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Rutile

Iron Titanium Mineral

Formula: TiO2

OxideAnalysisFormula
TiO290.00%1.000
Fe2O310.00%0.055
LOI0.10
Oxide Weight88.78
Formula Weight88.87
If this formula is not unified correctly please contact us.
DENS - Density (Specific Gravity) 4.20
HMOH - Hardness (Moh) 6.0-6.5
GSPT - Frit Softening Point 1600C M

Rutile is the mineral name for natural crystals of titanium dioxide. In nature rutile is always contaminated by up to 15% other minerals (especially iron but also things like tantalum, niobium, chromium and tin). The term 'rutile' is thus generally understood to refer to the brown powder into which these minerals are ground and industry accepts up to 15% contaminants and yet still calls it rutile (below 85% titanium is called ilmenite). Rutile is considered an impure form of titanium whereas ilmenite is considered as FeTiO3. Grades of rutile are sometimes named after one of the impurities (e.g. Niobian Rutile). Rutile is used in many industries (e.g. welding rods, paint) and ceramic uses are minor in comparison (for this reason bags of rutile might have labels like "Welding Rod Titanate"). Rutile is often sourced by companies in the titania and zircon supply business. The are large reserves of rutile in the world and any supply shortages are thus related to other factors.

Rutile is available in light calcined ceramic grade powder (very fine particle size), dark uncalcined powder, and granular form. Either grade of powder can be ground very fine (e.g. 325 mesh). In glazes it is generally better to use the ceramic grade since the decomposition of raw rutile during firing can be a source of glaze imperfections like pinholing and bubbles (even larger amounts of the ceramic grade, e.g. 8%, can also cause problems).

Rutile produces many crystalline, speckling, streaking, and mottling effects in glazes during cooling in the kiln and has been used in all types of colored glazes to enhance the surface character. It is thus highly prized by potters, many attractive variegated glazes are made using it. Many potters would say that their living depends on their rutile supply!

This material can be inconsistent in the amount of iron and impurities producing variations in color and surface character, thus manufacturers will blend ores from different deposits (Ferro in the US blends various Australian materials in addition to material from Florida). For example, one major American supplier, TAM (now Ferro), relied on a high quality Sierra Leonian rutile deposit until 1995 when political problems in the country cut the supply. Since then no other substitute has provided the same quality. Considering that it is the metallic coloring impurities in rutile that are the subject of its variation and that the function of rutile in glazes is most often partly or mainly as a colorant, it is easy to see that visual consistency variations can be expected when using this material in ceramic glazes. Large users of rutile will often track batch numbers from the manufacturer and test when the number changes. If serious differences are detected another batch may be requested. Failing this the situation can sometimes be dealt with by adjusting the amount of rutile in the recipe or firing differently. In more serious situations adjusting the recipe and employing other materials like iron and titanium might be needed. In any case, it is important to understand the base glaze and the mechanisms by which rutile imparts the desired visual effect. Buying large amounts of a batch that works well is thus a good idea with a material like rutile.

Rutile is very refractory in oxidation, even a mix of 50% borax alumina-free frit like Ferro 3134 will not melt rutile in a crucible. In reduction, the improvement in melting will depend on the amount of iron present.

In ceramic glazes rutile is more often considered a variegator than a colorant. As little as 2% can impart significant effects in stoneware glazes. It is normally used in combination with a wide range of metal oxide and stain colorants to produce surfaces that are much more visually interesting. In glazes with high melt fluidity (e.g. having high boron), large amounts of rutile (e.g. 6-8%) can be quite stunning. The rutile encourages the development of micro-crystals (it is crystalline itself) and rivulets. Since rutile contains significant iron its use in combination with other colorants will often muddy the color that they would otherwise have or alter it if they are sensitive to the presence of iron. Even though rutile generally makes up less than 5% of stoneware glazes that employ it, they are often called 'rutile glazes' in recognition of its dramatic contribution.

Excessive rutile in a glaze can produce surface imperfections. In addition, when rutile is employed in higher percentages (e.g. 5%+) a given percentage might work well whereas a slightly higher amount can look drastically different. Such situations are vulnerable to chemistry changes in the supply of rutile. Thus people will often do a line blend trying a range of percentages to determine an optimal amount.

In glazes rutile can be quite sensitive to the presence of opacifiers. While an unopacified glaze glaze might appear quite stunning, the addition of a zircon opacifier will usually drastically alter its appearance and interest because the variegation imparted is dependent on the glaze having depth and transparency or translucency. Strangely rutile and tin, another opacifier, can produce some very interesting reactions and it is quite common to see tin in amounts of up to 4% in rutile glazes. In these cases the tin appears to react in the crystal formation rather than opacify the glaze.

Rutile powder, although its color makes it appear to be a very crude ground mineral, normally contains 90%+ titanium dioxide. However this does not mean that you can use a 90% titanium:10% iron mix and get the same result in a ceramic glaze (obviously line blending would be needed to match the amount of iron). The mineralogy and significant other impurities in rutile are a major factor in the way it acts in glazes and are not easily duplicated using a blend of other things. Sometimes the special effects that rutile produces in glazes are also partly a product of a coarser grade (larger particle size). These likewise cannot be easily duplicated by more refined materials. Unfortunately the trend at some mining operations (at least in Australia) is to fine grind the rutile on-site, making it more difficult for ceramic operations to obtain the coarser grades.

Although rutile will normally stain a glaze brown or yellow, its crystallization effects can significantly lighten the color of iron glazes. Higher amounts of rutile in stoneware glazes will often contribute glaze imperfections.

Granular rutile is sometimes used in bodies and glazes to impart fired speckle.

Rutile is used for special effects in leaded glazes and can form up to 15% of the recipe.

Rutile can be used as a tone modifier to soften the more potent colorants.

Richard Willis

Mineral,TiO2,with a typical empirical analysis of Ti 59.95%, O2 40.05%
Hardness: 6-6.5 Density: 4.2-4.3 Insoluble in acids
The metal crystals commonly coating welding rods. In pottery TiO2 is one of the most common ways of introducing titanium to a recipe. Strong refractory and opacifier. see brookite, ilmenite, sagenite

Mechanisms

A fluid reduction rutile glaze is crawling

A fluid reduction rutile glaze is crawling

Crystallization of Rutile at cone 6 completely subdued? How?

Crystallization of Rutile at cone 6 completely subdued? How?

These glazes are both 80% Alberta Slip, but the one on the right employs 20% Ferro Frit 3249 accelerate the melting (whereas the left one has 20% Frit 3134). Even though Frit 3249 is higher in boron and should melt better, its high MgO stiffens the glaze melt denying the mobility needed for the crystal growth.

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

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 1400C. 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?

Reduction high temperature iron crystal glaze

Reduction high temperature iron crystal glaze

This is what about 10% iron and some titanium and rutile can do in a transparent base glaze with slow cooling at cone 10R on a refined porcelain.

The rutile mechanism in glazes

The rutile mechanism in glazes

2,3,4,5% rutile added to a 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.

The rutile mechanism in glazes

Rutilite Slices

The rutile mechanism in glazes

Rutile Crystals

The rutile mechanism in glazes

Rutilated Quartz2

The rutile mechanism in glazes

Rutilated Quartz

The rutile mechanism in glazes

Quartz Rutilated

The rutile mechanism in glazes

Phonolite Rutile

Tin oxide can stop the rutile variegation effect dead in its tracks!

Tin oxide can stop the rutile variegation effect dead in its tracks!

This is Alberta Slip (GA6C) on the left. Added frit is melting the Alberta Slip clay to it flows well at cone 6 and added rutile is creating the blue variegated effect (in the absence of expensive cobalt). However GA6D (right) is the same glaze with added Tin Oxide. The tin completely immobilizes the rutile blue effect, it brings out the color of the iron (from the rutile and the body).

How do metal oxides compare in their degrees of melting?

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.

Variegation and phase separation with about 5% rutile

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.

MgO can destroy the rutile blue variegation effect

MgO can destroy the rutile blue variegation effect

The rutile blue variegation effect is fragile. It needs the right melt fluidity, the right chemistry and the right cooling (during firing). This is Alberta Slip GA6C recipe on the right (normal), the glaze melt flows well due to a 20% addition of Ferro Frit 3134 (a very low melting glass). On the left Boraq has been used as the flux (it is a calcium borate and also melts low, but not as low as the frit). It also contains significant MgO. These two factors have destroyed the rutile blue effect!

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

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.

Variegating effect of sprayed-on layer of 100% titanium dioxide

Variegating effect of sprayed-on layer of 100% titanium dioxide

The referred to surface is the outside of this large bowl. The base glaze (inside and out) is GA6-D Alberta Slip glaze fired at cone 6 on a buff stoneware. The thinness of the rutile needs to be controlled carefully, the only practical method to apply it is by spraying. The dramatical effect is a real testament to the variegating power of TiO2. An advantage of this technique is the source: Titanium dioxide instead of sourcing TiO2 from the often troublesome rutile.

Blisters in a reduction fired rutile glaze

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.

Alberta Slip Rutile-blue needs Frit 3134, it does not work with others

Alberta Slip Rutile-blue needs Frit 3134, it does not work with others

These two cone 6 mugs have the same glaze recipe: GA6A Alberta Slip base. 4% rutile has been added to each. They were fired in the same kiln using a slow cool schedule. The recipes and chemistry are shown below (the latter gives a clue as to why there is no blue on the right). The mug on the left is the traditional recipe, 80:20 Alberta Slip:Ferro Frit 3134. Frit 3134 melts at a very low temperature and a key reason for that is its near-zero Al2O3 content. Al2O3 in glazes stiffens the melt and imparts durability to the fired glass (normally we want adequate levels in functional glazes). When Al2O3 levels are low and cooling is slower molecules in the stiffening glass have much more freedom to move and orient themselves in the preferred way: crystalline (fast cooling produces a glass). Thus the rutile in the glaze on the left has had its way, dancing as the kiln cooled, producing all sorts of interesting variegated visual effects. The glaze on the right employs Ferro Frit 3195. It has lots of Al2O3 and has contributed enough to stop the rutile dead.

Out Bound Links

In Bound Links


By Tony Hansen

XML for Import into INSIGHT

<?xml version="1.0" encoding="UTF-8"?> <material name="Rutile" descrip="Iron Titanium Mineral" searchkey="" loi="0.00" casnumber="98084-96-9"> <oxides> <oxide symbol="TiO2" name="Titanium Dioxide, Titania" status="" percent="90.000" tolerance=""/> <oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="10.000" tolerance=""/> </oxides> <volatiles> <volatile symbol="LOI" name="Loss on Ignition" percent="0.100" tolerance=""/> </volatiles> </material>


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