RE: Speed Point in PT/PD printing?

From: Eric Neilsen ^lt;e.neilsen@worldnet.att.net>
Date: 11/10/03-11:41:37 PM Z
Message-id: <002301c3a816$7cd92ba0$0100a8c0@NEWDELL>

Sandy, Yes that is what I meant, glass, film base or Ink jet base, basically
any thing that comes between coated paper and the light which may filter the
results. The Big benefit that I saw with Starphire was in the lower end of
the spectrum, closer to 330nm up to 370nm (top of my head here, it may be a
bit lower). I would expect to see very little or no gain due to the lack of
relevant light output unless in a BL and BLB comparisons where the BLB spike
at 360nm, and the BL has a much more bell shaped output. Bulbs such as
super actinic are already outputting in a range that no practical benefit
can be seen by using Starphire glass.

Thickness is an issue. I have a sheet of 1/2" and several 1/4" sheets and
the data certainly stacks up towards more light blocking with thicker
sheets, but it really doesn't matter unless you use the BL bulbs and large
amounts of platinum that reacts to lower wavelengths compared to palladium.

I took a quick peek at Jeffrey's page on Ferric powders, and it looks quite
good. I would check with Mike at Artcraft as a third source for powder
conversation only to broaden the consensus. He claimed that his supplier
was top notch.

Eric Neilsen Photography
4101 Commerce Street
Suite 9
Dallas, TX 75226
http://e.neilsen.home.att.net
http://ericneilsenphotography.com
 

> -----Original Message-----
> From: Sandy King [mailto:sanking@clemson.edu]
> Sent: Monday, November 10, 2003 9:10 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: RE: Speed Point in PT/PD printing?
>
> Eric,
>
> Thanks for the reference. I will get a copy of the article and try to
> determine if any of the data is relevant to my tests.
>
> I do have on hand ferric oxalate powder from two different sources.
> Ferric oxalate has been described as a "somewhat undefined substance"
> so the control check sounds like a good idea.
>
> Regarding UV blockers, do you mean things such as film base and glass?
>
> A couple of years ago, right after I finished the article on UV light
> sources that is now at www.unblinkingeye.com I acquired a few sample
> pieces of Starfire glass and made some tests with it in the small
> contact printing frames that I use to expose Stouffer 4X5
> transmission wedges. Starfire indicates that their glass transmits
> between about 3-6% more light than regular glass in the range of
> 400nm to 500nm.
>
> In my tests I was not able to detect any difference in printing speed
> with either dichromate or iron processes. However, the glass used in
> my tests was only 1/16" wide and if one were to make the same test in
> a large printing frame with 1/4" or 3/8" thick glass the results
> might very well be different because there is no doubt but that a
> fairly significant percentage of UV light is blocked by regular plate
> glass. I measured the transmission loss in the glass in one of my UV
> printers by taking a reading in UV mode through the densitometer,
> with sensitivity at 373nm. The density readings transmitted to a loss
> of log 0.16 for a 1/4" thick piece of glass. That figure represents
> a speed loss of a full 1/2 stop in printing speed, or a loss in
> transmittance of around 30%. However, even assuming that the Starfire
> glass increased transmittance at this wavelength by 5% over regular
> glass of the same thickness this would translate into a speed gain of
> only about log 0.5, or 1/3 of a stop.
>
> Sandy
>
>
>
>
>
> Sandy
>
>
>
>
>
>
>
>
>
> >Sandy, The data that I was referring to is on Page 15 of Vol. 34, 1986 of
> >the Journal of Photographic Sciences. I was mistaken, he includes
> >wavelengths down to 254nm and up to 620nm in a table giving Quantum
> Yields
> >for the Photolysis of Aqueous [Fe(c2o4)3]3-.
> >
> >I would recommend that you try several "brands" of Ferric powder to check
> >the 25% solution. If you mix B&S powder, or any powder for that matter,
> the
> >best you can hope for is a 25% solution from that powder as the ferric
> does
> >vary from maker to maker and batch to batch. I have seen speed
> variations
> >of +/- 10% when switching batches of ferric powder.
> >
> >Are you mentioning glass or other UV blockers within the test?
> >
> >Eric Neilsen Photography
> >4101 Commerce Street
> >Suite 9
> >Dallas, TX 75226
> >http://e.neilsen.home.att.net
> >http://ericneilsenphotography.com
> >
> >
> >> >> >> >>Any thoughts on this by pt/pd printers would be appreciated.
> >> >> >> >>
> >> >> >> >>Sandy King
> >>
Received on Wed Nov 12 16:09:29 2003

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