7 comments for “Ozy and Millie: In the long run

    • Paint is harmed by light. Some kinds of paint are more durable than others; some acrylics will show slight changes of color after a single flash exposure. Textile dyes will fade and fabric will weaken over time.

      • I’ve never run into that with paints. Admittedly I worked with gouache and oils, rather than acrylics, but friends who did acrylic didn’t seem to have the problem of light fading unless left in sunlight.

        Older pigments from centuries past were generally from mineral sources mixed with a binder such as oil or albumin and wouldn’t be readily touched by UV. Vermillion, for example, came from crushed cinnabar. Shades of yellow (orpiment) to red (realgar) came from arsenic.

        Neither Xenon flash tubes nor magnesium sponge/powder broadcast UV, at least not that I could see (I can see down to about 250nm). Sunlight and a number of mercury-based light sources such as fluorescents have a mix of UVA and UVB (glass stops UVB and fused quartz stops UVA).

        Textiles rot in UVA and UVB. The main body of the atmosphere stops UVC, so unless one is in a jet at high altitude, it’s not present.

        • even if you’re not dealing with UV light (never mind where different people argue UV starts and visible light ends,) the shorter wavelengths of light cause lasting damage. Where I work, a lot of people would be happy with nothing shorter than 430nm.

          I recall an article by one of the Canadian agencies where they indicate light-damage potential increases significantly around 3electron volts (which is somewhere in the blue range, never mind the violet/UV.)

          I also recall seeing a video by the Royal Institution — one of their Christmas Lectures — showing blue light having enough energy to “activate” one of their demonstrations. (It’s at about 24:30 in the video here: http://richannel.org/explosive-science )

          So yes, while the flash photography may not harm the stone — textiles, paints, or coatings on the stone may be harmed. Although one flash being the same as a decade of light is a bit off…

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