| Author | Message | ||
     Felix |
Guys, just a simple question but have not found an answer yet: Which impact has the chemical composition of materials on the near IR of a visual identical colour, eg. If I have an Polyester Fabric and a Cotton Fabric and a Nylon Plastic with the same colour (shade)- how likely is it that the near IR reflection around 800 nm is different/ which varieties are possible? Thanks for your help! Cheers, Felix | ||
| David W. Hopkins (Dhopkins) |
Felix, To a first approximation, the NIR spectrum of a material is independent of color. That is, the characteristic NIR bands are found at the same position for same material made with different colors. However, intense colors may tail into the NIR, sometimes as far as 1200 nm or more. This will cause the absorbance at 800 to be affected by color in some cases. Furthermore, intensely colored or black absorbers such as carbon black absorb essentially throughout the NIR. Carbon black is used as a neutral density pigment for absorbance standards. Often derivatives help to make NIR spectral measurements independent of color. Colors can be very interesting in their effects. Best regards, Dave | ||
| felix |
Thanks a lot Dave! I am still writing on this project and have a new question: The near IR specifications of the camouflage prints of the armies are different for each country (e.g. the German Army has a different spec than the French or Australian Army), does some one knows how they select the reflection grades/ put the requirements together for the print colours? I tried to ask them but they are all pretty secretive about that... Cheers, f* | ||
| hlmark |
Felix - sounds like the kind of thing where, if somebody actually KNEW the answer, he would probably be thrown in the hoosegow for putting the information out on a public forum like this one. However, since none of us know anything about that, we can talk all we want! (Them that know can't talk, so anyone that talks doesn't know anything: its universal) But a general answer to your question, I think, is that most electronc transitions that give rise to visible absorbance have broad enough bands, and 800 nm is close enough to the visible, that a visible difference that affected the red part of the spectrum would affect this near-near-IR region as well. Some books on color technology include the effects of absorbers on this region - out to 1000 or 1100 nm. Color technology is, of course, a very heavily studied area and there is lots of information available. You main problem would be to weed out the extraneous information. That said, there are certainly differences in NIR spectra of different plastics, see for example, Spectroscopy, 9(1), p27-32 (1994), in the longer wavelength regions. From theoretical considerations, we would expect at least some of these to carry over to the short-wavelength region as well, the problem is that they would be so weak that they would be extremely difficult to detect. Howard \o/ /_\ |