If you've ever pulled out an old scrapbook or photo album only to find the pages turned brittle, yellowed, and crumbling at the edges, you've seen paper acidity in action. For crafters, scrapbookers, bookbinders, and mixed-media artists, understanding acidity isn't just a technical curiosity — it's the difference between a piece that lasts for decades and one that destroys itself (and anything touching it) within a few years.
This guide breaks down what paper acidity actually is, how to test for it, and what it means for the long-term survival of your art.
What Is Paper Acidity, Really?
Paper acidity refers to the pH level of paper, measured on a scale from 0 (highly acidic) to 14 (highly alkaline/basic), with 7 being neutral. Most modern paper acidity problems trace back to how the paper was made.
Traditional paper was produced from cotton or linen rags, which are naturally low in acid and quite stable over time. But starting in the mid-1800s, papermakers shifted to wood pulp to meet rising demand — and wood pulp contains lignin, a compound that breaks down into acidic byproducts as it ages and is exposed to light and air. To complicate things further, many manufacturers used alum-rosin sizing (a chemical treatment that helps paper hold ink without bleeding) which is itself acidic.
The result: a huge share of paper produced from the 1850s through the late 20th century is acidic by nature, and acidic paper essentially eats itself alive over time through a process called acid hydrolysis, where the cellulose fibers that give paper its strength break down chemically. This is why so many newspapers, paperbacks, and old craft papers turn yellow, brittle, and fragile.
Why Acidity Matters for Archival Art
For artists and crafters, acidity isn't only about the paper itself — it's about everything that paper touches.
Migration is the real danger. Acid doesn't stay put. It migrates from acidic materials into anything they contact — including photographs, other papers, fabric, and adhesives. This is why archivists are obsessive about keeping acidic materials away from items meant to last. A single acidic mat board behind a watercolor painting, or one cheap acidic page in a scrapbook, can slowly degrade everything around it.
It compounds with light and humidity. Acidic paper breaks down faster when exposed to UV light, high humidity, or heat. A piece stored in a sunny room on acidic paper can show visible damage in just a few years, while the same piece on acid-free paper in the same conditions might show none.
It affects color and ink longevity too. As acidic paper degrades, it often yellows or browns, which changes how colors and inks appear over time — even if the medium itself (say, a watercolor or pastel) is stable.
For anyone making cards, scrapbooks, journals, collage work, or mixed-media pieces meant to be kept or passed down, this matters enormously. A gorgeous piece on the wrong paper can quietly destroy itself.
How to Test Paper for Acidity
You don't need a chemistry lab to check whether your paper is acidic. Here are the main methods, from simplest to most precise.
1. pH Testing Pens
This is the most practical option for most crafters. pH testing pens (sometimes sold as "acid detector pens") contain a chlorophenol red indicator solution. You draw a small line on the paper:
- Purple/violet = paper is alkaline or neutral (generally safe, pH 7+)
- Yellow = paper is acidic (pH below ~6.5)
These pens are inexpensive, widely available from archival and bookbinding suppliers, and give a quick visual answer. The drawback is they only tell you whether paper is acidic, not exactly how acidic, and they leave a small mark, so test on a scrap or hidden edge.
2. pH Test Strips
Similar concept to testing pens, but using litmus-style strips. You dampen the strip slightly with distilled water, press it against the paper for a few seconds, and compare the color change to a reference chart. These are a bit more precise than pens for estimating an actual pH number, though still an approximation.
3. Digital pH Meters (Surface Probes)
For more serious accuracy — useful if you're working with valuable or historical materials — surface pH meters use a flat probe with a small water droplet to measure pH electronically. These give a numeric reading rather than a color estimate and are the standard tool in conservation labs. They're more expensive and require calibration, so they're generally only worth it for serious archivists, conservators, or collectors.
4. Look for Manufacturer Labeling
Many craft and art papers now state "acid-free," "archival," "pH neutral," or "buffered" directly on the packaging. This isn't a substitute for testing if you're working with unknown or vintage paper, but for new purchases it's a reliable shortcut — reputable archival brands test their products in-house.
5. Visual and Tactile Clues (Rough Estimate Only)
While not a reliable test on its own, yellowing, a musty smell, and brittleness in older paper are red flags worth following up with an actual pH test.
Acid-Free vs. Archival vs. Buffered: Know the Difference
These terms get used loosely, but they mean different things:
- Acid-free means the paper has a neutral or higher pH at the time of manufacture (generally pH 7 or above). It does not guarantee the paper will stay that way forever, since other factors (light, pollution, humidity) can still cause acid to develop over time.
- Buffered (or alkaline-buffered) paper has an alkaline reserve added — usually calcium carbonate — that actively neutralizes acid as it forms, extending the paper's stable life considerably. This is generally the gold standard for long-term storage.
- Archival quality is a broader marketing term that should mean acid-free, lignin-free, and stable, but isn't strictly regulated, so it's worth verifying with a pH test if the claim matters for your project.
- Lignin-free specifically means the wood pulp's lignin has been removed during processing, which matters because lignin is one of the main sources of acid formation over time, even in paper that starts out acid-free.
For genuinely long-term pieces, look for paper that is acid-free and lignin-free and, ideally, buffered.
Practical Tips for Crafters
- Test before you commit, especially with vintage papers, ephemera, or anything bought secondhand for collage or junk journaling. A quick pen test on scraps tells you whether it's safe to combine with other archival materials.
- Isolate acidic materials if you want to use them anyway (many crafters love the look of aged newspaper or vintage ephemera). Use a barrier — such as an acid-free interleaving sheet, encapsulation in archival sleeves, or a deacidification spray — to slow migration into surrounding pages.
- Use acid-free adhesives too. Many cheap glue sticks and tapes are acidic and will degrade your project from the inside even if the paper itself is fine.
- Store away from light and humidity swings, since both accelerate acid-driven breakdown regardless of the paper's starting pH.
- Consider deacidification sprays (such as those using calcium carbonate or magnesium oxide) for existing acidic pieces you want to preserve — they can raise pH and add a buffering reserve, though they work best as preventive maintenance rather than reversing damage that's already occurred.
Will sealing the paper with an acrylic medium solve the problem?
I have seen advice given on various forums stating that a layer of acrylic medium on the paper will effectively make the paper acid free as it seals the paper. However after researching this I have found that, no — acrylic mediums don't make acidic paper archival, and in some cases they can make things worse.
Why it doesn't work:
Acrylic medium (gloss or matte) is essentially a polymer coating. It seals the surface, but it doesn't change the paper's internal chemistry. The acid causing degradation isn't sitting on the surface — it's baked into the cellulose fibers themselves, either from lignin breaking down or from acidic sizing used in manufacturing. Acrylic medium has no buffering agents (like calcium carbonate) to neutralize that acid, so the chemical process of acid hydrolysis keeps happening underneath the coating, slowly weakening the fibers regardless of what's on top.
Why it can actually make things worse:
- Acrylic film is fairly impermeable. Sealing acidic paper on both sides can trap moisture and acidic byproducts inside the paper rather than letting them dissipate, potentially accelerating breakdown in a sealed micro-environment.
- It can also trap residual solvents or plasticizers from the medium itself against the paper.
- Acrylic mediums aren't all UV-stable or chemically inert over decades — cheaper ones can yellow or become brittle themselves with age, adding a second degradation layer instead of preventing one.
What actually works:
If you want to genuinely stabilize acidic paper, you need a deacidification treatment, not a sealant:
- Deacidification sprays (e.g., those using calcium carbonate or magnesium oxide, like Bookkeeper or Wei T'o) chemically neutralize existing acid and leave an alkaline buffering reserve in the paper.
- Interleaving with acid-free/buffered tissue prevents acid migration to neighboring pages, even if it doesn't fix the acidic sheet itself.
- Working on acid-free or buffered paper from the start is the most reliable long-term fix — there's no surface treatment that substitutes for the paper being stable to begin with.
So: acrylic medium is great for protecting a painted surface from abrasion, moisture, or UV exposure, but it should be thought of as a finish, not a conservation treatment. If archival longevity matters for the piece, it's worth pH-testing the paper first and either deacidifying it or transferring/mounting the work onto archival-grade paper or board.
The Bottom Line
Paper acidity is one of those invisible factors that can quietly undo hours of careful craftsmanship. The good news is that testing for it takes seconds, archival-grade materials are widely available and often not much more expensive, and a few small habits — testing scraps, using acid-free adhesives, and isolating questionable materials — go a long way toward making sure your work survives as long as you intend it to.
Whether you're scrapbooking family photos, building an art journal, or creating mixed-media pieces meant for the long haul, a little attention to pH now can save your work from disappearing later.
I have recently done my own tests with a pH pen on a variety of papers. If you are interested to see my results click here.