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Blue light on Black cloth?

Discussion in 'Lighting and Electrics' started by Schniapereli, Dec 13, 2007.

  1. Schniapereli

    Schniapereli Active Member

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    Why is it that when you shine blue light on black clothes, that they look dark red?

    I am guessing it has something to do with the dye. I remember hearing something about there being two kinds of black paint, red base, and blue base. I am wondering if this applies to dye and is the cause of this effect.
     
  2. propmonkey

    propmonkey Well-Known Member

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    yep 2 different dyes. theres red black and blue black.
     
  3. gafftapegreenia

    gafftapegreenia CBMod CB Mods

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    The reason this occurs is because of UV light, not because of visible blue light. This also works under black light. I'm guessing your using a halogen source with your blue gel? Since high wattage halogen lamps put out quite a bit of UV, the low transmission of the blue gel lets it act as a blacklight. Fluorescent tubes also put out a good amount of UV to make them suitable as blacklights. I've been in some "old fashioned" museums where the fluorescent tubes in their displays have completely destroyed artifacts, clothing and paper. That's why the incandescent blacklight bulbs you buy at the party store don't work that well, they put out little UV. Fun stuff.
     
  4. Schniapereli

    Schniapereli Active Member

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    That makes more sense.

    I can't find any information onlie about red-black and blue-black dyes.

    If anyone has any information that would enlighten me, that would be greatly appreciated.
     
  5. Footer

    Footer Senior Team Senior Team Premium Member

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    Heres the deal, black dye does really make something black, in order to get something black you have to add either blue or red to it. I just dyed a white scrim black 2 weeks ago, in order to do it I used 8 bottles of black dye and 3 bottles of navy blue dye, without the navy blue the piece would not look black, it would look purple.
     
  6. Schniapereli

    Schniapereli Active Member

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    Interesting...

    And either red or blue will do the trick?
     
  7. JD

    JD Well-Known Member

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    One other thing, blue gels usually have a BIG band pass in the red region! Take a look at the Apollo book, which is nice enough to provide spectrum transmission charts. Check out AP 4250 for example! Most blues are that way so that they are wide open as they head into the IR "heat" region.
     
  8. sclausenETC

    sclausenETC Active Member

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    Hi guys -

    Having lit a lot of dance, I can speak to years of experience of getting different results with "black" fabric and blue light. It's not just dye, but fabric type that can affect what you see. Natural fibers tend to look more black (have more blue/green in the dye) and artificial fibers (nylon, poly) tend to go red. So, depending on the manufacture of the garments, you may have black or brown or red on stage when that blue light turns on. It's a real pain. If you have any influence at all with your costume designer (or choreographer), try to get them all wearing similar fabric types so that at least you get the same color behavior across all the folks on stage. :)

    My $0.02...

    Sarah
     
  9. tomed101

    tomed101 Active Member

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    It becomes very obvious during the concerts at school with the choir. They always walk on in blue light and because it is a very large choir (270 members) they are onstage in blue for quite a while before we go to white. The choir shirts look red under blue and the pants look blue. You can always tell who has skimped and not bought the proper choir uniform, they always stand out:rolleyes:
     

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