Re: gum and humidity (was: Measuring humidity)

[Sandy King <sanking@clemson.edu>]

At 8:06 AM -0700 9/29/06, Katharine Thayer wrote:
> (This discussion seems to be ranging across 
> several threads; I pity anyone who tries to 
> follow it later)
>
> On Sep 28, 2006, at 9:11 PM, Sandy King wrote:
>
> > Temperature and humidity are major issues for 
> > carbon printing. Sensitivity is much higher at 
> > 85ºF and 90% RH than at 70ºF and 35% RH. This 
> > absolutely has to be factored in when printing.
>
> Yes,  but this example confounds humidity with 
> heat again.   For gum at least,  sensitivity is 
> also higher at 60F and 90% RH than it is at 60F 
> and 65% RH (35% is a range I never encounter, so 
> I stayed within a range I'm familiar with so I 
> can speak from my own observations).

Well, I don't see any reason not to confound them 
since they are both different variables. There is 
no question but that the RH with the temperature 
held constant has  big effect on sensitivity. 
This can range from almost no sensitivity at RH 
of 20% or lower, to very great sensitivity at RH 
of 90% or higher. However, the oppose it also 
true. If you hold RH constant  and vary the 
temperature you will have more sensitivity at 90º 
F than at 50ºF. When I first started printing 
carbon I carried out testing of this type to help 
me better understand how to get consistent 
results, and although I don't have the data any 
longer, I am reasonably certain the above is 
correct.

Sandy