Digital BW, The Print

Paul,

Just wondering what the brand name of the spray you use is and 
where you can get it.  Is there an online resource that you buy it 
from?  I'd like to try coating some of my prints and was intrigued 
by your comment on the Satine paper.  Thanks.

Andy





--- In DigitalBlackandWhiteThePrint@y..., "Paul Roark" <
paul.roark@v...> wrote:
> I have found a U.S. Army Corps of Engineers Engineering and 
Design manual on
> line that is an excellent source of information on coatings.  
Chapter 4 is
> devoted to "Coating Types and Characteristics."  See
> www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-
2-3400/c-4.pdf
> 
> The two types of coatings that are of most interest to me now 
are the
> water-borne acrylics and aliphatic polyurethanes.  With respect 
to the
> water-borne acrylics the manual notes that they "provide 
coatings with
> unexcelled color retention and have excellent exterior 
weathering and
> durability properties." (p. 4)
> 
> On p. 9 the polyurethanes are discussed.  These cross-linking 
co-polymers
> work due to the affinity of their isocyanate groups for active 
hydrogens.
> The isocyanates can be either aromatic (containing the 
benzene ring) or
> aliphatic (straight chain or cyclical) hydrocarbons.  "Aromatic
> polyurethanes are prone to darkening and yellowing on 
exposure to sunlight
> because of the chromophoric nature of the benzene ring.  
Because aliphatic
> polyurethanes, by definition, do not contain the benzene right, 
they do not
> yellow or darken and are preferred for exterior use."
> 
> The aliphatic isocyanates are more expensive, but they "allow 
the
> formulation of non-yellowing, light stable, high gloss finish 
coats. The
> appearance of polyurethane coatings formulated with aliphatic 
isocyanates
> are unsurpassed in this regard by any of the epoxies, acrylics, 
or other
> coating materials."
> 
> I currently favor the polyurethanes because they are tougher 
and non-porous.
> The non-cross-linked acrylics are porous and relatively soft/
tacky.  The
> Golden technical representative led me to Hydrocote 
Polyshield, which is
> currently what I am using. It is a water-borne, single-solution, 
aliphatic
> polyurethane that, from what I have read and what the Golden 
technical
> person reports from their tests, does not yellow.  Long term 
experience will
> probably be needed to be sure of this.
> 
> While Hydrocote appears to be excellent product (one coat on 
Eclipse kicks
> the dMax to over 2, doesn't yellow the whites, and provides a 
satin/pearl
> finish that is tough enough to clean with a damp paper towel), I 
am
> searching for an aliphatic, water-borne polyurethane that has a 
higher
> solids content.  So far, I have not had any luck.  All the higher-
solids
> aliphatic polyurethanes that I've found so far are solvent-
based.  (If a
> company doesn't or won't say whether it's polyurethane is 
aliphatic, assume
> that it uses the cheaper aromatic [yellowing] isocyanates [read 
Varathane].)
> 
> If anyone knows of a high-solids water-borne aliphatic poly, 
please let me
> know.
> 
> Paul
> http://www.PaulRoark.com