I found this from the Collectors Club of Chicago:
Stamp hinges are one of the philatelic products most used by stamp collectors. When the original stamp hinge test results were received, second tests were conducted on the most popular name-brand stamp hinges to confirm the original results; no differences were found. Not one brand of stamp hinge manufactured in the United States was found to be non-acidic.
The Swedish-brand hinge, Novofold, was alkaline. In order to determine how one manufacturer could produce a glassine hinge that was acid-free, the independent laboratory was engaged to conduct further tests on the Swedish hinge, comparing the analytical results to one of America's leading hinge brands, Fold-O-Hinge. Separate tests were requested for the glassine, and for the glassine's adhesive. The laboratory test procedures were as follows:
Prior to the testing procedures, the samples were conditioned at a standard Technical Association of the Pulp and Paper Industry (TAPPI) temperature of 73ºF and 50% relative humidity; all of the requested qualitative and quantitative test procedures were performed in accordance with standard TAPPI testing methods.
A cold extraction pH test was prepared from the two samples using 1.0 gram sample + 70 ml distilled water. The mixture was covered with a watch glass, and was allowed to stand for one hour at room temperature. The mixture was stirred three times at regular intervals to insure the total wetting of stamp hinges, and the total solution of the mucilage adhesive.
After one hour, the liquid portion was decanted into a second 100 ml beaker, and the liquid samples were saved for their pH determinations.
The remaining stamp hinges were washed three times with 10 ml portions of distilled water; the washings were discarded. 70 ml of distilled water was added to the beakers with the hinges, and the samples were allowed to stand for one hour at room temperature preparing for pH determinations
The pH readings were conducted on the first wash water, and on the water extract of the washed hinges, with the following results:
Stamp Hinges pH Readings
Sample Test No. 912-19 912-21
Hinge Brand Fold-O-Hinge Novofold
pH Before Aging 5.8 7.1
pH After Aging 5.4 6.7
pH pH Unaged Reserve 0.0 0.5
pH Aged Reserve 0.0 0.5
pH of Adhesive Solution 5.4 7.2
pH of Washed Paper 6.1 7.1
Glassine paper is a smooth, transparent paper manufactured from chemical pulps that have been heavily machined. This type of paper is grease proof, and when waxed, is practically impervious to air and vapors. Sample 912-21 (Novofold) is a transparent glassine type of paper. Under normal manufacturing conditions, the glassine should be slightly acidic, but it appears that some type of unknown alkaline process was employed to manufacture the Swedish hinge.
Conversely, Sample 912-19 (Fold-O-Hinge) is a semi-glassine, parchment-type paper that has not been subjected to as much machining as a true glassine. Parchment-type papers of this type are less transparent than glassine, having a white opaque color. The Novofold and Fold-O-Hingeadhesives were analyzed, and both were starch-based adhesives
The following test procedures were conducted to determine the taste, peelability and adhesion of the stamp hinges. Due to the variability of the adhesives found on postage stamps, the tests were performed on hinges affixed to album pages only, and not to stamps.
Prior to the testing procedures, the samples were conditioned at a standard TAPPI temperature of 73ºF and 50% relative humidity; all of the requested qualitative and quantitative test procedures were performed in accordance with standard TAPPI testing methods.
Thirty hinges were selected at random from each of the name brand sealed packages of hinges. The hinges were manually mounted individually on an alkaline-grade stamp album page, being moistened with saliva.
At the time of moistening the hinge with saliva, the taste of the adhesive was recorded: Pleasant, Satisfactory or Starchy.
After one week of storage at room temperature and humidity, the hinges were manually peeled from the album page, and observed for ease of removal, completeness of removal, and tearing.
On the basis of the observations, the hinges were rated for Peelability (Poor or Good), Hinge Strength, and whether the Hinge Tears, or Does Not Tear. If the result determined "10% tear", this indicates that 10% of the hinges that were affixed to the page tore off without leaving a residue on the album page. Peelable indicates that all the hinges were removed from the album page without a residue.
If the pH value is 7.0 the sample is neutral. pH values lower than 7.0 are acidic, and pH values higher than 7.0 are alkaline. It should be noted that a pH 4.0 is ten times more acidic than a pH 5.0, and one hundred times more acidic than pH 6.0.
This is based on data sourced from the United States National Bureau of Standards, and the widely used permanent paper standard America National Standards Institute (ANSI) No. Z39.48
Hinge Brand Test No. pH pre- Aging Peel and Tear* Taste Adhesion
CMC 918.43 4.8 P Pleasant Good
Dennison No 4 912.16 5.4 50%T Pleasant Good
Dennison No 64 912.17 5.1 50%T Pleasant Good
Dennison No 54002 918.24 5.6 P Pleasant Good
Fold-O-Hinge 912.19 5.8 50%T Pleasant Good
ExactaPhil 918.21 5.0 10%T Pleasant Good
G & K Hobby 912.20 5.6 PT Satisfactory Good
Stanley Gibbons 922.1 5.7 75%T Starchy Good
La Mor 918.22 5.3 100%T Pleasant Good
NovoFoldfactory Good 912.21 7.1 PT Satisfactory Good
Scott 918.23 5.8 50%T Pleasant Good
Western Stamp 912.18 5.12 P Pleasant Goodhttps://www.collectorsclubchicago.o...ic-products/