Optical brighteners - and their fading

During all my fade test I made some observations which are not so much printer/Epson or ink related but deal with the optical brighteners in the photo papers in use and with the influence of ozone onto the fading.
It is not possible for me to separate the influence of UV radiation and/or ozone at all, I only can make some assumptions to be discussed later. And I don't have any means to measure ozone, the level, the dose over time which all makes the testing done by Aardenburg or Wilhelm research in their test chambers so expensive.
Optical brighteners, as an additive to the coating of inkjet papers, are colors which are invisible under regular light. They are supposed to get active when exposed to UV light, light with a wavelength close to the visible blue/violet range, they create a light blue color which is supposed to increase the perceived whiteness of a paper. It is used heavily in copy papers as well for this purpose, typical office light from neon tubes emit still some enough of such UV light to create this effect as well.
When buying photo papers you don't know what you get, the OB content is rarely mentioned in product descriptions. The optical brighteners can cause some problems in the profiling process, you can measure the color patches with an instrument which is sensitive to this near UV spectrum or not - using a filter in the spectrometer filtering the internal light source. And profiling software can include or exclude such readings, the inclusion of optical brighteners got pretty complex over the last years .
Let me show you - to start with -


a 10 Euro bill under such UV light, you can get very cheap lamps - flashlights like this one
https://www.amazon.com/Creazy-UV-WF...qid=1494518365&sr=8-27&keywords=uv+flashlight
There are various print elements showing up under UV light to check the validity of this bill.

This is a shot of three photo papers under such light

The top violet one is an HP premium glossy photo paper, the middle and lower ones in lighter cyan are
Aldi/Sihl and Aldi/Netbit papers , I'm using all of them for various printouts. The HP paper does not contain any OB's , the other papers a lot. You barely see any difference under normal light, the Sihl paper looks a bit more yellowish, the Netbit and HP papers both show a neutral white. But when I look to the fading targets currently running outside the optical brighteners are gone after a week or two - they fade faster than any ink on the paper. This raises the question why those OB's are used at all if they fade that quickly ?
I'll show you some more observations in the next days.

@Ink stained Fingers, can I please have all of your waste used €10 notes when your finished testing...

oh well, there is another strange effect - they are fading away - even secretly out of my purse.....

If you see a minus 'b' value, say -5, in the L*a*b* measured values for the paper, this usually means OBA is present

yes and no, depending on your spectro - you are getting different readings with or w/o UV cut filter on a paper with OBA's. My problem is that those OBA's fade away pretty quickly and I'm thinking to ignore them completely. Why should the profile provide compensation for them when they are gone after a short while.

I'm viewing one of the targets with the scotch tape now with UV light

The left part is kept as the reference in the dark, the OB is clearly visible with its light cyan, the right
part was exposed to the outside, sun etc , the OB's are gone and the paper shows the blue violet of the lamp. There are some smaller lighter cyan spots in between, that's the areas covered by the scotch tape slowing down the fading of the OB's, as well small stripes at the top and bottom which are covered by the clamping rails to hold the targets.

I was referring to the manufactures quoted Lab values, not my own!

For those seriously interested in the properties of inkjet papers, the site of Dutch Master Printer Ernst Dinkla contains a wealth of information including the spectral plots of over 700 different inkjet media types. A veritable treasure trove of valuable information on the subject.

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm

rs

there is quite some information available about these optical brighteners, yes, when you dig through to the datasheets by paper manufacturers you'll find that the paper white level is listed, or you find a remark 'contains optical brighteners', but you are not made aware that this is only a temporary property of that paper.
These are samples fans of photopapers by Tecco and Fotospeed under UV light

You see a wide variety of papers, glossy , matte, silk, fabric, Baryt etc with lots of OB's or none and every amount in between.
When you look to the Fotospeed samples fan, to the top layers you see this

the small sheets are slightly bending upwards for a small amount and providing a small gap at the edge so that the ozone could circulate between the layers and deactivated the OB's starting from the edges.
And as with the inks - the OB's are fading slower on some photo papers than on other papers, the Aldi/Netbit paper performs better in this respect than the budget cast coated LogicSeek LS180 paper I'm using in various cases.
And there is another little detail with this swatch - the top cover sheet is not protected by other sheets but the optical brighteners are active nevertheless, it appears to be covered by a PE foil , and the text is printed on top probably with some solvent ink , aqeous inks won't adhere to such a surface.

I'm surprised how fast the optical brighteners fade under typical exposure situations. I'm not sure yet how to include that into the profiling process, I think I'll print the target patches, whatever paper I'm using, and place the prints into the sun for a week or so to let them pre-age for a while - to let the OB fade away - mostly at least, and only then scan them for the profile calculation. Adn I'm surprised that the HP Premium Plus Glossy Photo (CR674A) paper does not use any OB's, this is the only glossy photo paper so far I have seen like that, all other glossy papers, Sihl, Tecco, the Fotospeed papers above , LogicSeek, Labelheaven use OB's quite heavily, the OB usage does not depend on the pricing of these papers.