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Author Topic: Question about paper whiteners  (Read 2751 times)

Czornyj

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Question about paper whiteners
« on: January 28, 2012, 12:55:46 pm »

Lately I came across a barely used, Spectrolino+Spectroscan (the purple one!!!), that was gathering dust in a printing shop - I showed mercy, quickly grabbed this abandoned, poor little creature and gave it new loving home it deserves.

After playing with my new puppy and making spectral plots for printing papers there appeared something that puzzeled me - the spectral plots done with no filtration had a reflectance peak at ~440nm as expected. But - to my suprise - they had much lower reflectance at 380nm than the spectral plots done with UV cut filter. I wonder why the UV filtered measurement has higher reflectance level in 380-400nm part - to me this seems illogical?

Here's a bunch of samples - Ilford Gold Fibre Silk, Smooth Pearl, Smooth Gloss, Smooth Lustre Duo:








« Last Edit: January 28, 2012, 12:57:24 pm by Czornyj »
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NikoJorj

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Re: Question about paper whiteners
« Reply #1 on: January 28, 2012, 04:47:14 pm »

See : http://en.wikipedia.org/wiki/Fluorescence
To emit at 440nm, energy has (ie light) to be absorbed elsewhere, in the present case around 360-380nm.
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Nicolas from Grenoble
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Alan Goldhammer

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Re: Question about paper whiteners
« Reply #2 on: January 28, 2012, 06:01:33 pm »

Niko is right and I think all of the papers you tested have varying degrees of OBAs in them.  You can compare your plots with those that Ernst Dinkla has done HERE.  The UV cut instrument does not allow the necessary wavelength of light to hit the paper and cause fluorescence so you can't see the bump in the near visible range that is characteristic of these papers.  Depending on the type of OBA present, you may be getting absorbance in the region you are asking about which is why there is the slight difference.  I'm not familiar with this instrument, does it have a removable UV filter?

Alan
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Czornyj

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Re: Question about paper whiteners
« Reply #3 on: January 29, 2012, 04:47:29 am »

See : http://en.wikipedia.org/wiki/Fluorescence
To emit at 440nm, energy has (ie light) to be absorbed elsewhere, in the present case around 360-380nm.

This is exactly what I found particularly interesting - why is the near UV absorbed when there's no filtration, and unabsorbed nor filtered or when the UV filter is put?

Niko is right and I think all of the papers you tested have varying degrees of OBAs in them.  You can compare your plots with those that Ernst Dinkla has done HERE.  The UV cut instrument does not allow the necessary wavelength of light to hit the paper and cause fluorescence so you can't see the bump in the near visible range that is characteristic of these papers.  Depending on the type of OBA present, you may be getting absorbance in the region you are asking about which is why there is the slight difference.  I'm not familiar with this instrument, does it have a removable UV filter?

Alan, my little research was inspired by invaluable SpectrumViz. While Ernst used uncut version of i1pro, I was curious to see UV and UV-cut measurements.
Yes - the legendary Spectrolino has set of four (U, UV, P, D65) detachable filters - that's one of the reasons people still find this archaic sensor appealing.
« Last Edit: January 29, 2012, 05:12:53 am by Czornyj »
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NikoJorj

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Re: Question about paper whiteners
« Reply #4 on: January 29, 2012, 05:44:29 am »

This is exactly what I found particularly interesting - why is the near UV absorbed when there's no filtration, and unabsorbed nor filtered or when the UV filter is put?
I'm getting out of my knowledge zone, but I'd say that UV absorbtion is triggered by excitation (maybe by a higher, more specific frequency radiation).
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Nicolas from Grenoble
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Czornyj

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Re: Question about paper whiteners
« Reply #5 on: January 29, 2012, 06:00:08 am »

I'm getting out of my knowledge zone, but I'd say that UV absorbtion is triggered by excitation (maybe by a higher, more specific frequency radiation).
Thanks Niko - I also came to the same conclusion by deduction, it seems to be the only reasonable explanation of this behavior.
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Marcin Kałuża | [URL=http://zarzadzaniebarwa

Ernst Dinkla

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Re: Question about paper whiteners
« Reply #6 on: January 29, 2012, 06:27:20 am »

This is exactly what I found particularly interesting - why is the near UV absorbed when there's no filtration, and unabsorbed nor filtered or when the UV filter is put?


Anything you would expect in fluorescence will happen without a UV-cut filter but depends on the light source and the sensor characteristics and above all what the software does with the sensor signals after that. As I understand it the UV-cut results extrapolate the plot below 420 NM from the measurements above 420 NM or alike. So do instruments that do not even have light into the UV range and are without any filter. Graeme Gill has written on that subject.


met vriendelijke groeten, Ernst
Shareware too:
330+ paper white spectral plots:
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
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Alan Goldhammer

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Re: Question about paper whiteners
« Reply #7 on: January 29, 2012, 09:55:16 am »

I'm getting out of my knowledge zone, but I'd say that UV absorbtion is triggered by excitation (maybe by a higher, more specific frequency radiation).
You got this backwards.  It is the absorption at the UV wavelength that triggers the fluorescence.  Not every molecule is capable of fluorescing.
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