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  1. #1

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    Well now that I am closer to doing my first alternative process printing (cyanotype) I thought it is time to consider building a UV light source. I have been pricing out fluorescent bulbs and began to wonder if I should line the inside (sides) of the box with mirror like material.

    So ... does UV light reflect from a mirror? Is the extra effort worth the end result in my building plan?

    In the interim (after I complete the sink install), what could I use (aside from natural sunlight) as a cheap UV light source for 4x5 contact printing?

    Kind Regards
    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

  2. #2

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    White paint (or naturally white surface) would probably be a better choice - mirrors generally reflect less light than white surfaces.

  3. #3
    Ed Sukach's Avatar
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    There are two (2) distinct types of "mirrors". One is the garden variety rear-surfaced (reflective surface in back of glass - the kind on the wall in the bathroom) where light must pass through the glass twice (once going to the reflective surface, once returning). "Ordinary" window glass absorbs Ultra Violet light very effectively ... therefore much of it will be lost (actually, converted to heat).

    The other type of mirror in a "First Surface" mirror, where the reflective surface has no glass to cover it: the light will be reflected without passing through *any* glass to absorb it. These will reflect UV - and most every other wavelength of light very efficiently.

    The drawback to First Surface mirrors is their delicacy... to maintain flatness of the reflective surface, it must be *thin* - therefore, they are vulnerable to *any* slight contact. The acids from a normal fingerprint will penetrate immediately, destroying the coating. Cleaning them without damaging them is a definite problem. Before anyone starts ... yes, I know about "1/4 wave quartz overcoating" .... Expensive, isn't it ...!

    Another possibility might be plastic. Acrylics are used a LOT for optical components and do not attenuate UV much (like 93% - 97% transmission) . The problem here would be availability ... I have *no* idea where to get "rear-surfaced" acrylic mirrors.
    Carpe erratum!!

    Ed Sukach, FFP.

  4. #4
    glbeas's Avatar
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    Actually since the proposed use of the mirror is not an optical path per se but a reflector then a sheet of polished metal would be a durable and efficient front surface mirror. If you can't find a source for some good stuff try aluminized mylar or maybe cut up an old chrome plated ferrotype tin. Sheet aluminum is the easiest to use but tends to dull quickly unless coated to prevent oxidation.
    FWIW I've used those thin foam aluminized insulation sheets that builders put under siding as a cheap and quick reflector and can be cut up and assembled as needed. The uneven surface tends to diffuse the light a bit better than a smooth one would.
    Gary Beasley

  5. #5

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    and white paint would diffuse even better, and reflect more light.

  6. #6
    glbeas's Avatar
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    Quote Originally Posted by efikim
    and white paint would diffuse even better, and reflect more light.
    Of course your right about that, but not all white paints are really bright and I have no information to make me assume they all reflect UV the same. My humble opinion if using white paint, then flat white titanium would probably come closest in efficiency. Even the whitest paint has some absorbtion.
    If I were going for maximum output a highly mirrored surface would be a better bet.
    If I were going for ease of construction and cost factor the paint would win hands down.

  7. #7

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    Quote Originally Posted by glbeas
    Even the whitest paint has some absorbtion.
    and the brightest mirror has more absorbtion than the whitest paint. I no longer have the figures, and can't remember where they were, but the difference was significant. Of course the figures for UV may be different.

  8. #8

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    to get back to Grey Wolf's other question:

    Quote Originally Posted by GreyWolf
    In the interim (after I complete the sink install), what could I use (aside from natural sunlight) as a cheap UV light source for 4x5 contact printing?
    While trying to make a usable digital negative, I've been using a Phillips home solarium (for tanning your face - stupid idea!) as a reasoble source:

    4 12" tubes in a reflector, that covers an A4 page evenly at a distance of a few inches. Was aboutt £15 (about 25 US $) from a home shopping catalogue.

  9. #9

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    ... and I've remembered where I found the reflectances (in a book on building greenhouses).

    I remembered it wrong, so my apologies!

    white paint reflectance 80-90%
    glass mirror 80-90%
    polished aluminium 60-70%
    aluminium paint 60-70%
    stainless steel 55-65%

  10. #10
    Eric Rose's Avatar
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    Hey come on don't you have of those old black lights from your hippie days in the 60's and 70's?
    www.ericrose.com
    yourbaddog.com

    "civility is not a sign of weakness" JFK

    "The Dude abides" - the Dude

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