RE: Wet & Dry Exposure


John Melanson (john@audiologic.com)
Sun, 01 Aug 1999 21:01:40 -0600


I think the weight change of the paper would be an interesting measure of
how wet.

I tried an experiment today on testing how wet is a wet exposure.

I was coating a 8.5X11 sheet of cranes. Weight initially 5.3 gms (Colorado
dry, 10% RH). Weight after humidification 5.8 gms. Weight after coating
and drying 6.0 gms.

With and accurate balance, or using several sheets, you could start with
bone dry paper, bring to room humidity, then humidify, coat, etc. The
weight change, compensating for the amount of solids in the coating, would
tell how much moisture is in the paper at each step.

This would allow a way to standardize discussions.

Just an idea.

John Melanson

> Carl et all,
>
> Had some time during printing today. I have results from a preliminary
> comparison of what will be called "wet" and "dry" exposure.
>
> "Wet" exposure means that the relative humidity of the coating was at
> ambient and rather high when exposed. Drying was accomplished by
> blowing ambient air over coating until just dry. This coating was
> prepared and dried at an ambient RH of 65% (temp 82F).
>
> "Dry" exposure means that the ambient RH was lowered and the print dried
> by blowing air with medium heat over the coating to dry as much as
> practicable. This coating was prepared and heat dried at an ambient RH
> of 51% (temp 82F).
>
> Two prints were made and compared.
> Paper was Crane's lot # 5302 (the one in question)(AKA parchment
> Business card stock; AKA Cover 90; AKA pltinotype)
> Coating was 9 drops FO (27%), 6 drops K2PdCl4 solution (19%), 3 drops
> K2PtCl4 solution (24%), 1 drop Ammonium Dichromate solution (0.25%)
> Paper was humidified
> Coatings were applied by brush and covered enough area for a 4x5, a
> 21-step, and boarders.
> Coatings were dried as above
> Exposed for 6 minutes with BL type lamps.
> Developed in Potassium Oxalate
> Rinse/Pre-clear in water bath
> Cleared with phosphoric acid baths for total of 30 minutes
> rinsed in buffered water, washed, dried
>
>
> OBSERVATIONS:
>
> PRINTOUT
> + The "wet" print had much more print out. The printout was very dark
> for the blacks and very high contrast. I suspect that this is a
> determining factor in the separation of shadow values. (See findings
> below)
>
> DARK AREAS
> "dry" print ==
> + Has a darker boarder, which is also warmer and has more apparent
> depth and substance.
> + Does not show any solarization effect.
> + Speed point - difference from step 2 to 3.
> "wet" print ==
> + The dark area (boarder) is a more neutral black and appears flatter.
> + Shows some solarization effect of boarder and steps 0, 1, 2, and
> possibly 3 with reflected light only. Transmitted light does not show a
> solarization effect. Whether this is really solarization is not known.
> + Speed point - could be from step 3 to 4 since step 3 may be off and
> definite difference from step 4 to 5. (Steps are about ½ stop.)
>
> CONTRAST
> + The "dry" print seemed to reach a zone VIII between steps 15 and 16
> with clear discrimination of 17 and 18.
> + The "wet" print seemed to reach a zone VIII around step 17 with clear
> discrimination of 18, 19, and some discrimination of 20.
>
> VALUES AND TONALITY
> + The "wet" print mid and upper values have a warmer color while the
> lower values are more neutral.
> + The tones look smother in the "dry" print.
> + While both prints have good shadow detail, the "wet" print seems to
> have better discrimination in the shadows (especially in bushes and tree
> trunks).
> + Even though over all contrast is about the same and the "dry" print
> has better blacks, the "wet" print shows more contrast (or
> discrimination) in the dark areas of the image (not in the 21-step).
>
>
> FINDINGS:
>
> The "wet" print is about 3/4 stop faster.
>
> The "wet" and "dry" prints have about the same contrast.
>
> The "dry" print has more depth and substance while the "wet" print may
> be solarizing.
>
> The "dry" print has warmer dark values; the "wet" print has warmer mid
> and high values.
>
> The "wet" print has better shadow separation.
>
>
> COMMENTS:
>
> If what appears to be solarization could be stopped, the "wet" print
> could be superior. If a better printout could be obtained with the
> "dry" print, then it could be superior. As they are now either method
> can produce a great print. It becomes a mater of trading nuances (some
> of them not so tiny.)
>
>
> DISCLAIMER:
> Keep in mind that other papers or chemistry may behave differently.
>
> --
> Jeffrey D. Mathias
> http://home.att.net/~jeffrey.d.mathias/
>



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