Re: Coating prints with polyurethane wood finish

From: Loris Medici <mail@loris.medici.name>
Subject: RE: Coating prints with polyurethane wood finish
Date: Thu, 02 Feb 2006 08:22:51 +0200

> Dmax increased by 1 stop means the darkest part of the image is 0.3 unit
> darker for the coated specimen, when compared to the uncoated one

Ok, that's what I hoped you meant (though I don't see the unit "stop"
customarily used for density measurements), and that's somewhat
expected. In modern silver gelatin prints, the Dmax is largely
determined by the paper surface. Glossy gives the highest Dmax (in
reality, this comes with the cost of increased annoyance of
reflection).

> The polyurethane I'm using is water based - can provide the CAS numbers
> of the ingredients later.

I think the actual polyurethane products are proprietary
mix. Polyurethane is a very indefinite name; it is a generic name for
a very broad class of polymers of a wide range of compositions. The
name sounds like many-urethanes to laypersons, but that's not even
close. The polyurethane has urethane-chain links but the relative
amount of urethane is small, and the other parts are left up to the
chemical engineer's decision.

So, for this type of products, I would definitely consult experts
(like paper conservators) and closely follow their recommendation to
the product number. One major manufacturer of this class of polymers
is Bayer MaterialScience of Dormagen, Germany.

I thought that there was a professional conservator on this list...
(Possibly 3 or more of them!)

Ryuji
Received on Thu Feb 2 01:02:17 2006