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Old 25-07-05, 02:23 PM
Alessandra Kelley Alessandra Kelley is offline
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Default UV+Titanium White=Disaster?

I just read an Associated Press story (Chicago Tribune, Monday, 25th July, section 4, page 1), "Buildings May be Ally in Battle Against Smog", which has troubling implications for artists.

The gist is that coating buildings and bridges with a thin layer of Titanium Dioxide (aka "Titanium White") reduces pollution because it "can become highly reactive when exposed to ultraviolet light." Through photocatalysis "organic compounds are broken down into carbon dioxide and water." This happens when the Titanium dioxide "is applied in a very thin layer, or in microscopic particles."

This sounds disturbingly like what we do in tempera painting, laying down very thin layers of Titanium Dioxide pigment, which is, of course, in microscopic particles, adjacent to organic compounds (both egg and many other pigments).

My grasp of chemistry is basic, so maybe somebody more knowledgeable can help me out here, but . . . Does this mean that a reaction between UV light and Titanium Dioxide pigment will slowly eat away at the organic compounds (i.e. the egg and any organic pigments) in tempera paintings?
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Old 25-07-05, 08:44 PM
turlogh turlogh is offline
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Default Re: UV+Titanium White=Disaster?

Quote:
Originally Posted by Alessandra Kelley
My grasp of chemistry is basic, so maybe somebody more knowledgeable can help me out here, but . . . Does this mean that a reaction between UV light and Titanium Dioxide pigment will slowly eat away at the organic compounds (i.e. the egg and any organic pigments) in tempera paintings?
In theory, lead white pigment should react to the sulphur in egg yolk by turning black. In reality, lead white in egg tempera paintings from the Middle Ages and Renaissance is fine (more transparent than it was originally, but not black). I don't know why.

I'm not a chemist, either, but I've never heard of problems with titanium white. Since titanium white has been used as a pigment since early in the 20th century, I think we'd know by now about any signficant interactions with other pigments.
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Old 26-07-05, 09:26 PM
Alessandra Kelley Alessandra Kelley is offline
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I have actually seen more than one medieval painting where the Virgin is sitting next to a vase of black lilies. I don't know why all the white hasn't gone black; perhaps it has something to do with thicker layers of more protective media.

At any rate, according to Keiko Mizushima Keyes, a paper conservator, "Titanium dioxide . . . is a pigment that came into use in the 1920s, and subsequently has come into wide use as a filler to increase the brightness and opacity of industrially made papers. This substance can cause photochemical degradation of cellulose." (Emphasis mine)

And according to Ulrike Diebold of Tulane University's Department of Physics, "By far the most actively pursued applied research on titania is for its use for photo-assisted degradation of organic molecules. TiO2 is a semiconductor and the electron-hole pair that is created upon irradiation with sunlight may separate and the resulting charge carriers might migrate to the surface where they react with adsorbed water and oxygen to produce radical species. These attack any adsorbed organic molecule and can, ultimately, lead to complete decomposition into CO2 and H2O." (Emphasis mine)

This does not look promising.
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Old 29-07-05, 08:33 PM
realgesso realgesso is offline
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I've read quite a bit on this subject. Here's my understanding of what's refered to as "Photocatalytic degradation" :
TiO2 will absorb more than 99% of all UV radiation that strikes it. The UV light is than temporarily transformed into electronic energy resulting in an electronically excited TiO2 particle, the majority of this energy is quickly transformed again into heat energy which subsequently dissapates from the paint film's surface. However, the problems lies in the fact that for every million light absorbtion events, up to .0001% of the electronically excited TiO2 particles can become chemically reactive with surface water and/or oxygen and form hydroxyl and superoxide radicals. These radicals are free to migrate from the pigment's surface and react with the organic compounds.

Something to note, however, is that TiO2's ability to prevent UV from breaking down organic compounds directly outweighs the problems associated with photocatalytic degradation.
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Old 14-08-05, 05:05 AM
Marc Kingsland
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I was talking to Ian Maginnis at W&N about this sort of effect a few months ago.
Basically the answer is that in most artists paints, the titanium dioxide particles have been coated to prevent this sort of reaction.
I think the only titanium dioxide pigment left uncoated is that which is intended for gouache. I think because it's more opaque.
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Old 23-11-05, 05:13 PM
Camilla Camilla is offline
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Since most paintings live their life indoors - that is, behind windows which let only a small fraction of UV-light through - my guess would be that this effect is much less pronounced in ET than it would be on a sunlit bridge.

I suppose this would apply to oil paint as well. But hasn't titanium white oil paint been used for windows and doors for years with good results - also outdoors?
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Old 23-11-05, 06:28 PM
Alessandra Kelley Alessandra Kelley is offline
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Errhm, no, not exactly. Since lead was eliminated from house paint (a good thing), instead of the tough, long-lasting but poisonous films of lead paint, we have titanium white which eventually grows powdery and crumbly.

Also, I believe it is a myth that window glass blocks uv light.

Also also ... No offense to Realgesso, who is knowledgeable and helpful, but even 0.0001% of Titanium Dioxide molecules is still an awful lot.

Still ... After I started this thread, I tried painting without Titanium. It was awful. Zinc White -- although lovely and useful -- just can't do what I need it to. I am troubled by certain aspects of Titanium, but I can't paint without it.
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Old 03-01-06, 10:44 PM
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Dimitris C. Milionis Dimitris C. Milionis is offline
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Quote:
Originally Posted by Alessandra Kelley

Also, I believe it is a myth that window glass blocks uv light.
UV exihist in all forms of glass ware, the level of penetration and/or protection level differs

http://www.ukiyoe-gallery.com/sunfade.htm

see this link I found that will drive you nuts, but fading is not actually related to the UV factor but the heat build up on the surface of the paint!
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Old 05-01-06, 09:04 PM
Alessandra Kelley Alessandra Kelley is offline
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That's a really interesting link. It looks like UV-protection glass may stop UV, but even regular visible light can badly fade inks. I think the point there, however, is that older inks used on antique ukiyo-e prints can be badly affected by sunlight even with UV glass. The newer reprints, with more archival inks, hold up better.

I like to think we as artists are using more permanent pigments.
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