Joss Research Institute: Ceramics: Glazes: Rutile Blue

Recent Results
mid-December, 2004; February, 2005


(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 least 650 or 700 millivolts. When the kiln reaches 1220° c, I reduce the gas flow until the flame is more or less neutral to slightly oxidizing, and I keep it that way until the end of the firing.

Note: If you have a fast connection to the net and you want more detail, here are the original pixels.

Vase, overall view.
Vase, detail of top.
Vase, detail of side.
Outside of the bowl.
Inside of the bowl.


(February 2, 2005)

I have, at least for the moment, settled on a formulation that is intermediate between the "no added iron or copper" and "0.5% RIO, 0.3% RCO" extremes. Because it has some Fe and Cu in it, this version of the glaze makes reasonably rich colors on porcelain. Here’s a Helios teabowl I fired to cone 9 in moderate reduction on February 1st:


As before, the interior is poured and the exterior is sprayed. I like spraying, at least for the outside, as it gives me a bit more control and lets me get some effects that are not easily created by dipping.

As usual, you can click any of the small images to get a larger one (800 x 600 px). If you are a real glutton for punishment, you can view any of the 800x600 images above and change the filename so that "8c" becomes "22c". That gets you the original 2272 x 1704 px image. Alternatively, just click any of the small images below for a rather large detail closeup. (These are all in excess of 1400 px across.)


(This bowl is in the collection of Lisa Peoples, and the photos are shown here by permission.)

Here is the same glaze on Loafer’s Glory, from the same firing. You’ll notice that the colors are deeper and tend, perhaps, a bit more toward the red. Again, if you want large images, click any of the small ones. If you want the full originals, change "8c" to "22c" in the filename of the 800x600 image.


(This bowl is in the collection of Fa and Bob Shimbo, and the photos are shown here by permission.)


(15 February, 2005)

I glazed and fired these two bowls today, taking them to cone 10 in moderate reduction. They illustrate some of the reasons why I spray my rutile blue glaze...



...and also some of the problems with Rutile Blues (note the pinholes in the glaze) and the variability or unpredictability involved in spraying. While I like the gold color just below the rim in the first bowl, it was not quite what I had in mind. Also, please note the huge differences in color between the two bowls. These bowls are made of the same material, Helios porcelain (the "H" on the bottom); they were glazed within minutes of each other, from the same jar of glaze (in fact, the same jar that glazed the two bowls from the beginning of February); and they were fired together. The color differences seem to be entirely an issue of glaze thickness, while the visual texture of the lower bowl, as if the glaze had fallen in little clouds or snowflakes, is an artifact of the amount of water in the glaze slip and the characteristics of the sprayer, as far as I can tell.

If you want more pixels, you can change ".8c." to ".22c." in the regular shots. In the side views and interior details, in the upper set, 205rc1 goes to 15c and 222c1 goes to 13c; in the lower set, 204c1 and 221c1 go to 16c, and 223c1 goes to 14c — they’re crops from the original images.

Onward to Modest Reproducibility

(24 February, 2005)

I glazed and fired two bowls a couple days ago, to cone 10. both of them showed a certain amount of blond or gold just below the rim, and it’s clear that the "gold ring" is not just the gold at the end of the rainbow. Both are mid-blue, with less color variation than the bowl just above, and little or no purple, but they are quite pleasant nonetheless. I did a bowl and a vase today, taking them to cone 9 in moderate reduction. Here’s a quick view of the bowl:

The lightly glazed area below the rim on the interior is not golden, but it’s reasonably pleasant. The interior has somewhat richer color than either of the two bowls I fired the other day. I’m clearly learning how to exert at least modest control over this, which is a happy thing. Note that this photo was taken in mediocre roomlight, and that proper lighting might reveal a bit more color.

This work is supported by
The Joss Research Institute
19 Main St.
Laurel  MD  20707-4303   USA

Contact Information:

email:, where a is replaced by my first name (just jon, only 3 letters, no “h”, and b is replaced by joss.

My phone number is +1 240 604 4495.

Last modified: Tue May 9 11:35:37 EDT 2017