Edouard Bastarache on sun 29 nov 98
Hello Tom,
The percentage of titanium dioxide varies from one ilmenite mine to another
one.
There is a mine in Madagascar where it is close to 62%, probably where your
analysis comes from. Dupont owns one in Florida where it is close to 52%,
while QIT-Quebec Iron and Titanium's is in the vicinity of 30%; it is the
one
with the lowest percentage in the world and the mine is very very large.
Later
Edouard Bastarache
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
----------
> De : Tom Buck
> A : CLAYART@LSV.UKY.EDU
> Objet : unusual colours at C6 ox
> Date : 28 novembre, 1998 15:51
>
> ----------------------------Original message----------------------------
> Caryl W:
> Ron Roy noted your two glazes (Butterscotch, Seafoam Blue) are
> "balanced" for C6 which is good. I'd like add data on colour effects,
info
> I had prepared earlier and sent offline to another Clayarter.
> Why the different colours, and why do they change when the order
> of application is changed? Well, one cannot give you a precise
> explanation without chemically analyzing the fired glaze on a pot.
> However, the likely culprit is the level of Titanium oxide in the
> combo, espy at the surface.
> Parmelee/Harmon note in "Ceramic Glazes" that titanium oxide will
> yield a range of colours in many alumino-silicate melts. Here is a bit of
> what they and others say (I wrote this earlier, $ are Canadian):
>
> Veronica:
> I have prepared for you the following summary of titanium
> materials and their glaze effects.
>
> Titanium "raw" materials
> There are available commerically three varieties/forms of
> materials containing titanium dioxide:
> 1) Ilmenite, a natural crystalline mineral that combines
> titanium dioxide and iron oxide, reported as 62% TiO2 + 26% Fe2O3
> plus small amounts of alumina and silica. Although the composition
> (ultimate analysis) of ilmenite is reported as above, the crystal
> is actually repeating units of TiO2 and FeO. It is chemically
> very stable. Ilmenite is sold in two grades (particle sizes),
> namely granular and milled, and costs approx. $4/kilo in small
> amounts, $1.60 when a 44 kg bag is purchased. It is a black
> powder, granular staying on an 80-mesh screen, milled grade
> goes through this screen.
> 2) Rutile, a natural crystalline mineral whose colour will vary
> between red, reddish brown, to black, is also made from ilmenite to
become
> the chief feed to chemical plants producing high-purity titanium dioxide
> for the paint industry. Rutile ultimate analysis is typically 93% TiO2 +
> 2.0 - 2.3% Fe2O3 in the FeO form. It should be noted that some rutile of
> commerce comes from plants making TiO2 pigments; the rutile is often an
> upgrade from cruder ilmenite ore. Rutile's behaviour in a glaze recipe
> follows that of titanium dioxide since the FeO content is relatively low.
> Rutile is sold in two grades, granular and ceramic (fine powder), and
> costs $7+/kg for 5+ kg.
> 3) Titanium dioxide is usually a bright white high-purity
> powder containing 98% TiO2, pigment grade (but some cruder TiO2
> powders are also made). TiO2 is produced chemically from one of
> titanium-containing ores, mostly ilmenite or rutile. It costs
> $10/kg (5 kg) and $7/kg (22.7 kg).
>
> Titanium compounds in Glazes
> Here is what Parmelee (1st edition) had to say about
> Titanium 50 years ago:
> "Titanium acts somewhat similarly to silicon and is added
> to glazes both for its influence on colour and its tendency to
> produce opacity since it is only slightly soluble in the melt.
> The coefficient of thermal expansion factor of the oxide (TiO2)
> is about midway in the list of common [essential] oxides...
> "Titanium is used in glazes [rutile or TiO2] to develop
> colour or textural effects. It is also an important reagent for
> the development of crystalline glazes...
> Parmelee says, depending on the base glaze, adding TiO2
> or rutile to the glaze will produce a range of colours, brown,
> green, blue, even red. He noted that TiO2 may be reduced by
> carbon monoxide to form a different oxide, one that appears red
> like a reduced copper glaze. Also, sometimes an intense blue is
> obtained in reduction, which he attributed to the formation of
> titanium nitrides. He also said that rutile + cobalt oxide
> would yield a green (yellow + blue optically blended).
> In a glaze containing zinc oxide (Bristol glaze) fired in
> oxidation to Cone 6, the actual colour yielded by iron oxide
> (0.09 moles) will go from an "intense brown" to an "intense
> green" when 0.10 moles of titanium dioxide (0.10 moles) is added
> to the glaze mix.
> Here is what Rhodes wrote many years ago in Clay and Glazes
> for the Potter:
> [The ore] rutile is used in glazes as a source of
> titanium provided the colour [from] iron is acceptable.
> Rutile gives tan or brown colour to glazes. Its tinting power
> however is weak, so more often rutile is used for textural
> effects, namely, broken colour or mottled colour. [One adds]
> 3-5% to produce such effects.
> In glazes containing boria (B2O3), rutile may cause
> pronounced streaks or spots, particulalrly in those glazes
> which are opaque and highly tinted with some other colourant,
> such as copper or iron.
> Rutile may also increase opacity when included at 5%
> or more in the glaze mix.
> [The ore] ilmenite with its higher iron content behaves
> more like iron than titanium but the larger particle sizes (80
> mesh or larger) causes specking/spotting. 1-3% is sufficient.
> Often these spots show a "halo" effect.
> Crystalline glazes, with their very low alumina content,
> and hence very fluid, are often made with zinc oxide (0.3 moles)
> and rutile, the latter helping the formation of crystals.
>
> And Frank Hamer wrote this about rutile [Potters Dictionary]:
> Rutile. TiO2. Natural titanium [IV] oxide (aka dioxide)
> with a small amount of iron [oxide] which gives it a yellow
> colour ...[which] is retained when [it] is used in glazes,
> therefore some bright creams, yellows and oranges can be produced
> in association with tin oxide, cobalt oxide, and red iron oxide.
> ...Amounts of rutile, up to 10% in a glaze, give a broken
> colouring effect due to crystallization. In association with tin
> oxide a whole variety of streaked and mottled effects are
> obtainable...
> Rutile readily produces a crystal structure in a glass on
> cooling and therefore opacity and a matt surface due to crystals
> can be produced by introducing up to 25% rutile in a glaze.
> Glazes containg 15% or more of rutile, or rutile and titania,
> are subject to phototrophy after firing. Phototrophy is the ability
> to change colour by the absorption of light [photons]. Such glazes
> darken with light and grow pale with the lack of it. This reversible
> proceess can continue indefintely.
> Rutile containing over 25% iron oxide, as FeO [iron II oxide,
> black iron oxide], is usually called by another mineral name, ilmenite,
> and this ore has a colour resonse more akin to iron oxide instead of
> titania.
>
> Here is what Rhodes wrote many years ago in Clay and Glazes
> for the Potter:
> [The ore] rutile is used in glazes as a source of
> titanium provided the colour [from] iron is acceptable.
> Rutile gives tan or brown colour to glazes. Its tinting power
> however is weak, so more often rutile is used for textural
> effects, namely, broken colour or mottled colour. [One adds]
> 3-5% to produce such effects.
> In glazes containing boria (B2O3), rutile may cause
> pronounced streaks or spots, particulalrly in those glazes
> which are opaque and highly tinted with some other colourant,
> such as copper or iron.
> Rutile may also increase opacity when included at 5%
> or more in the glaze mix.
> [The ore] ilmenite with its higher iron content behaves
> more like iron than titanium but the larger particle sizes (80
> mesh or larger) causes specking/spotting. 1-3% is sufficient.
> Often these spots show a "halo" effect.
> Crystalline glazes, with their very low alumina content,
> and hence very fluid, are often made with zinc oxide (0.3 moles)
> and rutile, the latter helping the formation of crystals.
>
> And Frank Hamer wrote this about rutile [Potters Dictionary]:
> Rutile. TiO2. Natural titanium [IV] oxide (aka dioxide)
> with a small amount of iron [oxide] which gives it a yellow
> colour ...[which] is retained when [it] is used in glazes,
> therefor some bright creams, yellows and oranges can be produced
> in association with tin oxide, cobalt oxide, and red iron oxide.
> ...Amounts of rutile, up to 10% in a glaze, give a broken
> colouring effect due to crystallization. In association with tin
> oxide a whole variety of streaked and mottled effects are
> obtainable...
> Rutile readily produces a crystal structure in a glass on
> cooling and therefore opacity and a matt surface due to crystals
> can be produced by introducing up to 25% rutile in a glaze.
> Glazes containg 15% or more of rutile, or rutile and titania,
> are subjec to phototrophy after firing. Phototrophy is the ability
> to change colour by the absorption of light [photons]. Such glazes
> darken with light and grow pale with the lack of it. This reversible
> proceess can continue indefintely.
> Rutile containing over 25% iron oxide, as FeO [iron II oxide,
> black iron oxide], is usually called by another mineral name, ilmenite,
> and this ore has a colour response more akin to iron oxide instead of
> titania.
> -------
> I hope this makes some sense to you. Til later. BFN.
>
> Tom Buck ) tel: 905-389-2339
> & snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
> (westend Lake Ontario, province of Ontario, Canada).
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