I have made the same experience as Janet. Moreover ph-meters seem to be
unable to measure pH propperly in deionized water, unles dirt has
solubilized and re-establishes coductivity of the water.
I use ph-papers by Merck (the kind which does not bleed) in a combination of
several types and with a standardized method as well for measuring pH in the
liquid as for measuring surface pH. With a pH meter you have to use a real
drop of water in order to make them work, and the error margin is still
rather big with surface measurements. With the papers, the textile does not
become copletely wet, and you still get good readings (sometimes only in
tiny spots on your paper; so it takes some experience, but it works fine).
Make sure you use water with a pH of 7 (so don't use deionized water, which
is always below seven). E.g. tap water or "evian" bottled water when you are
working on site.
There has been an interesting student paper at the "Fachhochschule Köln"
(Diane Lanz, ca. 1992?)comparing exactness of ph-measuring methods
(surface-diode; wet extraction; ph-papers) and the papers turned out to be
the much better equivilant to the wet extraction than the surface-diode.
 
Hope this helps. Sincerely, Karin von Lerber
Karin von Lerber
 
______________________________
 
Karin von Lerber
Prevart GmbH
Konzepte für die Kulturgütererhaltung
Oberseenerstrasse 93
CH-8405 Winterthur
Telefon + 41 (0)52 233 12 54
Fax + 41 (0)52 233 12 57
e-mail: [log in to unmask]
www.prevart.ch
 
----- Original Message -----
From: "Janet Farnsworth" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, August 20, 2002 6:44 AM
Subject: Re: Portable pH meters
 
 
> I would just like to add a word of caution: My experience of pH meters
> is very mixed and I suggest that before you buy a flat electrode meter,
> you test it on all the surfaces you might want to measure the pH of, [in
> case it need to make the surfaces so wet it is unusable] and ask about
> recalibration and indeed about drying out problems.
>
> I would be very interested in the results of your research; I am sure
> that pH meters have improved since I last looked at them.
>
> message <[log in to unmask]>
> , Ellis, Shirley <[log in to unmask]> writes
> >Hello,
> >We are looking for a portable pH meter with a flat electrode that can
read
> >the pH of textiles or paper, or liquids.  Does anyone have or know of one
> >that they can recommend?
> >
> >thanks,
> >
> >Shirley
> >
> >Shirley Ellis, MAC, CAPC
> >FSO/Conservator
> >Department of Human Ecology
> >B-20 Human Ecology Building
> >University of Alberta
> >Edmonton, Alberta T6G 2N1
> >ph (780) 492-7678  fax (780) 492-4821
> >email:  [log in to unmask]
>
> --
> Janet Farnsworth
>