Ceramics

Joss Research: Ceramics: Glazes: Copper Red

Ancient Nanotechnology:

(2004 March 13)

The Chinese have been making wonderful red glazes with copper in them since at least the mid-1400s. There have been various versions at different times, and the history is quite interesting. (There is a fine chapter on copper colorants in Chinese Glazes, by Nigel Wood.) It turns out that the red color is an early example of nanotechnology: it is caused by a colloidal suspension of copper nanocrystals, some tens of nanometers on a side. (I think they range from ~20 to ~200 nm across, but don’t quote me.) Richard Zsigmondy got a Nobel prize in 1925 for achieving a systematic understanding of colloids; he invented the ultramicroscope in the process of his research.

Copper Red glazes are notoriously difficult and fickle. It’s debatable whether this is inherent, but there’s no question that it’s The Usual State of Affairs. I started trying to make a decent, noncrazing Copper Red in 1996 or 1997, and have made Copper Gray, Copper Grayish-Pink, a color that is probably the one the ancient Chinese called “Mule’s Liver”, and various other wretched failures. I’ve even made one that wasn’t too bad — it came out a rich purplish red. (Darker

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Joss Research: Fluorescent Glaze Photographs for Clay Times Magazine

Joss Research: Ceramics: Fluorescent Glazes

Photographs for Clay Times Magazine

(05 April, 2005)

NOTE: If you click any of the small images, you get the original 2272×1704 pixels. The large images are JPEGs at the highest quality setting my camera provides. If you prefer TIFFs, I can either convert for you, or set my camera appropriately and reshoot, though I doubt that you’ll see any difference. (We can certainly test that conjecture if you’d like.)

Ginny Conrow Bowl

This bowl is about 4″ across. It was made by Ginny Conrow, in Seattle, and is covered with a zinc-silicate crystal glaze that contains a small amount of Mn, probably between 0.5% and 1%. From the left: daylight, longwave (“blacklight”) UV, shortwave UV.

               

Here’s an alternative blacklight pic of this bowl that I actually like better than the middle one above:


Fluorescent Porcelain Bowl

This bowl is about 3″ across. It is my porcelain, with Europium in it, fired in reduction. The first photo was taken in roomlight, the second in combined roomlight and blacklight.

       


Test Tiles

Here are some fluorescent test tiles. With one exception (Ruby Dust in a clear glaze, lower left corner of the array), they all involve rare

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Joss Research: Ceramics: Glazes: Glaze Tests and a Bowl, Spring 2004

A Joss Research Interim Report: Ceramics

Firing Results: 28 April, 5 May, and 27 May, 2004

(May, 2004)

I have recently fired several glaze tests, some of which returned results that I consider interesting enough to report, and a pot or two. Here are some pictures and explanations.

  • I’ve been working on replicating the ancient Chinese “Tortoiseshell Tenmoku” glaze for a while; these tests provided the best results I’ve gotten so far:

         

    I took the firing to cone 9, but with a fairly long soak that started when cone 8 just began to move, with the temperature held almost constant until cone 9 slumped. Cone 9 is a bit on the hot side for tortoiseshell, so the base glaze is darker and both the base and the spots are more transparent than they would probably be if I’d fired them lower. (Just for reference: under common conditions, cone 8 roughly approximates to 1240° celsius, and cone 9 to 1260°. They don’t really measure temperature, though, and in this case I was probably holding the kiln at 1225 or so for two and a half hours.)

  • Another ancient Chinese glaze I’ve been working on copying is the black that was used

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Joss Research: Ceramics: Glazes: “Black Satin”

Another Serendipitous Excitement: “Black Satin” Glaze

(2007 December 03)

Some time ago I developed a coffee-and-milk brown glaze with a semigloss surface, which you can see in the first two photos. (Teacup, collection of Dr. Harris Iskandar.) It is based on Redart Clay, to which I had to add quite a bit of flux to get it to melt. The glaze is fired to cone 9, in air, in an electric kiln.

         

(As usual, click any of the small images to get a larger version.)

I wanted a more silky/satiny surface, and was still tweaking and testing the glaze, when Something Peculiar happened during a firing. The next photo shows what the transformed glaze looks like. (Bowl, collection of Dr. Alfred and Isabel Bader.)

The overall color is a dark charcoal gray, and there is a dancing play of colors across it that is best seen in bright light. Where it thins out on edges and ridges it is dark red-brown.

It took me a while to figure out exactly what had caused the effect; I hope to get an article out of this, so I would prefer not to get into specifics just yet, but I can say that

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Glaze Tests, Autumn of 2004

Firing Results, starting 29 September, 2004

A Joss Research Institute Interim Report

(30 September, 2004)

I fired two glaze tests yesterday, one of which provided an odd and interesting result.

In the Spring, I reported on a found material, some apparent low-grade iron ore that occurs in the “panhandle” section of Maryland, and in southern Pennsylvania and New York. A few weeks ago, I managed to collect a sample from each of those two states. Here’s the Pennsylvania material, sitting out in front of #19:

     

I melted a material very similar to this (actually a Maryland sample) at cone 9 or so in the electric kiln, this past spring, and got the following:

     

In addition to the Maryland and Pennsylvania samples I got a sample of the equivalent rock from upstate New York, already weathered and crumbled. I ran some of it through the jar mill, and it fired out much like the example shown above, but perhaps a slightly richer color, so I’ve begun mixing it with fluxes to see what kinds of glazes I can get from it. Yesterday’s mix was 90% “NY State Red Rock”, 4% Whiting, 4% Magnesium Carbonate, and 2% Red Iron Oxide (84% purity).

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Along The Red Temmoku Trail

Red Temmoku, the Story of an Obsession

(14 January and 04-06 March, 2001, with later continuations)

Soon after I got involved in pottery I discovered that there were glazes I wanted to use on my pieces, but didn’t find among the ones I had access to. I also discovered that I didn’t really like most of the ones that were available to me. No surprise, I soon found myself trying to mix a few of my own. This page is the story of one of them, a Temmoku variant that I hoped would be a deep rich transparent cherry-mahogany red in bright light, rather than the apparent black of most Temmoku glazes.


Sidebar: Tenmoku vs Temmoku

The term “Tenmoku”, regrettably often spelled “Temmoku” these days, appears to be the Japanese version of Tian mu Shan, “Heaven’s Eye Mountain”, an area in China where tea is grown and teaware was (and perhaps still is) used by monks, but not apparently made. The major styles of teaware that are referred to by the term “Tenmoku” were manufactured in the Jian and Jizhou regions, and transported to many places in China.

Teabowls were brought to Japan, apparently by monks who had visited

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Ceramics at the Joss Research Institute

Ceramics at The Joss Research Institute

Some publications:

  • Rutile Blue
    Studio Potter, Volume 35 Number 1, December, 2006;
    I regret that the photo in the article fails to do justice to the bowl in question. (Largely my fault.) Here is a slightly better one.
  • Fluorescent Glazes
    Clay Times, May/June 2005, pp48-52;
    You can find photos (including some items that were not in the article, as well as some technical information) by following the link I give below.
  • Recreating the Black Ding Glaze
    Studio Potter, Volume 33 Number 1, December, 2004;
    (Again, see below for a link to online versions of the photos, as well as some ancillary information.)
  • I hope to have one or more articles out fairly soon about other work I’ve been doing, some of it with translucent porcelain.


Pages about my work:

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Joss Research: Kilns: Gas Firing: A Larger Burner

Joss Research: A Second Forced-Air Burner

(2003 November 3)

Having [after some travail] gotten good results with my previous forced-air burner, I decided to build a larger one. I’m using a very nice EG&G Rotron fan that came out of a disused microwave transmitter; it pulls almost 3 amps, so I think the motor (which is remarkably compact) is putting out 1/3 hp. It’s a cute design, too — the inlet air helps cool the motor.

The design is quite similar to the earlier one, but I used 2″ pipe for the outer jacket on this one, and 2″ fittings. When I first tested it, the flame kept blowing off. The blower design, as you can see from the photos, doesn’t really let me block off its air inlet, so instead I added a second pipe tee and a damper to bleed off some of the air coming out of the blower, in a more or less controlled manner. I lucked out with the parts for the spill — the 4″-to-3″ galvanized sheet-metal adapter from the hardware store just fits over the pipe tee, and is held on by a hose clamp. I probably would have preferred a slightly more

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Joss Research: Ceramics: Glazes: “Rumoku”

Adding Rutile to High-Iron Glazes

(2005 March 15)

This little covered jar was fired to cone 9 in reduction. It is about 4.5 or 5″ across, and not quite as tall as it is wide. The glaze contains 6.5% RIO and 4% Ceramic Rutile. The effect is vaguely similar to “hare’s fur”, but has its own character, which I rather like. It works moderately well in oxidation, but wants a soak to let the pinholes even out. In reduction, however, it is generally well behaved, as you can see. (I should point out that I sprayed the glaze onto this piece, in order to get a reasonably even coating thickness.)

         

(As usual, click either of the small images to get a larger version.)

For those who care: I ordinarily start mild reduction around 750° Celsius, and continue until approximately cone 6, basically the point at which the glaze has skinned over and further reduction becomes largely pointless (about 1220° C). I then reduce the gas flow until the flame is more or less neutral, and I keep it that way until the end of the firing, which is ordinarily at cone 10. (My test kiln is very small, and it

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