Re: Opacity of digital negative substrates, was Re: Gum a la Sam Wang

Judy,

In response to your response to Sandy's response to.... regarding your doubts
whether Pictorico might be a tad slower than other film.

With PT/PD, I've done test strips with clear Pictorico film and a Stouffer's
step tablet. Sam Wang suggested this as a method of determining base
exposure when printing using digital negatives on any film substrate substrate. It
works very well, and I have done it many times with different combinations of
PT/PD, Na2, various papers, and even tried it on my undershorts. It's the
best method I have found for determining your base exposure time. If anyone
can see folly where I tread, please enlighten me.

Here is what I did at Sam's suggestion. It is so simple that you wanna
whack yourself on the forehead and scream "Why didn't I think of that!".

I took the Stouffer step tablet and laid it over the edge of a piece of clear
Pictorico film in such a manner that the edge of the strip of Pictorico
bisected the Stouffer step tablet. I then made an exposure of roughly 2-3 times
what I thought was was my ballpark exposure for this mix of PT/PD on the given
paper with a NUARC—to make sure I would end up with at least two steps
merging. Once developed and dried, I examined the test print with my own eyeballs
and looked for the point where two dark steps of the printed Stouffer merged.
I found it. I celebrated. I even double checked with a desnitometer
appropriately set to reflective mode. The merging of the two steps was exactly
one step lower for the portion that was also covered by Pictorico—in every case.
  I should add here, of course, that this was the infamous Stouffer #T2115 21
Step Sensitivity Guide (granted, the uncalibrated version, which costs more),
which measures exactly .15 log transmissive density per step give or take a
lumen or two.

At least for PT/PD and God only knows what other alt process, I would have to
say that I am convinced beyond a shadow of a doubt and I would even bet the
life of my first-born....well maybe my second-born.... that clear Pictorico
film measures about 1/2 stop or .15 UV density. When I measure it with a
transmissive densitometer, I get exactly log .04 transmissive density, from both
sides (just in case the ceramic coating caused some weird, unidirectional
abberition), which is a fair amount less than .15 log density.

Now perhaps I should qualify all the above with a disclaimor that the UV
density suggested by this series of observations would apply to that spectrum of
UV light that caused my PT/PD to do its trick. I won't go into my undershorts
at this writing—for that contact me off list.

What Sandy is referring to is clear Pictorico film, not Pictorico film or any
other film that has silver or ink or fingerprints or dust or chicken soup
smeared, sprayed or gicleed on it. This is an important point to remember when
using Pictorico—it is a great substrate, but it does add overall density to
your negative.

Now if we are going to talk about how inks block UV light, that's a whole
other discussion, but not the one that Sandy is referring to.

Kindly submitted to this august group by your humble servant this Year of Our
Lord, 2003. ;)

Mark Nelson

In a message dated 11/23/03 11:00:52 PM, jseigel@panix.com writes:

> Although I've done various tests on Pictorico, I haven't printed with it
> enough to speak with assurance of its printing qualities (tho I still
> doubt it's slower than film as seems to be the consensus here -- tho maybe
> it was the black ink that blocked less UV than silver blocks, even though
> it read the same on the Macbeth.???)
>
Received on Mon Nov 24 00:32:59 2003