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

Judy Seigel wrote:

>
>> One of the obvious problems in carrying out this kind of test with
>> gum is that you would need to be able to weigh accurately extremely
>> small amounts of dichromate. For example assuming that you took as
>> your norm 10ml of coating solution, to run tests with sensitizers in
>> the 1% to 10% range would require that you be able to measure
>> accurately from as little as 0.1g to as high as 10.0g.
>
>To put it mildly. And, as noted, no particular reason to do so. Or none
>that I can see.

Judy,

The reason should be obvious. Protection of *your* environment. The
way you work results in pollution of the environment with more
dichromate than is necessary for the application. Just do the figures
and and show me if I am wrong,

>
>And I seem to have lost the message where you wrote that the pictorico
>measured .15 per step on the densitometer... apparently claiming that
>that meant it was slower than the Stouffer. But isn't the Stouffer .15
>per step??? You said something about comparing by having them overlap. I
>couldn't follow that. Would you explain again-- ?

I think you have confused my original message with a subsequent reply
by Mark Nelson. I wrote that the UV density of clear Pictorico base
is about log 0.15. You can verify this by reading the base of
Pictorioc with a densitometer in UV mode, or you can test it
empirically as Mark suggested. Either way you get the same result.
The substrate of Pictorico has UV filtration of about 0.15.

Best,

Sandy

>
>TIA,
>
>Judy
>
>>
>>
>> >Somewhere along in here Sandy made an analogy to carbon printing, or
>> >anyway dichromate exposure with gelatin. I HATE to be wrong in print, but
>> >I have an idea that analogy doesn't hold. I don't see how you can talk
>> >about *speed* for a gum print without the variable of pigment
>> >concentration -- or at least some reference to that -- or at least how the
>> >"speed" is to be figured, unless of course the referent is gum +
>> >dichromate tone only.
>> >
>> >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.???)
>> >
>> >HOWEVER, that issue aside, how do you measure "speed" when you're adding
>> >pigment -- say, SO MUCH pigment that the steps block up, so you only have
>> >3 instead of 5 or 6? Would you measure by the top step? But even then
>> >you couldn't count just the substrate, you'd still have to factor the
>> >variable of pigment & amount of pigment.
>> >
>> >?
>> >
>> >J.
>>
>>
>> --
>>
Received on Thu Nov 27 00:40:28 2003