Re: Ri:Re: Measuring

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From: Judy Seigel (jseigel@panix.com)
Date: 03/26/02-12:59:23 AM Z


On Mon, 25 Mar 2002, alnovo@inwind.it wrote:
> A really accurate test on cyanotype deals with: temperature and relative
> humidity of the room, accuracy in the preparation of the solutions and
> quality of water, type of paper, its seizing, coating and drying
> processes, time, intensity and spectrum of the light source, time,
> temperature and pH of the washing process, time, relative humidity and
> temperature of the drying process, environmental characteristics during
> the visual inspection (intensity, Kelvin temperature and distance of the
> light source, colour of the room walls, colour of the observer's
> clothes), and finally, "mood" of the observer ;-)
>
> (Is the hair sufficiently splitted?)
>
> I bet that only coating can account for almost 50% of the variance!

Thanks Alberto... I found this quite reassuring... that is, perfect
measurement is not going to happen outside a lab, and a high-end one at
that, so I can relax.

However, your "bet" about the coating confirms my general hunch. Which was
why, when I tested the bulb spacing I estimated overall *look* of a
full-size sheet of paper rather than "reading" 21-steps.

There's also the fact that the 21-steps, even if the coating were perfect,
would have to be the same ones in the same place, since they're different
one from another, & there are slight differences in light from spot to
spot ... HOWEVER, speaking of *BETS* I'm not sure but what Sandy King owes
me -- was it a million dollars?

I remembered from those tests of bulb spacing that the 21-steps LOOKED
quite different at the different heights -- didn't pay much attention
since the step tablets were incidental & I figured the 30-second exposure
was too atypical to mean much. But when Sandy INSISTED that exposure at
all distances would be pretty much the same, I decided to try a better
quality test.

The short answer is, as far as I could tell, being as precise as I could
(eg, leaving bulbs on the whole time to eliminate start-up & maintain
temp, also using same 2 step tablets in same places, & timing the drying
period, all exposures 6 minutes, etc.) they are and they aren't the same.

Could still take a couple more tests, which I might even do, but
meanwhile:

At distance of 1-1/2 inch, 3-1/4 inch, & 5-1/2 inch, the top tone visible
is pretty much the same -- that is, the blue rose to the same number at
the 3 distances (which is, as far as I'm concerned, absurd, like being
captured by Martians). HOWEVER, the character of the shadows is not the
same. There are a lot of details, more than you want to know, but in
effect, at 3-1/4 inches the range was longer than at greater or lesser
distance.

That is, instead of 8 steps as on the other two, there were 9 steps,
because the d-max at 3-1/4 inches is greater & the separation thus becomes
better.

Is that worth a million dollars? (D-max is greater I GUESS, because at
1-1/2 inches there's less solarization from the over-exposure of close up
at the same time that the bottom steps block up from over exposure -- and
there's also less saturation at the greater, 5-1/2 inch, distance). I
picked those distances because I had supports to take the glass to those
points. And yes.... I did it a couple of times & got same results.

Interestingly, the two 21-steps I was using turned out to be quite
different in density.... I noted after the fact that they were made at
different times, as shown by the different logo at the top, although I
don't know if difference in same batch is ever as great. Anyway, the
different density of test strips take the different distances differently.

- Judy


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