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In search of an opaque fabric that allows free air movement — Parallax Forums

In search of an opaque fabric that allows free air movement

idbruceidbruce Posts: 6,197
edited 2012-04-10 19:41 in General Discussion
Hello Everyone

I need a fabric that is opaque but allows free movement of air. Is there any such fabric?

I want to surround a couple of heat lamps with a curtain of opaque fabric that will allow for heat dissipation. The heat lamps will be used in a photograghic darkroom environment.

Bruce

Comments

  • Erik FriesenErik Friesen Posts: 1,071
    edited 2012-04-09 14:38
    It would be easier to use some black anodized aluminum baffles, or similar. Why not use a small oven element, they put out much more heat in the infrared range, and not so much light. I can't think of any fabric opaque enough.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2012-04-09 14:38
    The usual material for this is speaker cloth of some form. I think you'll still get some light shining through, too. It's mostly "opaque" under normal light to prevent seeing the inner workings of the speaker enclosure. I'm also not sure how well the cloth will stand up to heat, though.

    Consider light baffles, which is how open-door darkrooms work (or worked; do people still use them??). It's basically a Z-bend opening, painted flat black. Light has a very hard time getting through. You don't need a lot of space if it's just air.

    -- Gordon
  • Mike GreenMike Green Posts: 23,101
    edited 2012-04-09 14:43
    The short answer is no, there is no such fabric. In order to get free air movement, you need openings in the fabric, the larger the better. Such openings let light get out. What you need is a baffle arrangement. Light mostly goes in straight lines, air doesn't have to. You can make baffles out of non-fabric materials. Wood works. Plastic works. Metal works. Even opaque, mostly solid fabric works. You'd want to use a flat black paint, possibly something flocked to prevent reflections. Overlap the baffle walls so the light doesn't get through. You could use cylindrical baffle layers with slots for airflow, maybe 3 or 4 layers with the distance between layers similar to the width of the slots. Another option might be to use a fan to exhaust the hot air.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2012-04-09 14:46
    idbruce wrote: »
    The heat lamps will be used in a photograghic darkroom environment.

    As a separate side, I'm guessing this is so the darkroom can be heated? So as you know most photographic emulsions are sensitive to infrared. Infrared heat lamps, producing little or no visible light, will light-strike photographic film and papers. In darkrooms the heating must be indirect. Assuming it's for heating the room, you want some kind of forced-air heating from a different part of the building. You can pipe something in through a vent.

    -- Gordon
  • idbruceidbruce Posts: 6,197
    edited 2012-04-09 14:55
    Thanks so much for the ideas gentlemen, baffles it is. A truly fantastic idea. I have several large vents with deflected openings that will work perfectly, except that I will have to make the enclosure from wood as compared to fabric, but that's okay.

    @Gordon - I am only using the heat lamps to briefly heat up my chemicals to the proper temperature. I will be placing the heat lamps under the chemical trays.

    @Erik - I need the element to quickly dissipate heat to prevent further heating of the chemicals. The heat lamps work very well.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-09 15:17
    GordonMcComb wrote: »
    So as you know most photographic emulsions are sensitive to infrared. Infrared heat lamps, producing little or no visible light, will light-strike photographic film and papers.

    I while back I had some infrared film I needed developed. The film could be developed with the same chemistry used for color slide film. The problem was the machines used to develop color slide film used an infrared light to count the sprocket holes. This infrared light didn't expose the normal color slide film but would expose the infrared film.

    I ended up having to buy the chemicals and develop the film myself. It was actually kind of fun. I had never done the darkroom thing before.

    So apparently not all film is sensitive to infrared light (not that Gordon had made such a claim).

    Sorry for the sidetrack Bruce.

    I used a large insulated cooler to help keep the water bath a constant temperature. The insulation really helped keep the temperature stable.
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2012-04-09 15:46
    Duane Degn wrote: »
    I while back I had some infrared film I needed developed. The film could be developed with the same chemistry used for color slide film. The problem was the machines used to develop color slide film used an infrared light to count the sprocket holes. This infrared light didn't expose the normal color slide film but would expose the infrared film.

    I ended up having to buy the chemicals and develop the film myself. It was actually kind of fun. I had never done the darkroom thing before.

    So apparently not all film is sensitive to infrared light (not that Gordon had made such a claim).

    I'm wondering what kind of slide film this was. Ektachrome (E6) is somewhat sensitive to near infrared, though the cut off is at about 750-800nm as I recall. For many years Kodak sold a special "professional" color film with extended IR sensitivity. It was developed during WWII for aerial work. Was this the film you used? E6 process is about the only one you could do at home. Kodachrome is blind to infrared, but the K14 process is nearly impossible for mere humans to do, or at least that's what Kodak always said. In fact, I'm pretty sure no one does it now, or if they do, it's a small specialty lab that probably charges a fortune per foot. Do you recall the emulsion and process you used?

    (It's too bad about Kodachrome ceasing production. I always thought it was the best color film ever, even ignoring Paul Simon's song. I have Kodachrome slides taken nearly 40 years ago that are as vibrant today as they were then. My Ekta slides are slowly weathering and losing color saturation.

    -- Gordon
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2012-04-09 15:51
    idbruce wrote: »
    @Gordon - I am only using the heat lamps to briefly heat up my chemicals to the proper temperature. I will be placing the heat lamps under the chemical trays.

    These are plastic trays, right? I guess that rules out an immersion heater. It might emit some IR, but you'd take it out of the soup and unplug it before processing any photos.

    Not that I've ever done this myself, but I've seen guys heat up their developer in a microwave. They keep one in the darkroom, and remove the light. Being in California, I've never had to do that myself. I also always used liquid developer and fresh-batched each time, using warm water. For the stop and fixer I never cared what the temp was, though I imagine in places like Indiana where it actually snows now and then you'd want to avoid very cold liquids.

    Ah, the memories of working in a chemical darkroom!

    -- Gordon
  • idbruceidbruce Posts: 6,197
    edited 2012-04-09 16:23
    Gordon - This is actually developer for the photoresistant film on positive acting presensitzed printed circuit boards. This film is very sensitive to the temperature of the developer. If the developer is too cold, the film will not develop and if it is too hot, all the photoresist basically just dissolves off the board. The developer must be between 100 and 110 degrees fahrenheit, with 104 degrees appearing to be the optimal temperature.

    Bruce
  • idbruceidbruce Posts: 6,197
    edited 2012-04-09 16:35
    It is basically a non-issue, since I will not have any boards just laying out. I am just trying to be a little over-cautious.
  • TubularTubular Posts: 4,709
    edited 2012-04-10 13:14
    There are thermal blankets that are designed for conducting heat away, available from companies like Bergquist

    They wouldn't allow air flow, but perhaps they would solve the problem.
  • Mark_TMark_T Posts: 1,981
    edited 2012-04-10 16:51
    idbruce wrote: »
    It is basically a non-issue, since I will not have any boards just laying out. I am just trying to be a little over-cautious.

    I can't believe anyone would go to the bother of sensitizing a photoresist to longer wavelengths than necessary - its complex dye based chemistry - I suspect the heat lamp is safe (but you can test this easily if worried). Usually violet/UV is needed for photoresists as only the weakest chemical bonds are affected by the red end of the spectrum. That's why we don't get sunburn under plain tungsten bulbs (tungsten-halogen emit a lot more blue/UV being run hotter).
  • kwinnkwinn Posts: 8,697
    edited 2012-04-10 17:27
    It sounds like you are concerned with minimizing temperature overshoot by making the light baffles as light as possible. If this is the case you may want to consider using two or more aluminum foil layers painted flat black and mounted on wood frames. Non overlapping holes are simple to cut and the foil sheet can be glued or stapled to the wood frame.
  • idbruceidbruce Posts: 6,197
    edited 2012-04-10 18:25
    @Mark_T
    I can't believe anyone would go to the bother of sensitizing a photoresist to longer wavelengths than necessary - its complex dye based chemistry

    I don't know where that came from, but okay. I am using DATAK Premier positive acting boards, which are exposed with a standard incandescent bulb. The heat lamps are also incandescent, but they are used for simply heating the etchant and developer. The developer must be between 100 and 110 degrees fahrenheit. I want to block the light from the heat lamps, just in case I need to warm up the developer or etchant while any protective coatings have been removed from the PCB material.

    Please refer to the datasheet for further information.
    http://www.philmore-datak.com/datakpos.html

    @kwinn

    Yes the objective is to eliminate temperature overshoot. As mentioned in another thread, and I probably should have posted it here as well, considering that the etchant and developer trays are considerably translucent, I must also block the light from going upward and shooting through the trays. I remember seeing this in an old photography book many years back, where they wrapped a light bulb in aluminum foil for some odd reason. I believe I will attempt this as a light shield. And I am well aware that it could considerably shorten the life of the bulb, if it does not burn out almost immediately. But hey, it is worth a try.


    Bruce
  • TubularTubular Posts: 4,709
    edited 2012-04-10 18:50
    Other thing that occurs to me is to use a silicon heater pad or strip to do the heating without introducing "light", eg these

    Sometimes (depending on the thermal masses involved) you can measure the resistance of the heating element itself (while de-energized) to deduce the temperature at the interface
  • idbruceidbruce Posts: 6,197
    edited 2012-04-10 19:41
    @Tubular

    That was a pretty good idea, and it probably would have worked very well, however, at this point, my path is already well established. With the exception of any light remedy, I have already purchased the heat lamps, lamps sockets, building a platform, etc... The heat lamps work very well, in the fact that they do not overshoot the temperature. Simply turn the switch off and the temperature stops climbing. I have not tested the aluminum foil idea yet, but I think it will work.

    Bruce
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