From: Sandy King (sanking@clemson.edu)
Date: 10/27/01-03:48:37 PM Z
Dave,
Thanks for your comments. First, an update. With the help of Sam Wang
I tested today cyanotype and gum with the four different lights
following the same conditions earlier described for Van Dyke and
carbon. I can report that both gum and cyanotype had the same kind of
response to the different lights that was observed and reported for
carbon and Van Dyke. The speed point of gum was virtually identical
to that of carbon, which I would have expected, while cyanotype was
about two full stops slower.
>
><< 4. No surprise that the 75 watt Super Actinic was much faster (by
> over a full stop) than the 20 watt BL tubes. It also produced greater
> contrast than the BL tubes. >>
>
>Hmmm.... this is very interesting. It almost sounds like Super Actinic, by
>spectrum itself, is not necessarily faster that BL tubes. Your test result
>shows that it is more than twice faster than BL tubes, but the power used by
>Super Actinic in this case is nearly 4x of that for BL tubes (that is, if one
>person is using 1 SuperActinic and another is using 4 BL tubes, the BL might
>still be faster).
>Of course on the practical side, as we cannot squeeze 4 BL tubes in the space
>of one SuperActinic tub, it can still be useful for getting faster speed by
>using Super Actinic if we don't have 75W BL tubes (I don't know if we do),
>but it sounds like it is more power related rather than spectrum related; so
>could it be another myth that Super Actinic is really faster?
Yes, you make a good point. With the four processes that I tested the
extra speed of the Super Actinic does appear to be derived from the
fact that they are of higher wattage. This may not be so, however,
for platinum, as there are quite a number of reports that the regular
Super Actinic bulbs (20 watts at 24" and 40 watts at 48") are both
faster and produce more contrast than BL tubes in platinum printing.
>
><< 5. The *Big* surprise for me was that the GE BLB tubes were also much
> faster than the BL tubes (and of about the same contrast). In fact,
>the 20 watt BLB tubes were even faster (by about 1/2 stop) than the
>75 watt Super Actinic tubes!!! >>
>
>Sandy, is the age of the tubes taken into consideration?
>
Very important question. The BL tubes that I used for the comparison
do have some age on them, but based on the exposure times needed to
reprint negatives first printed when the bulbs were new they do not
appear to have lost any speed. In other words, a negative that I
printed in 1995 that need a three minute exposure still needs a three
minute exposure with the same bulbs today. Even so it is my intention
to test some new BL tubes to eliminate the age variable.
Sandy King
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