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
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 you are on a slow connection.)
This bowl
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
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
