Digital BW, The Print

djon43 wrote:

> Harman asserts they're alone with baryta. 
> 
> Is some clay other than baryta used? 
> 
> Baryta's only advantage vs other clays(the reason Kodak used it for
> Kodabromide)was its natural whiteness. It was called "pipeclay" in the
> Royal Marines of the 18th century, used to whiten uniforms (just a tidbit)
> 
> The "fineness" would be irrelevant, since it's ground to whatever
> degree is necessary.

I wouldn't call Barium Sulphate/Sulfate a clay. It isn't pipe 
clay. It is more an ore. Barium Sulfate should be called 
Barite or Baryte and not Baryta which is Barium Hydroxide. The 
last you wouldn't like to use as a coating as it is a strong 
base and water soluble.

http://en.wikipedia.org/wiki/Baryta

http://en.wikipedia.org/wiki/Barite
http://www.sharlot.org/archives/photographs/19th/book/chapter_2.html

The last link describes the use of Barite as a whitener for 
paper since the 1820's and as a whitener for photographic 
paper since1880.

Some of us have swallowed it mixed in water before x-ray takes 
in hospital, it increases contrasts.

One wonders whether that Harman name is used as a reference to 
the Harman Barite mine in Virginia.
http://www.mindat.org/loc.php?loc=104721&ob=4

The usual clay as used in offset paper coatings is kaolin 
which may be used in one form or another in inkjet coatings 
too. The fineness can be very relevant if the crystal 
structure + the stacking of the particles defines the 
absorption of fluids. That kaolin or China clay or pipe clay 
is the base for porcelain as well and used by soldiers too for 
cleaning and whitening. Kaolinite is a  kind of aluminium 
silicate, the particle structure and stacking of particles is 
important in the absorption behaviour so there are different 
methods for manufacturing the coating powder.

http://en.wikipedia.org/wiki/Kaolin

There's a difference in use too in inkjet papers I guess. The 
Barite is there in the first place as whitener + to make the 
paper more opaque, the clays like Kaolin are there to absorb 
the ink and by that reduce bleeding next to being (less) white 
and opaque. Harman refers to a silica coating as well on that 
paper. The Barite was used in analogue papers before RC 
papers, as a first coating on paper to get the white surface 
and on top of that the silver gelatine emulsion, in inkjet 
papers that would be the ink receptive layer of micro 
ceramics/silica/kaolin or whatever on top. The extended tone 
range if there is any is probably achieved at the paper white 
end if it is the result of the Barite. Overall the coating 
could have been improved next to the Barite addition. Whether 
that Barite is so special has to be seen, titan dioxide has 
been used for decades as a whitener for RC and normal papers 
and does a good job, opacity being better. Innova's Fibaprint 
uses titan dioxyde.


Met vriendelijke groeten, Ernst


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