Digital BW, The Print

Robert,

I have a couple of questions on the optical brightening agents (OBA). 
I understand that the ability to fluoresce is lost with exposure to 
light and once it stops fluorescing it will appear to have yellowed 
and look duller than it did originally.

Does this decay of the ability to fluoresce occur in dark storage?

As the OBA decays or after it has decayed, does it cause any adverse 
effect on the underlying paper? Increased acidity or anything else 
that would detract from the archival quality of the paper?

Any projections as to how long the OBA's will last or is this 
directly linked to exposure?

Thanks for all the good info.

Martin Wesley


--- In DigitalBlackandWhiteThePrint@y..., chameleon@i... wrote:
> --- In DigitalBlackandWhiteThePrint@y..., Todd Flashner 
<tflash@e...> 
> wrote:
> > on 8/22/01 9:57 AM, chameleon@i... wrote:
> > > Torchon--100% wood, flourescent, L=95.11, Brightness=97.54
> > > Concord Rag--mostly cotton, non-flourescent, L=93.83, B=80.25
> > > Somerset E.--all cotton, slightly flourescent, L=95.93, B=93.06
> > > and finally...
> > > Museo--all cotton, non-flourescent, L=95.35, B=89.5 (SFA is 
made 
> > > to these same L and B specs)
>  
> > Robert,
> > Could you define fluorescence, and elaborate more on how it 
relates 
> > to brightness, and lightness, and if relevant, stability.
> > Appreciate your insight,
> > Todd
> 
> Hopefully this answers Todd Flashner's and Martin Wesley's specific 
> questions about OBAs.  The sentences in quotations are from 
Wilhelm's 
> book The Permanence and Care of Color Photographs.  Sentences 
without 
> quotes are further explanations.
> 
> "Flourescent brighteners absorb UV radiation, causing the OBAs to 
> flouresce (emit light) in the visible region, especially in the 
blue 
> and green portions of the spectrum.  If the illumination source 
> contains no UV radiation, flourescent brighteners are not activated 
> and the paper appears 'dull' or subtly lacking in brightness."--
page 
> 469
> 
> " A drawback of fluorescent brighteners in...papers is that when 
> these products are exposed to light and UV radiation over time, 
they 
> gradually lose their ability to fluoresce--in effect, the 
fluorescent 
> brightener "fades".  Thus, the paper gradually becomse faintly 
yellow 
> and less bright in appearance."--page 469
> 
> "The UV component of a "standard" museum display illumination must 
be 
> precisely defined--both for conservation reasons and because of the 
> different visual effects various levels of UV radiation have on 
> fluorescent brighteners.  Incandescent tungsten lamps emit a 
> relatively small amount of of UV radiation and have less effect on 
> OBAs in papers than daylight or fluorescent illumination.
> ...Glass-filtered quartz halogen lamps typically emit approximately 
> twice as much UV radiation as incandescent lamps. Thus, the whites 
& 
> lighter tones of prints made on papers with OBAs look noticeably 
> brighter..."--page 604
> 
> This is not metamarism, but a similar kind of effect, where a print 
> on a paper like Eclipse, German Etching, etc will look different 
> under different light sources.
> 
> Regarding the "fading" aspect of OBAs, Wilhelm's book is now about 
10 
> years old.  We are aware that there are supposedly some lightfast 
> OBAs available, but they are VERY EXPENSIVE.  Consequently, in my 
> most humble opinion, i doubt if any art paper would use these.  
THis 
> is my opinion and if I am wrong, I would hope my competitors will 
> contradict this, and elaborate on the specific OBA they use.
> 
> hope this helps somewhat,
> robert rex