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I need a dye that is "highly colored" or intense. I want to put it in water and flow the water in the form of a liquid sheet that is around 100 microns thick. A number of spray nozzles use this principle to produce droplets. The liquid is first formed into a sheet that breaks down after a few milliseconds into droplets.

The issue is that at such thin thicknesses, colors often disappear even if they look very intense in a tank. I'll be working with around 0.2 gallon per minute to 0.5 gallon per minute flowrates, so something that hopefully can be added in relatively small quantities. But more important is that the dye is non-toxic and environmentally safe.

Thanks for any suggestions.

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  • $\begingroup$ There is many env-safe-nontoxic dyes, but If by env-safe is meant easily degradable, it gives limited options. Hot candidates are plant dyes, like anthocyanins, but it may be difficult to separate them from plant matrix. It may be possible to bye purified ones. $\endgroup$
    – Poutnik
    Commented Nov 13, 2020 at 7:14
  • $\begingroup$ I can't address the environmental issues, but would a fluorescent dye work better? You could illuminate your device with UV light, and the emitted light should show up better than a non-fluorescent dye. $\endgroup$
    – user137
    Commented Nov 13, 2020 at 10:47
  • $\begingroup$ Go to the next supermarket, and buy some of these dye solutions specially made for food coloring. $\endgroup$
    – Maurice
    Commented Nov 13, 2020 at 10:48
  • $\begingroup$ @user137 I've considered fluorescent dyes, but I'm going to be shooting high speed video (10000 fps or more) and a lot of light is required. Are you aware of any fluorescent dyes that fluoresce under LED light? $\endgroup$
    – rdemyan
    Commented Nov 13, 2020 at 21:52
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    $\begingroup$ I did some checking and you can get UV LED flashlights with 100 LEDs. Ebay has them cheap. Typically, these are 365 nm or 395 nm. These are serious light sources. And, yes, sunlight works fine and you can use a simple Fresnel lens to concentrate the sunlight. Or use a light pipe: a glass rod drawn down somewhat to act as a light funnel. If I remember correctly, some commercial cleaning products have fluorescein in them. Best of success with your project! (I think I will buy a couple of those UV LED flashlights and some fluorescein.) $\endgroup$
    – Ed V
    Commented Nov 14, 2020 at 13:40

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Many organic dyes which are fluorescent can be carcinogenic like the famous Rhodamine dyes. You can try a couple of tricks. One of best inks, at least for demonstrations, is the yellow highlighter's ink which fluoresces bright green in water (see my photo below). If you can shine a bright white LED or a bright blue LED, it will fluoresce very strongly. You can use an optical filter in front of the camera that can block blue light and let the green and longer wavelengths in. With that you can increase the sensitivity.

Note that fluorescence intensity is directly proportional to the incident light intensity in dilute solutions.

Figures

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  • $\begingroup$ @ M Farooq: Thank you for your response. So it sounds like fluorescein should provide a strong fluorescence under a bright white LED light. I'll be using a 300 watt equivalent LED light bulb. $\endgroup$
    – rdemyan
    Commented Nov 14, 2020 at 2:49
  • $\begingroup$ Yes. Fluorescein is best in alkaline media. Better to use optical filters, shine blue light over the liquid and block blue light on the camera. You need cut off filters. $\endgroup$
    – ACR
    Commented Nov 14, 2020 at 4:58
  • $\begingroup$ This is a good time of year, a few weeks past Halloween, to buy heavily discounted “glow in the dark” chemiluminescent light sticks. Carefully cut open, they have the various fluorescent dyes used to produce the light stick colors. The old ones had the dye in the glass ampoule: I still have three of them. Newer light sticks may have the oxidizer (hydrogen peroxide) in the ampoule. Either way, the dyes are available for testing with whatever set up is ultimately used. For fluorescein, I would use the disodium salt. And the filters are essential. $\endgroup$
    – Ed V
    Commented Nov 14, 2020 at 17:52

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