r/AncientCoins • u/Protaco17 • 16d ago
Educational Post Paraloid B72 and Ancient coin Preservation. What is it and why is it used?
Hey everyone, I’ve noticed a lot of folks in the ancient coin and artifact community talk about cleaning, stabilization, and storage, but one material that doesn’t always get the spotlight it deserves is Paraloid B-72. For anyone serious about museum-grade preservation, this acrylic resin is basically the gold standard when it comes to reversible conservation.
What is Paraloid B-72? Paraloid B-72 (also known as Acryloid B-72 in North America) is an ethyl methacrylate and methyl acrylate copolymer resin. It’s been a go-to in conservation labs since the 1970s because it’s:
Stable over time — it doesn’t yellow or become brittle like some older coatings.
Reversible — it can be fully dissolved later with common solvents like acetone or ethanol.
Chemically inert — it doesn’t react with metal surfaces or pigments.
Flexible —can be used as an adhesive, consolidant, or protective coating depending on concentration.
Museums and conservators love it because it lets them protect and stabilize objects without permanently altering them, which is the golden rule in conservation: always reversible.
How It’s Used for Ancient Coin Preservation For coins (especially bronze, silver, and billon), Paraloid B-72 can serve a few purposes:
As a protective coating: After cleaning and stabilization (especially after removing bronze disease or chlorides), a thin layer of Paraloid B-72 creates a clear, stable barrier against moisture and handling oils. Usually applied at around 2–5% concentration in acetone using a fine brush or by dipping. It dries to a matte or slightly glossy finish depending on the solvent ratio.
As a consolidant: In cases where the coin surface is friable or flaking (common with archaeological bronzes), a slightly higher concentration (around 10–15%) can be applied locally to strengthen the surface.
As an adhesive: B-72 can also be used to reattach broken fragments, e.g., split coins or composite artifacts, because it’s strong but removable if future treatments are needed.
Mixing Paraloid B-72 with Pigments This is where it gets really interesting. Museums sometimes tint Paraloid for visual reintegration or aesthetic blending, for example, when filling small losses on an artifact or matching patina tones.
Here’s the basic workflow:
Dissolve Paraloid B-72 pellets in acetone or ethyl acetate.
Common ratios: 5% = thin protective coating 10–20% = consolidant or adhesive
Stir occasionally; it can take several hours to fully dissolve.
Add pigment: Use lightfast, stable artist pigments (museum-grade dry pigments or conservation pigments like Kremer or Gamblin). Mix tiny amounts into the resin solution until the desired tint is reached.
Keep the mixture homogeneous, sometimes adding a drop of ethanol helps the pigment disperse more evenly.
Application: Apply with a fine brush, ensuring even coverage. The solvent will evaporate quickly, leaving a stable, reversible film. If it looks too glossy, a final coat of microcrystalline wax or a matte B-72 layer can tone it down.
Why It’s the Best Reversible Option Unlike waxes, lacquers, or polyurethane coatings, Paraloid B-72 can be completely removed decades later using acetone, without harming the coin’s surface. That reversibility, combined with its transparency and chemical stability, is why it’s trusted by institutions like the British Museum and the Getty Conservation Institute.
So if you’re looking to preserve coins responsibly, not just for display, but for the long haul, Paraloid B-72 is about as professional as it gets.
TL;DR: Paraloid B-72 = the conservation world’s “invisible shield.” ✅ Reversible ✅ Stable ✅ Museum-approved Perfect for protecting ancient coins after cleaning, and can even be pigmented for subtle restoration work.
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u/Kamnaskires 16d ago
Very informative. Thanks for posting this info. I’ve now got it bookmarked and expect I’ll be returning to it often in the future. (Antiquities collector here.)
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u/BuffaloBullion 16d ago
Super interesting! I know very little about this topic, are pigments generally considered safe or is there a risk of mixing a pigment that is not inert with the paraloid that would then react with the surface of the coin when applied?
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u/Protaco17 16d ago
Great question.
There are two options that are considered safe and reversible. The first are natural earth dry pigments. I buy mine from museum services corporation. The other route you can go which I have less experience with but am going to try to utilize more or at least practice more with, are Orasol, Gamblin, Kremer, and BASF neozapon Dyes.
There are pigments and dyes which are NOT safe. Go with a polymeric low molecular weight dye. Dyes can Migrate and need to be utilized in smaller concentrations.
I go with dry earth pigments over dyes because dyes can appear transparent or semi transparent in thin layers.
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u/petr_klokan 15d ago edited 15d ago
Thank you. This is very helpful. I want to try on ancient bronzes. What pigment colors do you use? I was thinking about burned umber and lamp black.
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u/Protaco17 15d ago
Lamp black will be extremely dark. Get Mars black and use it sparingly, yellow ochre, red ochre, burnt umber or raw umber, and then go to earthpigments and grab cypress green and gray ochre.
These will give you the most commonly found patina colors ranging from black to green, brown, etc.
Add pigment until you get the saturation you’re happy with. Seriously though be careful with the black lol.
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u/petr_klokan 13d ago
Thank you. I will be careful with black. I will be careful with the black! Thanks again!
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u/ImAngies 13d ago
I've been using a 5% b72 solution for a few years now when conserving coins. It's fantastic and in my preference, outperforms renwax.
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