Judy Seigel wrote:
> Eric, you say a real benefit for BL bulbs from the Starphire. I realize
> your experience is with pt/pd, but I'm curious if the benefit would be
> mostly in speed, or in "the curve." I imagine if the curve is affected it
> would not be the same effect in different media, but wonder if you would
> hazard a guess on any of the above. (I have the sheet I removed from the
> NuArc because it made gums worse... might try it with the BLs. But isn't
> worth it for speed because gum exposure there is only 1 to 3 minutes to
> begin with.)
>
> Thanks,
>
> Judy
Judy, There are many aspects of the pt/pd process that effect the curve; ratio of
metal salts in coating solution, ratio of ferric to metal salts, RH, specific
paper, etc. The advantage that one get from a combination of Starphire with BL
lamps is that the more of the UV light produced is allowed to pass through to the
paper. I don't have my charts in front of me from PP&G and Spectral outputs to
give %'s and #'s, but the standard green glass block a higher percent of UV
light. This is only a few percentage points at 380 and up but is substantial at
360nm and lower. The output curve of the BL lamps peaks at 350nm and gently
slopes down in both directions. The sensitizer is reactive over a large range,
but the platinum and -palladium are not equal reactive across that range. Since
palladium and platinum have different curves both effected by UV output and Rh, I
can not speak to the effect for "the" curve. However, the largest effect that
maybe seen is on the 350nm to 300nm side of the UV output / glass transmission
combination. OK , I found my charts. Starphire transmits 35.5 % of UV light @
300nm where Standard transmits .3%; @310nm 53.1% Star and .8% Standard; @320nm
67.9% Star and 9.1% Standard,; @330nm 79.2% Star and 34.4% Standard; @340 86.1%
Star and 61% Standard; @350nm 89.1% and 77% . At 360nm and above it stays at
about 91% for Starphire and 86% for Standard.
Relative speeds for Platinum and Palladium change as the out put goes from 350 to
320 with platinum being slightly faster. However, the big difference is in the
speed in relationship to Rh. If you print at High Rh, 60 to 70% palladium is much
faster, and conversely platinum prints faster at low Rh 15% to 25%.
So , can you see why I can not say that "the" curve can be substantially effected
by the change in glass? It would depend on what coating solution one uses and at
what Rh range is used. What we can see however, is that more UV rays reach the
sensitized paper with Starphire than with Standard glass and that the additional
UV energy will increase the exposure that the paper receives.
I don't know the sensitivities curves for the different mediums covered on this
list, so I can't say that other processes would benefit from a change to
Starphire. I would guess that some would benefit from the unused UV energy that
standard glass block out, but it may not be enough or have side effects that are
not desired, as those you have spoken about. One should research the glass, UV
light output of their unit, and sensitivities of materials used before buying into
a system as best, better, the ultimate answer.
And what the heck, I have not seen much information on the B-270 that David shared
with us. I can see that Starphire allows approximately 70% at 325nm or nearly
twice as much as B-270 which would lead me to not use it, or perhaps not buy it.
I might use it if I had a sheet to see what it can do.
Cheers
best guesses from EJ Neilsen
-- Eric J. Neilsen 4101 Commerce Street, Suite #9 Dallas, TX 75226 214-827-8301 http://home.att.net/~e.neilsen
This archive was generated by hypermail 2b29 : Tue Jan 11 2000 - 12:10:47