Antique Medicine Bottles

Why does old glass bottles turn shades of purple?

old glass bottle9.thumbnail Why does old glass bottles turn shades of purple?
vainfilly asked:

If i place a old bottle in the sun, how long until it would show purple?... is there other ways to get this same effect?

2 Responses to Why does old glass bottles turn shades of purple?

  1. Yamson

    Apparently only glass with the element manganese in it will turn purple in UV light — and quite often there isn’t enough UV light from the sun to do it. So to answer your question, it may never turn purple because it doesn’t have manganese in it, and on top of that, leaving it in the sun may not have enough UV radiation to do it anyway.

    Under UV radiation, the manganese combines with the oxides in the glass to create MnO2, a compound which absorbs light in the visible spectrum except that which creates the color purple. Therefore, as light passes through the glass, it appears purple.

    FYI, glass manufacturers started using manganese in the 1860s, but mostly stopped by 1915 when they started using selenium. Both elements improved glass clarity.

  2. WhiteWolf359

    Clear glass bottles exposed to sunlight for long periods of time turn purple because they are exposed to ultraviolet and cosmic rays. The UV rays “dye” the bottles. I understand that if you stand a bottle in the sun, it can become “purple” in about six months’ time, but I’ve never tried it. You could also try shining a “black light” light bulb on the bottle, but since no light bulb approximates the millions of jules of sunlight, it would take much longer, maybe thousands of years, for the tiny light bulb to dye the same bottle.

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