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 2272x1704 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 earths. With that and one other exception (“ErbCaT”, at the right edge of the middle row) they are all in my regular “M9” clear glaze. (I don’t know what glaze the Ruby is in — it’s several years old. My apologies.)

The Ruby (red), Samarium (orange) and Europium (magenta-pink) tiles in the bottom row were fired in oxidation; the rest were fired in reduction, as that tends to produce slightly brighter, clearer colors. (In the case of Cerium, it seems to be necessary; Cerium fusses and bubbles when I fire it in oxidation.) The concentration of the colorant is 3%, as oxide, except where I’ve indicated otherwise in the descriptions below.


Here are photos of the tiles, in smaller groups.

First row: array of tiles, in roomlight and then under “blacklight” longwave UV illumination, provided by a UV Products B100A lamp. Notice that the tiles in the top row are very much brighter than all the others. This is a good indication of relative brightness: Europium (II) outshines all other fluorescent materials that I’ve tested so far. (I should note that I have not tested Uranium, which is known to have a particularly bright fluorescence.) I will try to reshoot the blacklight version of this, as the camera apparently moved during the exposure, blurring the image.

Second row: 6% Ruby Dust in a clear glaze and Europium fired in oxidation; then Samarium fired in oxidation and Dysprosium. My apologies for the fluorescent speckles on the Ruby tile — I washed it twice, and that was about as clean as I could get it, despite considerable scrubbing with a toothbrush.

Third row: Terbium in M9 Clear, and a Calcium Tungstate glaze (“Fa & Jon’s SnowCaT”) to which I’ve added 4% Erbium Oxide to make the “Pink Snow” version. Again, my apologies for the schmutz on that tile.

Fourth row: 1% Europium and 3% Europium, both fired in reduction; then 1% Europium and 3% Cerium, both fired in reduction.

Fifth row: Samarium, Terbium, and Cerium. The Sm was fired in oxidation.



Note that 1% Europium (lefthand tile in both photos in the fourth row) is brighter than either 3% Europium or 3% Cerium. Note also that Cerium is a deeper blue than Europium, in this particular glaze. (The color of the fluorescence of Eu (II) is highly variable, and depends strongly on the environment that surrounds the Europium ion. In my glazes it is usually a sky-blue color, as you see here.)


Here is a head-to-head comparison of the “M9” clear glaze (3% Terbium added) with a zinc-silicate crystal glaze containing Mn. Notice that in one spot where the crystal glaze did not make a crystal, there is no fluorescence.

Here are two daylight photos. The first shows M9 Clear with 1% Europium Oxide added, and M9 Clear with 3% Europium Oxide added. Note the faint greenish tinge, much more easily visible in the tile on the right.

The second photo shows the clear glaze with Ruby dust in it, and the “Pink Snow” glaze.


Sorry about the failed background. I was in a rush when I took these.

This work was supported by
The Joss Research Institute

Contact Information:

Email:, where you can replace a with my first name (jon, only 3 letters, no “h”) and b with joss.

Phone: +1 240 604 4495.

Last modified: Wed May 10 11:43:33 EDT 2017