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Acid Test Pen, Folder test question

This topic contains 11 replies, has 8 voices, and was last updated by Profile photo of Paul Hagan Paul Hagan 1 year ago.

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    Profile photo of Kelly Revak
    Kelly Revak

    I made an alarming discovery with my acid test pen the other day, that I would love to get some clarification on if anyone has wisdom to share.


    I have been using Smead Organomics Recycled folders, which were advertised as “acid free”. Indeed a test with the acid test pen gave a “green” response color indicating a neutral PH. ¬†However I have just discovered that over time (15 minutes to an hour) this mark is fading to an acidic “yellow” response. In all other papers I’ve tested with this same pen, the color/ph indicated is clear within a few seconds and does not change over time.

    So my question is.. are these folders neutral ph or acidic? And what does a gradually changing PH indicator mean??


    many thanks,

    Kelly Revak

    Profile photo of Ron Kley
    Ron Kley

    A great many paper products (e.g., most ordinary copy paper) is essentially acid-free because the manufacturers add calcium carbonate to neutralize the acidity of the wood pulp that is their raw material. They do this not to keep museum people happy, but to protect their machinery from the long-term effects of the acidic lignin in wood fiber.

    Many products soid as “acid free”¬† have a neutral or even alkaline pH, BUT they still contain lignin which, over time, will yield acidic decomposition products. Only those psper¬†products that are both acid-free AND lignin-free should be regarded as being safe for long-term archival use.¬† (Some acid-free paper products that are “buffered” with added calcium carbonate will counteract the acid-generating decompsition of lignin — for a time, but not forever.

    I can’t imagine any paper product going from neutral to acidic in a matter of minutes, but the rate of such a change would depend upon a number of factors including the species of wood in the pulp and the original pH of the product, as well as the temperature, humidity and chemical composition of the environment.

    Note also that perspiration, skin oils and some cosmetic products may be mildly acidic. So if any of those things got onto acid-free paper, and a pH test pen was then used on the spot, it might register an acidic reading on a spot that had been neutral only minutes previously.

    Bottom line — go for acid-free AND lignin-free paper products, but expect them to be significantly more costly.



    Profile photo of Kelly Revak
    Kelly Revak

    Thank you for that informative response!

    Is there a way to test if materials are lignin-free?

    RE: anything getting on the folders to result in an acidic reading.. these are fresh out of the box and unhandled. It is particularly strange to me because the reading stays as “nuetral” for 5-10 minutes, and then gradually fades to “acidic” over time after that. The mark is fully in the acidic range by 20 minutes or so. Quite strange.

    Profile photo of Ron Kley
    Ron Kley

    Hi Kelly —

    I don’t know of any simple test for lignin. Your best bet is to ordermaterial that’s specifically described as both “acid-free” and “lignin-free” from reputable suppliers.

    I rely upon¬† Gaylord in the course of my contractual curatorial and archival work for museums and historic sites, and have been very happy with their products and service., but they’re not the only supplier by any means.

    If you do by products that are acid-free but not lignin-free in the interest of economy, it would be a good idea to set samples aside and to test them on a regular basis — about once a month for a year, and once a year…forever, or until they give an acidic reading with a test pen.

    Buffered paper products cost a bit more than simply “acid free” products (but lots less than lignin-free stuff), and they will retain their non-acidic pH for a longer time…but not forever. Periodic testing of samples would still be prudent.

    Good luck!





    If the amount of items in your collection are big enough, you may want to really test these paper based product in order to verify their real content of lignin.

    Basically, its about to take a clear small paper fibers sample, mix it with a solution and see it trough microscope. Lignin will take an specific colour in contact with the reactive solution.

    Its not something hard to do, but as any lab test it should be performed by somebody with previous experience, since you need a positive clear result in order to make desitions. Usually their’re chemists lab operators. This kind of professional with experience in lignin detection and pH mearurement will be not hard to find in universities or labs, so you shouldn’t have any problem finding one.

    pH measurement and acidic content is something not hard but complex to understand and we as humans always try to simplify it too much. The fact that manufacturers and simple pH meters are not really regulated makes things harder. Its always worth to demand a professional liquid pH measurement of the materials we are about to use instead to trust the seller or the cheap surface pH meter due to the facts Ron Kley previously exposed.


    Yeah, the term acid-free is essentially meaningless. Recycled products are (almost) never long-term archival quality. Always purchase through a reputable vendor that had a good reputation for working with cultural heritage institutions. You are looking for material like mentioned above and with a pH range that is 7.0-9.0, roughly. lignin-free and PAT tested (photographic activity test, but by no means are these materials just for photos- they have just been tested for refined non-reactive qualities) are better indications. Sorry office supply big box, you may be cheap-o, but you don’t have what we need.

    Profile photo of Randi Smith
    Randi Smith

    As I recall, the instructions we received with an acid testing pen said that there could be a delayed reading for certain papers- coated, or slick, or heavy I think. ¬†So I’d think your pen was just slow to get to the correct color. ¬†You could do some test marks on papers around the office to see what you think about response time, but you probably may need better folders.

    Profile photo of Marybeth Tomka
    Marybeth Tomka

    I have been using acid testing pens for many years now and have seen the results go from  purple immediately to not even visible because  the paper is so acidic, and others where the purple slowly fades to yellow and then brand new right out of the wrapper stays bright purple.  As someone on this thread stated, it depends on the acidity of the paper, is is truly neutral, is it buffered, or is your own skin contact increasing the acidity.

    Final comment, I saw no mention of lignen testing pens.  I have a lone, should I not believe the reults?



    Profile photo of Iona McCraith
    Iona McCraith

    I have a groundwood ¬†test pen purchased from Carr McLean (Canadian distributor for museum, archival and conservation supplies) ¬†www.carrmclean.ca ¬†that has proven reliable as a general indicator of the presence or absence of groundwood pulp content in paper. ¬†I also use the Abbey pH indicator pens and sometimes I have found if I have tested a number of acidic papers I sometimes get a false reading on an non-acidic paper. ¬†My assumption is that the felt tip nib has picked up traces of acidity from the acidic papers and needs to be “wiped off” periodically to remove contamination

    Profile photo of Marybeth Tomka
    Marybeth Tomka


    Very good point about wiping off the felt tip!  Would you say the Carr-McLean tip is testing acidity and lignen?




    Profile photo of Iona McCraith
    Iona McCraith

    Hi Marybeth,  Carr McLean sells two different pens with different chemical solution.  The Abbey pen is for testing pH and contains chlorophenol red in the felt tip.  The groundwood test pen contains a corrosive/toxic acid Рhydrochloric acid (muriatic) but works the same way in that a line drawn on paper sample to be tested changes colour in presence of groundwood pulp.

    Profile photo of Paul Hagan
    Paul Hagan

    Hello Marybeth,

    New to this discussion group, but this may be of help.

    We have been looking at a test for detecting materials of Forensic interest. The tests were to be printed on paper strips.

    A proposed test which contained Ferric chloride was initially rejected as it was incredibly sensitive to lignin containing papers. Cotton linter papers (lignin free) show no reaction to the ferric chloride formulation.

    We are looking at ways of quantifying this test, but it seems that even traces of lignin will produce a colour change.

    As a colour test it is valuable to compare the paper to be tested against a cotton linter or lignin free paper (Such as a Whatman Filter). Familiarity with the colour change will not require this comparison on a routine basis.

    This test will discolour the paper so may be regarded as destructive (but only 1mm diameter spot is required for detection) . If you are interested we can furnish you with details. We are working through papers with varying lignin concentrations to establish detection limits for lignin. But suffice to say that the test is extremely sensitive.

    We can supply details (pre-publication) which would let you try it out.

    Materials are all very inexpensive and more crucially safe.

    Best Regards

    Paul & Dymhna


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