Brass clips in conservation: do they protect or damage works on paper?

Rust stains left by steel paperclips and staples are among the most frequent and visible types of damage in graphic art and archival documents. Brass paperclips are offered as a "non-rusting" alternative, but it is important to clarify what they truly solve, under what conditions, and with what limitations.

This article reviews the available evidence on the use of brass paperclips in the conservation of graphic art, archival documents, photographs, and parchment: their documented uses, when they protect the work and when they can damage it, and how they compare to steel, stainless steel, and plastic clips. It draws on industry guidelines and reference studies—Library of Congress, NEDCC, Book & Paper Group of the AIC, Smithsonian Archives—and distinguishes in each point what the evidence supports from what it does not.

Scope: graphic art on paper, archival documents, photographs, and parchment/vellum. Audience: conservator-restorers, archive technicians, and bookbinders.

Technical guide prepared and reviewed by the Innovart conservation team. All statements are supported by the sources cited at the end of the article.

The origin of the damage: iron, not the clip

The stain damage does not come from the clip as an object, but from the iron in its alloy.

A steel or galvanized steel clip, in contact with paper and some ambient humidity, will corrode. The products of this corrosion—iron oxide—migrate into the cellulose fibers and leave a permanent dark discoloration at the point of contact. The National Park Service documents this with an unequivocal photograph: the stain that remains after removing an already corroded clip (NPS, Conserve O Gram 19/5).

The Smithsonian Archives describe the same mechanism: when galvanized steel staples and clips are exposed to indirect humidity—high relative humidity, a basement, an unairconditioned summer—corrosion products form that "can transfer to other surfaces" (Smithsonian Institution Archives). The West Virginia University Libraries summarize it bluntly: metal clips "frequently degrade archival documents," especially in areas without climate control (WVU Libraries).

The decisive point is this:

The reddish rust stain is an iron phenomenon, and brass contains no iron.

Brass is an alloy of copper and zinc. Since it contains no iron, it does not form iron oxide and cannot produce that characteristic orange-brown stain. This is the central—and verifiable—argument in favor of brass: a matter of metallurgical composition.

Why brass clips are used in a conservation workshop

Brass has specific and documented uses as a workshop tool in the conservation of graphic art and parchment:

1. Edge clamping during tension flattening (paper and parchment). When flattening a damp piece, the edges are held while it dries to counteract deformation. It is important to be precise about what the sources say: they describe this technique with bulldog clips, magnets, or weights—not specifically with brass clips— (conservator Rita Udina, ritaudina.com; and the parchment standard of the Book & Paper Group of the AIC, Conservation Wiki). When the edge is held with a metal clip, brass offers the advantage of not leaving the rust stain typical of steel.

2. Temporary securing of sheets during treatment. Keeping document sheets together during intervention, without piercing or stapling.

3. Fixing Japanese paper in mends and reinforcements. Holding Japanese paper in place while it adheres, for tear repairs and edge reinforcements.

4. Provisional assembly in binding and archival work. Securing signatures and documents during processing.

In all these cases, there is a common feature: brass works as a temporary tool, not as a permanent storage fastener. This distinction is crucial and is revisited in the conclusion.

When brass does NOT damage the work

This is what the evidence allows us to state with confidence:

• It does not leave rust stains. As it contains no iron, it completely eliminates the most frequent and visible type of fastening damage in works on paper. Replacing steel with brass completely removes this risk.
• Distributes pressure uniformly. A flat solid brass clip distributes force over a larger surface area than a wire clip, resulting in less mechanical imprint (provided it is not over-tightened).
• It does not break or become brittle over time with normal use, unlike plastic clips that age and wire clips that fatigue (repeated bending does harden brass—see workshop protocol).
• For temporary securing and with controlled humidity, it is the safest metal option compared to steel.

When brass CAN cause damage

Brass prevents iron corrosion, but it is not an innocuous material in all situations. The evidence documents three avenues of damage that must be considered:

1. Mechanical marks do not depend on the metal. Any clip—including brass, plastic, or plastic-coated—can leave an imprint, distortion, or crease, and create a weak point that promotes tearing, especially in thin or brittle paper. The NEDCC is explicit: even plastic or coated metal clips, "though they do not stain paper, do cause distortion and are not recommended" (NEDCC, Leaflet 7.8). The fact that a clip does not stain does not mean it cannot cause damage.

At this point, our clip works in our favor: being flat (distributes the load over more surface area) and made of malleable brass (allows for manual adjustment of the closing force to the thickness of the work), it marks significantly less than a wire clip or a spring steel clip, which apply fixed and concentrated pressure. The mark depends on the pressure—and here you decide the pressure.

2. Copper requires humidity control, but with actual figures, the risk is small. Copper corrosion indoors is, by default, very slow: it is approximately 1% of what it suffers outdoors, and what truly accelerates it is not humidity alone, but high humidity combined with acetic and formic acid vapors—emitted primarily by wood in archival drawers and cabinets (oak can release up to 7% of its weight in acetic acid vapor in an accelerated 2-year test at 48°C; at actual archival temperatures, much slower). This is the same reason why guidelines recommend replacing untreated wooden furniture with inert materials.

In numbers: in the most severe laboratory scenario studied—concentrated acetic acid and 80-100% RH, 21 continuous days—corrosion reached between 11 and 225 nanometers (one micron is 1,000 nm): a barely perceptible veil of patina, not deterioration of the work. This sustained regime would be needed for years, not days, to be relevant—and outside of untreated wooden furniture, within the usual archival range (30-50% RH), the copper in brass is, in practice, insignificant.

Technical note: the 60-70% RH threshold sometimes cited as critical for copper comes from studies of bronze disease, which requires cuprous chloride already present in the metal—pre-existing archaeological corrosion, not clean, new brass; without this contamination, this mechanism is not activated. The Library of Congress studies the mechanism for soluble copper compounds like verdigris: any copper compound "can, under certain conditions, cause deterioration of paper and parchment" (Library of Congress).

3. For permanent storage: the standard is to remove the fastener, or switch to stainless steel with a barrier. When sheets need to be kept together durably, guidelines (NEDCC, Book & Paper Group of the AIC) recommend a metal that does not rust—they cite stainless steel—and interposing a barrier (neutral paper or polyester) between the clip and the work; the AIC standard for wet parchment only allows stainless steel in contact. It is important to understand why: the decisive criterion is not only to avoid iron, but also the general chemical inertness of the metal—stainless steel does not form iron oxide nor does it pose the catalytic risk of copper mentioned above. Brass solves the first part of that criterion—no iron, no rust—but not the second in all conditions; that is why specialized conservation suppliers (PEL, University Products, Conservation Resources) offer it as an alternative that prevents rust, without replacing stainless steel as the reference for total inertness.

But for permanent archives, there is a simpler alternative than changing materials: removing the fastener. This is the standard recommendation—or, at a minimum, removing those already corroded—unless removing them would damage the document (NEDCC). With a nuance that avoids alarmism: the NPS clarifies that it is not necessary to remove a clip if it is free of rust and the environment is appropriate (NPS)—it is a case-by-case decision, not a prohibition. For workshop use or while the document is in use—temporary and monitored—solid brass is a sensible choice, and also malleable.

Brass vs. steel vs. stainless steel vs. plastic

Material	Leaves rust stain	Mechanical mark	Inherent chemical risk	Use verdict
Steel / galvanized	Yes (iron oxide, permanent)	Yes	Iron corrosion	Worst. Avoid on works on paper
Solid brass	No (no iron)	Yes, but adjustable (flat + malleable: you reduce and adjust pressure to thickness)	Insignificant in archival range (30–50% RH, no untreated wood); requires years of very high RH + acidic vapors to be relevant	Safe and adaptable metal option for workshop, with barrier and controlled environment
Stainless steel	No	Yes, and not adjustable (hard and rigid metal, fixed tension: does not conform to thickness)	Very low	Chemically the most inert; cited in guidelines for permanent storage. Downside: rigid, fixed pressure, not very adaptable to delicate supports
Plastic / plastic-coated	No	Yes (distorts just the same)	Depends on the plastic	Not recommended by NEDCC: does not stain but distorts

Conclusion from the table: there is no "perfect clip". There is the right clip for each task. For workshop use, documents in process, or regular consultation—which is most of the actual use—the flat solid brass clip is a sensible choice and far superior to steel. For when a document is placed in permanent storage without further manipulation, the simplest step is to remove the clip—there is no need to change material for that.

How to use a brass clip correctly (workshop protocol)

Used as a temporary tool and following these guidelines, the risk is minimal:

1. Always interpose a barrier. A strip of neutral paper or polyester (Melinex) between the clip and the work. If something is going to mark or migrate, it will do so on the disposable barrier and not on the piece. Important nuance on buffering: use buffered paper (with an alkaline reserve) only for cellulose paper; for parchment (protein base, collagen) and photography (gelatin and processes like cyanotype or albumen), use NON-buffered neutral paper or inert polyester, because the alkaline reserve can damage these materials. This is the method recommended by conservation literature.
2. Do not apply excessive pressure. Mechanical marks come from pressure, not from the metal. A well-placed flat clip holds without digging in. Additionally, since brass is malleable, you can manually adjust the closing force and adapt it to the thickness of the work: the pressure is adjusted, not fixed from the factory (without overdoing repeated bending, which hardens the metal).
3. Reposition periodically. When tensioning and drying, moving the clips every few minutes prevents permanent moisture marks (practice documented by the Book & Paper Group of the AIC).
4. Control humidity. The scenario in which the copper in brass becomes concerning is sustained high RH; in a workshop with a controlled environment, this risk is neutralized.
5. Do not keep it as a permanent fastener. Brass is a working tool, not a long-term storage system. For permanent storage, remove the fastener or replace it with stainless steel with a barrier.

Sources and industry references

The content is based on the following independently verifiable sources:

• NEDCC — Northeast Document Conservation Center. Leaflet 7.8: Removal of Damaging Fasteners. The reference document on fasteners: removal, barrier, and replacement with stainless steel.
• AIC — Book & Paper Group. BPG Parchment Conservation Treatment. Use of clips in parchment tensioning; only stainless steel in contact with damp skin.
• Library of Congress. Project Verdigris. Mechanism of paper and parchment degradation by copper compounds.
• National Park Service. Conserve O Gram 19/5. Criteria for removing (or not) metal fasteners.
• National Archives (NARA). Holdings Maintenance — Paper.
• Smithsonian Institution Archives. Inappropriate Attachments. Physical vs. chemical damage from fasteners.
• Rita Udina — paper and parchment conservator (Spain). Flattened under tension (ritaudina.com). Technique for flattening paper and parchment with bulldog clips, magnets, and weights. Spanish reference in the field.
• Balduqueando — Spanish archival blog. Staples, clips, rubber bands and other adversaries of document preservation.

Conclusion

Brass eliminates the most frequent fastening damage in works on paper—rust stains from steel—and is a documented tool for workshop use, parchment tensioning, Japanese paper fastening, and holding documents in process or active consultation: most of a professional's real-world use. It is not an innocuous material in abstract: like any fastener, it leaves a mechanical mark if excessive pressure is applied (though less than a wire clip, being flat and malleable), and copper requires specific conditions—sustained high RH and acidic wood vapors—that a normal workshop or archive usually doesn't have.

Summary: Brass prevents iron corrosion and is a reliable metal fastener while the document is in use. When it goes into permanent storage without further handling, simply remove the clip.

Innovart's Brass Clip

Our Flat Brass Clips are made of solid brass, with a flat profile—which distributes pressure most uniformly and leaves fewer marks—designed for real workshop use: temporary fastening of documents, prints, drawings, and photographs; fastening Japanese paper in mends and reinforcements; and provisional mounting in bookbinding and archiving.

• Pack of 6 units: L (5 × 2.5 cm) — €13.99 · M (5 × 1.5 cm) — €11.99
• Solid brass, no iron: does not leave rust stains
• Malleable pressure: being solid brass (a malleable metal), you can bend the upper flap to reduce and adjust the closing force to the exact thickness of the item. Brass retains this adjustment—it doesn't return to its initial tension like a spring steel clip—so the fastener molds to thin paper, documents, or delicate supports, and leaves fewer marks.

These are not generic stationery clips: they are solid, not plated—the difference matters because a cheap clip is usually steel with a brass coating, and as soon as the plating scratches or wears off, the steel underneath will rust. Being solid, the material is the same throughout its cross-section: there is no plating that can break and expose a different metal.

→ View Flat Brass Clips in the store

Do you work in a workshop, museum, or institution? For professional orders, bulk quantities, or to inquire about material selection for fastening and conservation of graphic works, write to us at info@innovart.art, via WhatsApp at +34 614 504 565, or from the contact page. Technical advice without obligation.

Frequently Asked Questions

Do brass clips stain paper? They do not leave the typical reddish rust stain of steel because brass does not contain iron. They can leave a mechanical mark if squeezed excessively, just like any clip. With a barrier of neutral paper or polyester between the clip and the artwork, the risk is minimal.

Is brass better than stainless steel for conservation? Both prevent rust stains. Institutional guidelines (NEDCC, AIC) cite stainless steel as a reference fastening material and as the only metal allowed in contact with wet parchment. Brass is an excellent option for temporary workshop use and completely prevents rust; for permanent storage, the standard is to remove the fastener or use stainless steel with a barrier.

Can I leave a brass clip permanently on an archival document? While the document is in active use or process—a folder you're consulting, a file being processed—yes, you can keep it: the NPS guideline itself clarifies that there's no need to remove a clip if it's rust-free and the environment is suitable. What changes is when the document goes into permanent storage and will no longer be handled: there, the standard is simple and you can do it yourself in a minute—remove the clip. There's no need to buy another material for that.

Can the copper in brass damage paper? Under normal archival conditions (30-50% RH, no untreated wood furniture), the risk is negligible: indoor copper corrosion is only 1% of what it suffers outdoors, and what really accelerates it is not humidity alone, but humidity combined with acidic vapors—typically from wood. Even in the most severe laboratory scenario (concentrated acid vapor + 80-100% RH for 21 consecutive days), the corrosion layer barely reaches hundreds of nanometers: a veil of patina, not visible damage. Such sustained exposure would be needed for years, not days, for it to be relevant. In brief workshop use and a controlled environment, this risk does not materialize.

Are they suitable for parchment? Yes, it's a classic use: clips are used to tension parchment during drying and flattening. For parchment, humidity control and a barrier are especially important; and this barrier must be neutral, not buffered, because parchment is protein-based and alkaline reserve can be detrimental to it.

What about photography? With caution. Photographic emulsion is sensitive; always use a barrier, no squeezing, and temporary fastening. The barrier should be neutral unbuffered or inert polyester (avoid paper with alkaline reserve, unsuitable for many photographic processes). For photographic storage, also follow specific photographic material conservation guidelines.

Bibliography

• NEDCC — Preservation Leaflet 7.8: Removal of Damaging Fasteners from Historic Documents. https://www.nedcc.org/free-resources/preservation-leaflets/7.-conservation-procedures/7.8-removal-of-damaging-fasteners-from-historic-documents
• NEDCC — Preservation 101, Session 4: Handling Paper Collections. https://www.nedcc.org/preservation101/session-4/4handling-paper-collections
• AIC — Book & Paper Group Wiki, BPG Parchment Conservation Treatment. https://conservation-wiki.com/wiki/BPG_Parchment_Conservation_Treatment
• Library of Congress — Corrosive Media: Verdigris. https://www.loc.gov/preservation/scientists/projects/verdigris.html
• National Park Service — Conserve O Gram 19/5. https://www.nps.gov/articles/000/conserve-o-gram-19-5-considerations-for-the-removal-of-fasteners-from-archival-documents.htm
• National Archives (NARA) — Holdings Maintenance: Paper. https://www.archives.gov/preservation/holdings-maintenance/paper
• Smithsonian Institution Archives — Inappropriate Attachments: When Good Intentions Go Bad. https://siarchives.si.edu/blog/inappropriate-attachments-when-good-intentions-go-bad-gallery-horrors-part-ii
• Rita Udina — Flattened under tension / Conservación y almacenaje de obra en papel. https://www.ritaudina.com
• WVU Libraries — Metal, Moisture and Memories. https://news.lib.wvu.edu/2020/09/14/metal-moisture-and-memories-how-paper-clips-can-ruin-family-papers/
• Balduqueando — Grapas, clips, gomas elásticas y otros adversarios de la preservación documental. https://balduqueando2punto0.com/2012/04/30/grapas-clips-gomas-elasticas-y-otros-adversarios-de-la-preservacion-documental/
• Canadian Metallurgical Quarterly — Effect of Relative Humidity on Copper Corrosion by Acetic and Formic Acid Vapours. https://www.tandfonline.com/doi/abs/10.1179/cmq.2002.41.3.327
• Strathprints (University of Strathclyde) — Acetic and formic acids emitted from wood samples and their effect on selected materials in museum environments. https://pureportal.strath.ac.uk/files-asset/536741/strathprints027572.pdf
• MDPI Heritage — New Evidence of the Relationship Between Oxidative Hydrolysis of CuCl "Bronze Disease" and Relative Humidity (RH). https://www.mdpi.com/2571-9408/8/9/350