… the biaxial revealed nothing.
Ever since I’ve been after oil spot glazes I’ve been seeing images of spots that are out of the ordinary. Famously, this National Treasure bowl in Osaka
which is probably not a ‘true’ oil spot in the sense that the incredibly vivid spots were somehow seeded in or over the glaze and not generated naturally from within it.
But also this National Treasure:
Which is very probably a true oil spot.
Until recently I relegated such things to the realm of National Treasures. Things that I can safely ignore in the course of my daily potting life, even though I knew about a few people in China and Japan who have such glazes and fire them in lowly electric kilns. I think Kamada Koji does, at least, but I may be wrong.
Ithaca gave me a nice ride, trying to see where oil spots would take me. Driven by a comment in Daniel de Montmollin’s book about the essential similarity between iron red and oil spot glazes, I started exploring the largely uncharted seas between them.
I was also driven to some extent by interest in the above iridescent oil spots. A few metals iridesce naturally in glazes, chief among which is the lowly iron. Iron reds often have a sheen to them that is only apparent when you hold a pot in your hand and look at it in the light. So looking at iron was a natural direction and it yielded some results that I have yet to explore fully.
The other suspect is Manganese. Unlike iron though, manganese is highly toxic. Not in a fired glaze apparently – according to some sources, http://ceramicstoday.com/articles/080999.htm, the body doesn’t process non-organic manganese compounds in large amounts. But in inhalation of dust and chiefly, of firing fumes, it can create Parkinson-like symptoms. A clear deterrent for me. I had tried adding a few percent manganese to previous rounds of oil spots, but didn’t get much except for the same kind of behaviour that you can get from cobalt (blacker, bigger spots) so I abandoned that route.
Until now. Knowing that someone closer to home is making iridescent oil spots has awakened my interest again:
I had come across his blog before, in relation to his metallic manganese saturated glazes. So I deduced that manganese was the way to go. I started by trying out a few of his less scary manganese luster glazes (judged by the amount of time I have to spend in the presence of such highly toxic substances), both in oxidation and reduction. They were lustery as advertised. Over and under my existing oil spot glazes, of which I have quite a few, they were lustery but not spotty.
The other thing I did was take two of my existing oil spot bases and try adding in iron along one axis and manganese along the other. A tedious process known as a biaxial blend. What I got was a bit surprising. The traditional oil spot territory of 8-10% iron did not iridesce in the presence of manganese. Instead, the lower amounts of iron did, increasing with the manganese. But nothing that I would call spots.
The plot took a surprising turn, when it turned out I know someone who knows the writer of the blog above. ‘Know’ in the facebook, virtual sense. Apparently after I chatted with him about the subject he chatted with Matt about the subject. And the picture became clearer. I was apparently right to look at manganese, but not daring enough with the copious amounts that were needed.
There is another problem. Oil spots are ‘stiff’ glazes. They retain the spots because they are glazes that don’t move much, having a lot of glass formers and stabilizers relative to glass melters. Not stiff enough, you won’t get spots. Too stiff, you will get just unhealed bubbles and craters in the glaze, looking like a mini volcanic disaster. But manganese is a glass melter. Especially in such huge amounts. So my current bases, tweaked to melt at my firing range (cone 9+, or 10-, saving my kiln from weekly element changes) won’t be stiff enough to hold the spots even if there were any. Looking at Matt’s firing schedule, his firings are long and slow and hence reach cone 12 even though the final temperature is that of cone 10 only.
Where does that leave me?
With a few more biaxial blends to do, in order to figure out if I can stiffen the base just the right amount to hold spots on one hand, and not bubble on the other. And still trying to zero in on the combination of metals in the glaze – how much iron, manganese, cobalt and copper, and maybe vanadium. A multi dimensional space. As my mathematical friends know, there is no efficient way to conduct a search on such a space. So I will resort to drudgery, looking at the various planes that (don’t even) bisect the space.
Or relinquish the search. Now that I know how it’s done in principle, I am much less inclined to find those amazing glazes. My initial interest in oil spots was that they are spectacular glazes that are ‘liner glaze’ worthy – that I can handle safely, using normal safety precautions of dealing with glazes, and that will fire to a glaze that I would not hesitate to use on the food and drink bearing surfaces of my largely functional pots. But I shudder at the prospect of handling such toxic materials as manganese dioxide, vanadium pentoxide, etc, on a day to day basis in my studio, and I’m unsure about the toxicity of the final fired product.
Yes, there is more news of a less tentative kind. I have produced a number of acceptable oxidation reds, have started exploring neodymium oxide as a potential source of purples and grays, and my celadons are going strong and multiplying both in fired pots and also in kinds of glaze. I have also stumbled upon a new oil spot glaze that I like, doing a fun little experiment. Here it is:
It’s essentially a two ingredient glaze: 75 grams Alberta slip and 25 of petalite, adding just a bit (4 grams) of iron. Oh, and a few drops of darvan, which does nothing for the fired glaze but helps turn the jelly that is the alberta slip into something more liquid and usable. I also think that a bit less iron could work as well. My guess is 3%. Try it out!
I’ve been a lazy potter.
It’s been ages since I sat down with fifty test tiles and the tiny scales and weighed samples of fifty different variations on a glaze to put into the kiln.
There is more than one reason for this. Maybe too many of them. One is that I was away for almost a month, to see my brother, my sister, and my parents (in three different places). It was my first time seeing my nephew, who is even sweeter in real life than in the photos. I caught the tail end of a festival curated around women drummers in NYC as part of my sister’s submission for Frieze NY. And enjoyed a rare and welcome respite of health and normalcy with my parents in Israel. My father is back to work, and riding his bike again too.
I’ve also been hurled into glaze making, as opposed to testing, by my studio mate Ann, of Golem Designs fame. A day before I left I went into the studio to finish the handles on some mugs and pitchers, when Ann asked my if I had anything to glaze for a cone 10 firing.
“No, just four test bowls, why?”
“Because I NEED to fire and the kiln is half empty”
There is no greater sin in Pottery than firing a half empty kiln. So glaze the bowls. But I haven’t mixed the tests. So mix them, three different 1kg batches. Two recipes are on Insight Live (online) so I pull them out. The third is trickier. It’s a point between two test batches, so I calculate the right mix on a piece of paper and keep it just long enough to mix the batch before losing it.
And glaze my bowls. Using the heat gun, the microwave, and faith, to make the glaze stick to the outsides of the bowls as the saturated bisque is sweating moisture absorbed from glazing the insides.
All that in under two hours.
“You know Ann, I didn’t mean to glaze today. At all. just pull a few handles and go pack”
“Welcome to the Golem universe”.
So they’re glazed – but now I fly to NYC, to take the bus to Boston and see my nephew and his appendages, formerly known as my brother and my sister in law. It was the worst bus ride of my life, worse than buses in India. The bus crawled and took three hours to get from NYC to New Haven. The AC didn’t work. And worse – the WiFi didn’t work, which means that the photos of the Oil Spot tests are just beyond reach.
Until we stop at a strip mall, and I manage to tap into a chain restaurants WiFi. And see this
My bus trip improved immediately. But now I am facing a problem. I know one of the three. But am not sure which are the other two. The problem is, they don’t look anything like the test tiles. One would think I could write down which is which, but true to form I didn’t (“It will be obvious which is which”: famous last words).
Besides, there was the pesky patter of the recipe that I lost.
So here I am, trying to learn about the application and use of glazes I have only seen on test tiles.
Also, the Guild summer sale was coming up and I was pressed to glaze pots. Especially bowls, of which I didn’t have enough. I had made six noodle bowls before I left. The perfect solution was to make them test pots. So I did. But I also had a big spiral bowl, and I didn’t want to use it for testing. Instead I played it conservative and glazed it in an oil spot which I’d already tested – it’s one I considered a little pedestrian compared to the potential of the others, but at least it’s safe:
Seeing this one, I am reminded that oil spot glazes are very sensitive to thickness. The bigger spots are where I glazed thicker – where the application overlapped. I usually spray my glazes, but I decided to try to get away with just dipping, and while I don’t hate the result, I think it would have showcased the form much better with a more uniform application.
The last reason for this advanced stage of glaze testing, is that in the back of my mind, there looms the Monster. The Bowl. I need to trust a glaze as much as a glaze can be trusted to use it on the Bowl.
So I decided to sacrifice a few tea bowls to further testing.
Which means I made tea bowls. Off the hump. And trimmed deep feet on them. All of which is like being some other potter who just happens to make use of David’s body. I made them for Olivia, of Treasure Green tea store in Chinatown, and I actually meant them to be gaiwans. Some of them were not the right size or shape so they became bowls. Most of them were glazed in celadon and sent to the gas kiln, which I’ll fire tomorrow. But three were left behind, to go into Ann’s firing in our studio, unloaded a few hours ago:
They are even richer in real life, reflecting the different surfaces and colours as the light on them changes.
All I can say is, I think I’m getting somewhere.
In the hidden belly of my studio I’ve been working on the One Bowl.
(Noises. Tolkien rolling in his grave)
I fashioned it out of 20 lbs of porcelain.
It took a few tries – and the added joys of re wedging such a big amount of clay so you can thrown it again.
I found that it takes the perfect mood. A mood of quiet alertness. Endless sensitivity in your fingertips, combined with a total lack of fear. A focused, relaxed attitude – taking the time to breathe and regroup after each step.
The right consistency of clay – soft, but not floppy.
Lots of physical force.
A big wooden rib
A small wooden rib
Thierry Fouquet’s pipe
A metal rib
About 45 minutes.
Not to sound too new age – in order for the pot to be centered, I need to be centered. This used to be the case with 1lb mugs, a long time ago, but now I can make them in my sleep. Pushing the boundaries means there’s a high chance of failure, so you need to be On. It’s different from feeling a thrill.
After all that, there’s this:
And you let it be, go do something else. An exercise in self control. And then you come back and still don’t like the rim. In this case you can only open it more, to fit the curve. But this is where bowls die. The ‘one more pass with the rib’. My greed has killed a great many pots.
But if you’re careful, and focused, and had a cup of tea while letting the bowl stiffen up slightly, it works:
And then you clean up and go home. leave the bowl on the wheel – at this point any movement can cause it to collapse. the plastic batt I threw it on can hardly hold its weight without bucking, which will introduce an un-get-riddable-of wonk to the bowl which would end up very warped after the firing.
At this point it’s 56cm at the rim.
The following week is an exercise in meditation. There’s nothing I can do at the studio. My wheel is taken. I come the next day and the rim has stiffened up some. It’s 52cm now, not a surprise – bowls always close up a bit after they’re thrown.
In my considered judgement the rim will survive gentle contact with a physical object, so I drop a piece of light fabric, just on the rim, and go home.
The next day I undercut the bowl with a wire and drop a piece of plastic on the rim, leaving the bottom uncovered, to dry more.
The next day I do nothing and don’t come into the studio.
The next day is the big day: I undercut the bowl four times with a wire. Place my 21″ foam board batt on top of it, and flip it with the rim on the foamboard. Do it too soon and the whole thing will collapse. Too late and the rim will crack from the weight. I gently pry the throwing batt loose – it come off without warping the bottom. I cover the rim again and go home.
After two more days I come back to start trimming the bottom of the bowl – giving it its final shape. At first it’s soaking wet, but I’ve found that with these big bowls, you have to start trimming wet to kick start the drying of the rest of it. So I trim off about 1.5 lb of clay and go home.
I do the same over the next two days, The bottom gradually drying, the rim covered to stop it from drying too fast.
And then comes another moment of truth and self control.
How perfect is perfect. How light does light need to be. When do you say, this is good enough. I’ll let you live. I used to be a terrible perfectionist, and I still am, but looking at the bowl and seeing the small kinks that were left behind, the bulk of it, little points where the curve doesn’t look exactly the way I like it, I decide that it’s done, time to let it go, and let it live.
I take a piece of paper, and a board, and put them on the newly carved foot.
Unusually for me, I take more pictures with my phone.
I know myself, Ulysses unbound, ready to yield to the siren song of more trimming, ending in a dead pot.
I have to leave it alone for at least four days, until it’s too late to even think about touching it again.
So I turn off the lights
And walk out.
Unusually not about pottery or about “my kind” of music.
Ran into this song yesterday. The refrain (“It rains, and the wind blows” / “deep under the crags, far north in the mountains they play”) immediately reminded me of a certain place in the mountains where the wind always seems to blow cold rain at you.
It occurred to me that many of the ways we view nature-as-wild, nature-as-beautiful and nature-as-threatening (those of us who view it or love it) have roots in medieval north germanic tropes. It’s a thought I want to make a mental note of, especially as it relates to this ballad, and incredibly, I’ve decided to do it online.
Also note, if you read Norwegian, that I find the vid poster’s attitude to immigration utterly despicable. And to follow that thought, can those tropes be disentangled from the racist attitudes they got enmeshed with basically from the time they were transmitted to us in the mid 19th century. I have some vague hopes that have to do with First Nations and their struggle for their lands, cultures and for recognition of grave injustices done to them in the past and in the present. And how it all relates to adopting their (many) ways of viewing nature.
A lot to think about.
And in the “Ceterum Censeo Carthaginem delendam esse” department: check out my new oil spots and celadons on my etsy page!
No, it is not a new environmentalist party. It is a measure of how strong a clay body is before it’s fired – in particular in the bone dry state. And the reason this is relevant? Oh, a certain 7lb bowl that was 15.5″ yesterday, 14.5″ today.
Vancouver is not known for sunshine. But today was an incredible spring day. Plum blossoms everywhere, green grass, white mountains, clean air, and yellow, warm sunshine. And so, after flipping the bowl I made yesterday, I put it out! in the sun! to dry! so I can trim it.
I worked on finishing my six individual teapot, like this one:
that I threw yesterday, occasionally checking on the bowl. After I finished four of them, it was leather hard. It usually takes them three days in the studio, so I was very happy. I trimmed and trimmed and it got thinner and thinner, but I didn’t punch a hole, or dent it too much, or any of the other possible trimming mishaps. In the end I was happy with the shape and as I lifted the batt I could feel it’s feather light. So I put it outside to dry more, exposing just the trimmed area, and went back to working on the teapots.
And when I finished them and went back out to check on the bowl, it was gone.
I’ve had stuff stolen from me before, usually involving bikes. I still remember staring at my bike in disbelief as I came out of the library to find my bike seat gone. But. A bowl. A beautiful, feather light, 14.5″ bowl (I had already run the shrinkage numbers in my head and was prepared for it to be 12.5 – 13″ when it’s fired. Well, don’t count your chickens before they’re hatched). A beautiful, feather light, 14.5″, UNFIRED bowl.
Porcelain is not known for its green strength. When it’s fired, it’s the strongest of clays. but green? look at it wrong and it will break.
So after the initial shock, I started laughing at the fool who stole my bowl-to-be. 7bs of clay, 20-30 minutes to throw and about the same time to trim. Some hopes, dreams about fired size and glazes. Thinking about it crumbling as he or she tries to use it.
I’ll make a better one next week.
(Hark! he speaks!)
An oil spot, naturally. Those glazes are somewhat of an obsession for me and the reason I fire my electric kiln to cone 9-9.75 and not to cone 6 like more sane people.
Here’s something I made in France:
It’s black, the gold is just the sun reflecting off the spots. Still pretty decent… and my first one. Little did I know how lucky I was to get this. This is what I thought was a common oil spot recipe called Candace Black. Of course I had to translate it to available materials, and some things got mangled in translation.
Here’s something I fired just a week ago, from a batch of bona fide North American material Candace Black:
The spots are numerous and delicate – quite different from the big distinct spots I got in France.
Aha, says the knowledgeable potter. The spots become bigger if you apply the glaze thicker. And they do:
Up to a point. Beyond which, disaster strikes:
The spots grow until they have nowhere else to go and then they lose the black background and just coalesce to a continuous metallic surface. And worse, they start to form unhealed bubbles.
Skip two months of painstaking testing, re testing, and reformulation… I think I’m getting somewhere:
And taking another line of research, also this:
Of course, these are small bowls that I made for testing glazes on… A different story from my 1.5 foot bowls that I’ve been dreading to glaze with a glaze that I’m not 100% sure about. We’ll see how it goes.
And while on the subject of bowls. Look what I’ve made!
Big, celadon, spiral(!)
I usually make my bowls ‘perfect’. This has caused me some aggravation since I believe the first duty of a functional pot is to function. A bowl needs to be smooth on the inside – so that if you use a spoon on it, it won’t grate. But I’ve been trying to push my boundaries. Leave the bottom smooth and push the ripple through the sides.
The spots were a surprise. Usually you get them if you don’t sieve the celadon well enough. I, however, put them there on purpose by wedging granular iron into my pristine porcelain… Not sure I’ll repeat the experiment although people inform me that it looks just like a robin’s egg.
There is actually a whole set of them – I made them to nest. But my bowls seem not to be team players – they are pots in their own right – really hard to get a multiple pot object to look good both individually and assembled. I’ll file the nesting bowl project under ‘needs more work’ and go back to admiring my celadon spiral.