From: Katharine Thayer (kthayer@pacifier.com)
Date: 07/11/03-04:55:10 AM Z
Gordon J. Holtslander wrote:
>
> On Thu, 10 Jul 2003, Katharine Thayer wrote:
>
> > Gordon J. Holtslander wrote:
> > >
> >
> > >
> > > Is gum viscosity significant in gum printing?
> > > Does viscosity influence gums hardening with a dichromate?
> >
> > I think so; isn't that why instructions for gum printing generally
> > specify gum with a specific gravity of 14 Baume? I've always assumed
> > that specific gravity is related to viscosity, no?
> >
>
> I was curious so I checked this. According to this reference
> (http://www.csgnetwork.com/sgvisc.html) There is no correlation between
> specific gravity and viscosity.
>
> specific gravity is a measure of the density of a substance compared to
> water.
>
> viscosity is a measure of a liquids resistance to flow.
>
> The two are different.
>
> Denser liquids are often more viscous, but if the above is correct liquids
> with the same specific gravity could have different viscosities.
>
> It may be possible to alter the viscosity of gum arabic by changing its
> pH. Does its specific gravity change? Does it matter in gum printing?
>
> (I sound like my seven year old daughter asking too many quesions :) )
>
Thanks, that's interesting. In my defense, I never said I thought they
were the same, only that I thought they were related, but at any rate, I
stand corrected. Whether viscosity of gum can be changed by altering pH,
and whether that affects the specific gravity, and how that all relates
to gum practice I certainly don't know, but they are all empirical
questions that someone with the right equipment to measure changes in
viscosity as well as in specific gravity, a scientific bent of mind and
a yearn to know could find out and report back.
Katharine
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