has a way of punishing any slight weaknesses or stresses left in the vessel's structure..and the higher you fire, the wider any cracks become!

The piece back right and the two very small ones were thrown as solid forms, then allowed to dry to leather hard before carving and creating the lid.

I like the larger cylindrical form with the square lid was inspired by images of Pyxides (boxes) made by the Grotta-Pelos culture (c. 3200 to 2800 BC) in the Cyclades.

Early, cycladic cylindrical pyxis with lid

Early cycladic, cylindrical pyxis

Images borrowed from:

Tuesday, 4 October 2011

Ancient pottery can teach us a thing or two

I love looking at ancient pottery. At first glance, many of the pieces may appear quite primitive and crude, but I find great beauty in their simple and functional designs. No doubt these are pots which were produced under difficult circumstances, using less than ideal materials, and yet they were often elaborately decorated..the potters took time and care to make their work attractive as well as useful. The fact that many of these pieces have survived for thousands of years, buried in the earth, is testament to the skill and determination of the craftspeople who created them.

One design I'm very drawn to is the bronze-age beaker vessel:

Bronze age beaker
 Image borrowed from:

This form is incredibly beautiful, yet highly functional too. The flared rim created an angled lip which is comfortable to drink from and easy to grip with one hand. The rounded base would have been pleasant to hold in both hands as well as being suited to uneven, earth floors; when half full of liquid, it would be quite difficult to knock over.

The colours of these ancient works of art are also wonderful. There are the burnt hues created when the iron-rich clay was fired, probably in an open bonfire, the chips and scratches from everyday use..and then the earthy patina acquired from being in the ground for many hundreds of years.

Thursday, 29 September 2011

Autumn haiku

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

J.Andrew Lockhart

Wednesday, 28 September 2011

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 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'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! ;)'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'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!

Sunday, 25 September 2011

Contemporary, Japanese ceramics at e-Yakimono

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

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:

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.

Tuesday, 20 September 2011

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:

and here:

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!

Saturday, 17 September 2011

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 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

Wednesday, 14 September 2011

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 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...

Sunday, 11 September 2011

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/ 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)
4% manganese dioxide
4% iron oxide
2% cobalt oxide

Bowl with black slip glaze and matt ochre ash glaze inside

Saturday, 10 September 2011

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 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

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

Thursday, 1 September 2011

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 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 can see that the terra sig is semi-opaque on this sample, but it looks highly promising!


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

Wednesday, 31 August 2011

The ups and down of the potter's life

Today I was feeling bright-eyed and optimistic as I opened the kiln. Most of the glazes I'd used at least once before and I thought I'd learned the lessons from previous trials and errors..

But, as is so often the way, some pieces came out looking great, some were indifferent and one or two were a bit of a disaster. Murphy's law dictated that the carved piece I placed in the saggar, which I wanted to come out best, was one of the slight disasters! I knew that my satin-matt, orange glaze could be a bit runny, probably because heavy reduction in the saggar was causing the metal oxides in the glaze to flux more than normal. But I really didn't expect the glaze to run right off the bottom of the pot and weld the wadding to the base! Fortunately, I could remove it from the kiln shelf, so it might be rescued with some judicious use of the Dremel grinding tool. The other minor defect was some pinholing on a couple of pieces, which I suspect may be due to the thicker clay walls releasing more gases during the firing..I'm not sure how I can get round that problem, apart from applying the glaze more thinly, which may (I say, may, I don't really you?) allow gases to escape and any bubbles to heal over more easily. I have a feeling that I may have over-fired everything a little too, as I soaked the kiln for almost an extra half an hour. That was because cone 8 didn't seem to be fully over, and I was concerned that the glazes may not have fully matured..ah, hindsight is a wonderful thing..if only..

Having said all that, I was really delighted with the glaze finish on several pieces..the orange satin-matt glaze looks like being a real winner, I just need to understand how best to apply it. The upside of the glaze running alot was that it created some beautiful rust-coloured "waterfalls", pouring over and off the carved ledges. I was also very happy with the small jug, shown below, with an oak-ash ochre matt glaze on the has a different, slightly glossier ash glaze applied to the inside, which has also produced a nice orange blush in parts.

Well, at the end of the day, it was an interesting firing and I feel I learned a few more things. And that's what ceramics is all about; taking small steps each time, learning from the mishaps and mistakes, and gradually moving forward. Making pottery certainly teaches you about patience and stoicism..but, despite the downs, one should never give up..the best is yet to come!

Glaze run-off under base of pot below

Carved vessel with satin-matt glaze. Reduction fired.

Carved vessel. Approx 2.5 inches tall.

Jug with matt ash glaze, approx. 5 inches tall.

Monday, 22 August 2011

Matt ash glaze: unpredictable and intriguing!

It's been a nice, warm sunny day today..just a few clouds in the sky and no rain at all for a change! So it was a beautiful morning to open the kiln and end up smiling at some of the interesting pieces which came out.
Most of the pots I put in yesterday were glazed with the same oak-ash, matt glaze I used on the little sake cup last time. I put a few pots inside the saggar with a little charcoal and the rest on the top shelf so they would fire in an oxidised or neutral atmosphere.

I find this glaze really fascinating, as the finish seems to be affected by a number of different factors. As usual, glaze thickness is critical and I discovered that one brushed-on coat simply isn't enough..that piece came out rather dull and patchy in appearance with barely any yellow in the surface, almost all dark reds and browns. Brushmarks were also clearly visible in places. What was interesting though, is that some pieces ended up being quite similar in appearance even though one was fired in oxidation and the other in reduction in the saggar. Another critical factor seems to be heat work on the piece and whether they are directly exposed to the fumes from the charcoal in the saggar. The more heat and fumes, the darker the glaze seems to get, to the point where it turns quite black. Most pieces have a yellow-brown-black mottled appearance, but one espresso cup has a really deep red-purple hue and the yellow areas have hints of green in them too (please see the first photo below).

All in all, this glaze is fairly unpredictable, but in a good way..unlike some glazes where they are unpredictable and their revelation is invariably accompanied by a deep sigh of tragic disappointment. I'm pleased with most of the pieces I pulled from the kiln today, and I'm happy that this glaze recipe provides a wonderful starting point for further experiments. Next time I intend to try layering a satin-matt calcium glaze over this ash glaze and see what occurs..I can't wait!

Espresso cup with matt ash glaze. Reduction firing

Oil pourer with matt oak-ash glaze. Approx 3 inches tall
Oxidation firing

Vinegar shaker with matt oak-ash glaze. Approx 3 inches long.
Oxidation firing.

Bowl with matt oak-ash glaze. Approx 3 inches tall.
Oxidation firing.

Espresso cup with matt oak-ash glaze. Oxidation firing