alnovo@inwind.it
Date: 03/25/02-01:39:08 AM Z
> On 22/03/2002 08:02 Judy Seigel wrote:
>
> You're mixing 1.698% solution ????
Yes, for analytical purposes such precision is needed. "Normal" laboratory balances are capable to weight 1/10 of a *milligram*.
> I've measured, for instance, silver nitrate on a piece of paper (as
> described) -- maybe 17 or 20 g -- in 100 cc water, which would have made
> for some close calls with all that sluicing. On some papers I'd see tiny
> black specks after the paper sat around in the light for a few days... on
> a smooth vellum or tracing paper I didn't. I took that to mean all the
> chemical had slid off. But I expect now you'll tell me some remained just
> too small to see :(.
Silver nitrate usually has very large and heavy crystals, so it is also very easy to handle, but when you are weighting very light stuff as, for example, hydroquinone lot of it can still remain on the paper.
> Actually, seriously, I begin to think (having tried some REALLY accurate
> tests with cyano) that perfect control -- even I bet in a lab -- is a
> chimera... there's always something -- tho maybe in a clean room with
> large quantities, and everything, eg., electricity, under strictest
> discipline you get closer.
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!
Alberto
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