RE: BL vs BLB tubes for cyanotype

Eric,

Your statement that the Appendix in Dick Arentz' book on speciality
glass concluded that there was no advantage to Starphire glass does
not accurately represent what is stated. And I am very familiar with
the Appendix since I wrote it. Here is what I did and wrote.

1. I compared the transmission of plain float glass with that of
Starphire glass (both in 1/16" thickness), using a UV transmission
densitometer with peak at 373 nm and bandwith of 60 nm. The Starphire
had slightly better transmission, but based on analysis of the data
the increase in speed would have only amounted to about log 0.5, or
1/3 of a stop in glass 3/16" or 1/4" thick.

2. I tested several processes for speed, using a Stouffer test
tablet, comparing results in a contact printing frame using 1/16"
thick plain float glass and 1/16" Starphire glass. And I specifically
tested several different mixes of palladium and platinum. After
looking at the results I found there was no advantage at all to
printing with the Starphire glass, but allowed that use of thicker
glass in the contact printing frame might give different results,
perhaps up to 1/3 of a stop faster.

3. I concluded with the comment "it is almost certain that one could
reduce printing times slightly by replacing the ordinary plate glass
in our vacuum frames or contact printing frames with speciality
glasses that allow the transmittance of a higher percentage of UV
radiation," but that in my own cases I had considered this carefully
and "determined that it is not worth the trouble."

I conclude from your comments that you believe one of the advantages
of Starphire glass is that it allows "more lower end light to pass,
such as 320 nm to 360 nm." However, many Pt./Pd. printers are using
light sources which are totally absent of radiation in this range.
For example, if you look at a SPD chart (spectral power distribution)
of the Philips Super Actinic tube, which is very popular among
Pt./Pd. printers, you will see that there is virtually no radiation
below 360 nm, and none at all below 350 nm. So if anyone finds a
significant increase in printing speed with the Starphire glass using
the SA tubes it must be due to greater transmission in the upper UV
range, not in the lower end.

Sandy

>But the light out put of the two type is not same. I recently acquired Dick
>Arentz' book on platinum printing to have as a reference when students show
>talking about it, as well as to read Mark Nelson's bit on digital negs. The
>very first page I opened just happened to be about specialty glass; UV type.
>He went on to talk about Starphire (misspelled Starfire) and concluded it
>had no advantage, based primarily on wave lengths above 400 nm. It has very
>little if any advantage at those wave lengths, which a simple review of the
>transmission data would tell you. Certain glass like Starphire, allow much
>more lower end light to pass, such as 320 nm to 360 nm. If the material you
>are using is sensitive to those wave lengths such as platinum vs palladium,
>then adding light in those wave lengths will speed up your process.
>
>
>I don't think that that much change would be anticipated. BLB typically
>output mostly between 350 and 370 with the peak at 360. While the BL has a
>much broader output, but also peaks at 360. Your glass would need to be
>blocking light right at or near 360 to see such a dramatic change.
>
>Was your stack of paper constant? And as Sandy pointed out light output will
>fall off after a warm in period.
>
>
>Eric Neilsen Photography
>4101 Commerce Street
>Suite 9
>Dallas, TX 75226
>http://e.neilsen.home.att.net
>http://ericneilsenphotography.com
>
>> -----Original Message-----
>> From: ryberg [mailto:cryberg@comcast.net]
>> Sent: Tuesday, November 15, 2005 5:10 PM
>> To: alt-photo-process-l@sask.usask.ca
>> Subject: Re: BL vs BLB tubes for cyanotype
>>
>> Michael,
>> Well, I suppose my glass could be extra transparent to UV, but it is
>> the same glass that I used with the BLB tubes which took 15 minutes.
> > Charles Portland OR
Received on Wed Nov 16 08:44:19 2005