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Ceramic Rutile

Alternate Names: Calcined Rutile, Light Rutile, Rutile Ceramic

Oxide Analysis Formula
TiO2 96.09% 245.34
ZrO 1.20% 2.28
Al2O3 0.50% 1.00
SiO2 0.80% 2.72
Cr2O3 0.20% 0.27
Fe2O3 0.50% 0.64
V2O5 0.70% 0.79
Oxide Weight 20,397.96
Formula Weight 20,397.96

Notes

This is a much lighter color than raw granular rutile (because it is ground to minus 325 mesh and calcined). It is the recommended type for use in ceramic glazes since it will not produce gases of decomposition. See Rutile topic for much more information.

The theoretical chemistry is TiO2, but of course no mineral deposit has this. We have shown the chemistry of a commercial material whose original container bags are labelled "Weld Rod Titanate" (used in making welding rods). However, the percentage of iron looks suspiciously low considering how dark the color is when fired.

Related Information

Variegation and phase separation with about 5% rutile

The glaze is a dolomite matte fired to cone 10R. High fire reduction is among the best processes to exploit the variegating magic of rutile.

6% rutile is too much in this cone 6 oxidation glaze

Rutile variegates glaze surfaces. But it also opacifies at higher percentages. The blue effect is a product of crystallization that occurs during cooling, it is thus dependent on a slower cooling cycle, especially above 1400F. This is GA6-C Alberta Slip glaze with 4, 5 and 6% rutile. At 6% the rutile crystallization has advanced to the point of completely opacifying the glaze. At 5% the blue is still strong, even on a buff burning body. The loss of color occurs suddenly, somewhere between 5 and 6 percent. Rutile chemistry varies from batch to batch. The blue develops differently on different bodies. So do you want to play "at the edge", with 5% in the glaze, in view of these other factors and the finicky firing curve needed. Change in any of which could push it into the blueless zone?

How much rutile can a glaze take before it becomes unstable?

The 80:20 base Alberta slip base becomes oatmeal when over saturated with rutile or titanium (left:6% rutile, 3% titanium; right:4% rutile, 2% titanium right). That oatmeal effect is actually the excess titanium crystallizing out of solution in the melt as the kiln cools. Although the visual effects can be interesting, the micro-crystalline surface is often susceptible to cutlery marking and leaching. This is because the crystals are not as stable or durable as the glass of the glaze.

An original container bag of ceramic rutile

The primary use of this material is obvious. It is not ceramics. But this bag is marked at "ceramic grade", likely a reference to its fine particle size. This bag is very small, ceramic rutile is very dense.

Blisters in a reduction fired rutile glaze

This is a common problem with these glazes. The visual effect is very compelling but also punishing! Potters experiment with higher bisque firing and soaking during bisque. They try cleaner clay bodies. They employ long hold periods at temperature in the glaze firing. But the problem persists. The solution is actually simpler. These glazes have a high melt fluidity and enough surface tension to hold a bubble static during soaks at temperature (no matter how long you hold it). It is better to cool the kiln somewhat (perhaps 100F) and soak at that temperature. Why? Because the increasing viscosity of the melt overcomes the surface tension that maintains the bubbles. You may need to cool more or less than 100 degrees, but start with that.

Two G2571A Bamboo color versions at cone 10R

These mugs are Plainsman H450. Both have a black engobe (L3954N) applied to the insides and half way down the outside during leather hard stage (the insides are glazed with Ravenscrag silky matte and G1947U over the black engobe). The bamboo glazes can thus be seen over the black (upper half) and the raw buff body (lower). The bamboo glaze on the left has 1% iron added to the base G2571A recipe. The one on the right has 3.5% powdered rutile and 10% zircopax added.

Cone 6 rutile blue glaze on a black porcelain body

Glaze is GA6-C Alberta Slip rutile blue. Fired at cone 6. "Mother Nature's porcelain" has 6% Mason 6600 black stain.

Possible to grind your own ceramic grade rutile?

Yes, the granular and powdered grades are the same material. But grinding it is very difficult. Commercial ceramic grade powder is minus 325 mesh, the companies doing this obviously have very good grinding equipment. They also have patience because even in this efficient porcelain ball mill, 90 minutes was only enough to get 50% to minus 325 mesh! The color of the powder is a good indication of its quality, the finer the grind the lighter will be the tan coloration.

Making your own ceramic rutile

Left: GA6-C rutile blue glaze on a brown stoneware. The 4% ceramic rutile powder gives the blue variegated effect. Right: We ball-milled our granular rutile and then screened it down to 325 mesh and put that into the same glaze. The results are the same. So if any of your rutile glazes ever lose this effect with a new supply of the material the cause could be that it has not been milled sufficiently fine. Finer rutile powders are browner in color.

4% rutile in a low temperature transparent glaze

The glaze is G191T (a variation of G1916Q). Firing was cone 04 drop-and-hold with slow cool. Sometimes a raw colorant is advisable over a ceramic stain. At low temperatures stains are almost universal. But in this case, the orangey-yellow color that rutile produces merits further testing. On the red body (Plainsman L215) the color is barely perceptible, but on the light Buffstone body it is working well. The variations in thickness highlight contours better than what a stain would do.

The rutile mechanism in glazes

2, 3, 4, 5% rutile added to an 80:20 mix of Alberta Slip:Frit 3134 at cone 6. This variegating mechanism of rutile is well-known among potters. Rutile can be added to many glazes to variegate existing color and opacification. If more rutile is added the surface turns an ugly yellow in a mass of titanium crystals.

How do metal oxides compare in their degrees of melting?

Metallic oxides with 50% Ferro frit 3134 in crucibles at cone 6ox. Chrome and rutile have not melted, copper and cobalt are extremely active melters. Cobalt and copper have crystallized during cooling, manganese has formed an iridescent glass.

Rutile blue glazes: Love the look, hate the trouble to make it

A closeup of a cone 10R rutile blue (it is highlighted in the video: A Broken Glaze Meets Insight-Live and a Magic Material). Beautiful glazes like this, especially rutile blues, often have serious issues (like blistering, crazing), but they can be fixed.

Three rutile blue glazes at cone 6

Three mugs with floating blue glazes

These are GA6-C Alberta Slip floating blue, AMACO Potter's Choice PC-20 Blue Rutile, GR6-M Ravenscrag floating blue. The clay is M390. The firing is cone 6, the schedule is C6DHSC (drop-and-hold, slow cool). The inside is GA6-B. The two on the left develop the blue color because of the slow-cool, the one on the right works on fast-cool because it contains cobalt (although it will fire somewhat more mottled). The centre one is a bottled commercial product, it was painted on in three coats. The result is quite compelling, this is a good place to start if you want the rutile-blue effect. Remember, these work best on dark-burning bodies.

Links

Materials Rutile
Glossary Rutile Glaze
A type of ceramic glaze in which the surface variegates and crystallizes (on cooling) from the presence of rutile mineral in the recipe.
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Opacifier
Opacifiers are powders that turn transparent glazes opaque by various chemical and physical mechanisms (and combinations of mechanisms).
Typecodes Colorant
Metallic based materials that impart fired color to glazes and bodies.

By Tony Hansen


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