Ceramics

Joss Research: Ceramics: Glazes: Rutile Blue

Joss Research Institute: Ceramics: Glazes: Rutile Blue

Recent Results
mid-December, 2004; February, 2005

December:

(2004 December 15, outdoor photos taken on the 16th)

These two objects, a vase and a bowl, have exactly the same glaze on (and in) them. The exteriors were sprayed in quick succession after I poured the interiors, and they were fired in the same kiln at the same time, right next to each other on the shelf. The main difference is the body: the vase is Loafer’s Glory, and the bowl is Helios. (Both bodies are made by Highwater Clays.) The firing went only to cone 9, because I couldn’t see the blasted cones for some reason, and I fired to temperature, which was (of course) inadequate.

                   

         

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

For those who care: I start reduction around 650 or 700 celsius, and continue until about 1220 (approximately cone 6, basically the point at which the glaze has skinned over and further reduction doesn’t accomplish much). For Copper Reds, I reduce only very lightly; but Rutile Blues seem to want a more aggressive reduction, so I bring the automotive oxygen sensor up to at

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Joss Research: Photographing Fluorescences

An Approach to Photographing Fluorescent Specimens with a Digital Camera

If you want to skip the technical details, click here to jump to the photo section.

Issues

While digital cameras are not overly sensitive to UV, they can certainly pick up some of it, and the results make it difficult to photograph fluorescent specimens with them. When I tried to take a photograph of the green fluorescence of a Calcium Tungstate crystal glaze that I had activated with Erbium Oxide, instead of getting a green spot where the UV from my ultraviolet LED was hitting the tile, I got a bright pink spot.

I was not surprised to find that the blue pixels in my camera were picking up a little of the near-UV, but it came as something of a shock to discover that the red pixels were sensitive around 355 or 360 nm: when I took the same photo through a prism, following a suggestion made by Nancy Lebovitz, I got a green spot, and also blue and red spots that overlapped —

(Notice that the red is actually on the short-wavelength side of the blue. My guess is that either the red filters in the sensor

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Joss Research: Ceramics: Glazes: Red Temmoku

“Red Temmoku”

(11 October, 2004, with a followup)

Here is a Red Temmoku bowl, fired to cone 10r. The bowl is about
6 across. It is made of Loafer’s Glory, from
Highwater Clays;
the glaze consists of Brick Clay from western Wisconsin;
Wood Ash (Oak, unwashed); and Red Iron Oxide (84% purity).
I strongly suspect that the yellow teadusty or
“corn-pollen” sprinkles, which show up
particularly well on the interior, result from the ~2.6%
MgO content of the Brick Clay; I get essentially the
same effect in other iron-rich glazes if I add enough
Mg. (Oddly, although all or nearly all of the ancient
Chinese high-iron Jianware glazes contain noticeable
MgO, very few modern Western “Temmoku”
glazes seem to use magnesium. Go figure.)

(Click any of the small photos to get one that is
1280×960 px. If you want something even larger, you can
change the “.10c.” in the filename of the
large image to “.22c.” for the full-size
originals, 2272×1704; just be aware that those files are
about 1.5 MB each, and may take a while to download if
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SnowCaT / Extending the Color Range

Extending the Range: Novel Rare-Earth Colorants

(08 April, 2005)

In the process of developing a glaze that precipitates crystals of calcium tungstate (CaWO4, Scheelite), I happened to dip the edge of a test tile into a solution of europium nitrate. Where the glaze and the dipped area overlapped, the glaze was brownish after I fired the tile.

Some time later, while I was refining the glaze, I decided to try Eu2O3 as a colorant, to see whether it would be of any interest. I started with 1%, and then added 6% of Er2O3 on top of that, to see what the combination would look like. The tiles were fired to cone 11 in mild reduction:


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This seemed quite promising, but the glaze was thin and watery, rather than thick and cloudy, so I continued to revise it. The next firing was v0.4, this time to about cone 10.5, in moderate reduction; from left to right, plain, with 2.5% Eu2O3, and Eu plus 6% Er2O3:


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It seemed like a good idea to try this with Mo in place of W, so I did, approximately an equimolar amount. Again, from the left: plain, 2.5% Eu, Eu + 6% Er:

As

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