From: Gordon J. Holtslander (holtsg@duke.usask.ca)
Date: 07/28/03-12:33:14 PM Z
Hi:
I'm the one who raised the issue of whether or not specific gravity and
viscosity are the same thing. From what I've read I think they are not.
There is supposed to be a simple tool for measuring viscosity. Its called
a Zahn cup. Its small cup with a very small hole in the bottom.
Viscosity is measured by timing how long it takes for the liquid to drain
out of the cup, but not drain completely - the timimg is stopped when the
fluid begins to form drops.
There are a number of zahn cups available zahn #1 zahn #2 zahn #3
Zahn cups are using in the paint industry. It may be possible to get a
zahn cup from your local hardware/paint store.
More info here:
http://www.paintcenter.org/rj/Dec02m.cfm
Hygrometers are used to measure specific gravity (density of a liquid)
Hygrometers are often used by aquarium hobbyist as an indirecty (but easy)
way of measuring the salinity of aquariums.
It may be possible to get a cheap hygrometer from a pet shop/aquarium
shop. Whether this could be used to measure the specfic gravity of gum -
I don't know.
I feel guilty having raised these issues and hinting that somebody else
should to the footwork, and not done anything - my "photo time" has
evaporated again :(
Gord
On Sun, 27 Jul 2003 stwang1@bellsouth.net wrote:
> Hi Stuart,
>
> Very strange - I replied to this message this morning but it never showed up on the list
> discussions. Did you receive it Stuart?
>
> I'll try to recap. No, I have not measured the gum I use, but my guess is that it's not too
> different from everyone else's, that is, Gum 14 plus equal amount of water. However, I
> have not used Gum 14 for years - the ones I tried all had too much preservative and were
> not very soluble after drying. I mix gum granules (tears?) 1 part with 2 parts water, plus
> very little preservative. In use, I add 1 part water to 1 part gum, add pigment to the right
> color, and then add dry dichromate. My gum "develops" in very short time, usually in 10
> minutes or less.
>
> I like to compare making gum prints to riding the bicycle: there are no secret ingredients.
> It's working out variables one at a time. When one hasn't lerned to balance on the bike, it
> looks so hard. Once he/she learned to ride, it's easy as pie. Talking about it doesn't get
> you very far. No doubt you would agree, Stuart - I saw a lot of elbow grease on your
> prints. ;-)
>
> Sam
>
> >
> > From: Stuart W Melvin <swmelvin@earthlink.net>
> > Date: 2003/07/27 Sun AM 10:58:17 EDT
> > To: alt-photo-process-l@sask.usask.ca
> > Subject: Sam...jump in here
> >
> > oooops......thanks for the info.
> >
> > To be more scientific.....we all get the gist......How thick is the stuff
> > Sam?
> >
> > corrections applied:
> > I'm wondering if you might be able to elaborate on the viscosity of the gum
> > solution you use. Have you ever measured it with a baume meter? <disregard
> > baume meter question. What
> > ratios of water to gum (solution or powder) do you prefer?. Is your
> > viscosity preference consistent or do you find you vary it for any reason?
> > How does your viscosity preference relate to your application technique? So
> > many question marks........I must admire your technique hey.
> >
> > Thanks,
> > Stuart
> >
> > -----Original Message-----
> > From: Clay [mailto:wcharmon@wt.net]
> >
> >
> > Sent: Sunday, July 27, 2003 8:18 AM
> > To: alt-photo-process-l@sask.usask.ca
> > Subject: Re: Dry Dichromate and Gum, was Re: News from APIS
> >
> >
> > Industrial viscometers are pretty pricey. But googling "viscosity
> > measurement" gives you a nifty science project link:
> >
> > http://www.science-projects.com/Viscosity.htm
> >
> > that makes me think that measuring relative viscosity would be pretty
> > simple. If one uses the same size tube and bead, then the time it takes
> > to sink would give an idea of relative viscosity between two fluids,
> > since gravity is (at least for the precision involved here) the same
> > everywhere. Maybe at the next gum printers summit, everyone can
> > standardize on a 1/2 inch diameter 20cm tube and Daisy BB pellet or
> > whatever. Then when someone asks about your coating viscosity, you can
> > just say "4 seconds". Nice and low tech.
> >
> > Clay
> > On Sunday, July 27, 2003, at 01:57 AM, Katharine Thayer wrote:
> >
> > > Stuart W Melvin wrote:
> > >>
> > >> Hey Sam,
> > >>
> > >> I'm wondering if you might be able to elaborate on the viscosity of
> > >> the gum
> > >> solution you use. Have you ever measured it with a baume meter?
> > >
> > > Sorry to jump in here, but just thought I'd interject the comment that
> > > you're making the same mistake I'd been making all my life until a
> > > couple of weeks ago, when Gordon enlightened me. A baume meter
> > > (hydrometer) measures specific gravity, not viscosity, and what's more,
> > > the two are not related to each other. This information came to me like
> > > the apple falling on Newton's head, and this is why I asked the other
> > > day the speculative question about differences in viscosities between
> > > gums. I don't know if any of us has the equipment to answer this
> > > question; if someone does I'd sure like to know about it.
> > > Katharine
> > >
> >
> >
> >
>
---------------------------------------------------------
Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
---------------------------------------------------------
This archive was generated by hypermail 2.1.5 : 08/07/03-03:34:51 PM Z CST