Digital BW, The Print

Paul Roark wrote:

> My memory is that the fiber based papers used titanium dioxide (TO2) as a
> whitener that was referred to as a "brightener," but it does not appear to
> be the same as the OBAs in the inkjet prints.  TO2 (or at least the paint I
> have) does not fluoresce.  
> 
> When they put TO2 in the first of the RC papers, the result was cracking of
> the polyethylene barrier caused by the free radicals that are catalyzed by
> the TO2.  That is when, I believe, they started to use these dye-based,
> fluorescing brighteners in RC silver prints.  However, I'd guess they only
> used them in the RC prints, where they could be sandwiched between the
> polyethylene sheets and not washed away.  As a dye, I think an OBA might
> have been washed away very quickly in a fiber print.

TiO2 has varieties, mainly differences in the crystal 
formation, one more amorf I think. Part of the RC barrier 
problem was solved by using another TiO2 variety and the 
polyethylene was also changed. I do not believe that started 
the use of OBA between the polyethylene layers as the front 
polyethylene barrier will contain the TiO2 whitener and that 
doesn't allow much UV through, making the OBA less 
effective. Either the OBA is in the polyethylene or in the 
emulsion if it is used.

With inkjet fiber papers and matte art papers OBA will be in 
the paper and in the coating. The new Epson Exhibition has 
OBAs according to Wilhelm, I have seen it in more fiber papers.

Barite in contrast will let OBA's do their work as it blocks 
the UV less. But you need a far thicker layer of barite to 
get the same whiteness TiO2 delivers.

-- 
Met vriendelijke groeten,  Ernst


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