Passivation of Bird Bands
This article originally appeared in the Fall/Winter 2025 issue of The Watchbird.
Passivation of Stainless Steel Leg Bands by American Bird Bands
Written by Matthew Honig, owner
In this new era of laser-engraving technology being used across the globe for bird leg bands, it’s important to be well-informed of the potential benefits, risks, and pitfalls that come with laser-engraving on stainless steel. This article outlines our journey as a company as we seek to make the best stainless steel bird leg bands in the world. Hopefully, it gives breeders, conservationists, zookeepers, pet store owners and aviculturists new understanding of the complicated world of stainless steel leg band manufacturing.
My name is Matt Honig, and I am the owner of American Bird Bands. For the past four years we have partnered with the AFA to make their leg bands, both aluminum and stainless steel. We started out with a single laser engraver and quickly figured out the necessary settings to engrave deep into both metals. Deep laser engraving works great for aluminum but presents a unique problem for stainless steel. When laser-engraved, the engraving itself becomes susceptible to rust!
To understand this issue, please allow me to briefly explain why stainless steel is rust resistant. Stainless steel differs from other types of steel in that it contains a high level of chromium. The two most common types of stainless steel are 304 and 316. 304 contains 18.5% chromium, while 316 contains 17.5% chromium and 2.2% molybdenum. The addition of molybdenum makes 316 even more rust-resistant than 304. In any case, the chromium in the stainless steel reacts with oxygen in the air to form a thin layer of chromium-oxide, which protects the metal from corrosion. If the surface gets scratched, cut, or sanded, then the chromium-oxide barrier is temporarily removed, but should form automatically again unless something gets in the way.
When stainless steel leg bands are stamped, the chromium-oxide barrier is breached, but should rebuild itself almost immediately. The only reason it may not is if the material used to stamp it was made of iron and left iron particles on the surface. This can be quickly and easily removed using the chemical passivation process that I will describe later. However, when stainless steel is laser-engraved, the metal is literally burned away by the laser, and the result is a layer of burnt iron stuck to the engraving. This burnt iron can and will rust if exposed to water.
Laser experts advised us to do what they called an “annealing mark” on the stainless steel. This involved using low power and slow speed to heat the surface of the metal enough to mark it black, but not enough to burn off the protective layer. If you come across stainless leg bands that feel smooth to the touch, this is likely how it was done. Unfortunately, these marks proved too impermanent for use on leg bands. We returned to deep engraving. At first, we just sanded the burnt material from the surface of the leg band, leaving a clean-looking black engraving with no signs of rust or discoloration. But we discovered that the black color of the engraving was caused by still more burnt iron inside of the letters and numbers! And when exposed to water for long periods, especially when it was only recently engraved, this would rust. And once rust gains a foothold in a piece of stainless, it can be hard to contain. It can spread beyond the engraved letters and over time weaken the integrity of the leg band.
Our goal as a company has always been to make leg bands that are safe, effective, affordable, and long-lasting. Especially when it comes to stainless steel, we want our bands to last for a hundred years. We want the band to always outlive the bird.
We put our energy into two different but related endeavors. First, to find a way to stamp the leg bands. And second, to find a way to make the laser-engraved leg bands rustproof. We accomplished the first objective relatively quickly, though it had its limitations. The bands could be stamped with the aid of a pneumatic machine, but most of the work was still done by the human operator. In addition, only 13mm and larger bands could be stamped. I had a machine shop customize a part for the device that allowed bands as small as 8mm to be stamped, but it proved too fragile for the pressure of the stamping. A slightly larger piece, for 10mm and larger bands, was then customized and has been used ever since.
Rustproofing laser-engraved bands proved much more difficult. We learned that this process of restoring the passive chromium-oxide layer is called passivation and is traditionally done using nitric or citric acid. Citric acid was by far the easier option, as it required no special ventilation or disposal procedures. So, after sanding the stainless bands, we experimented with submerging them in a bath of citric acid for thirty minutes, then rinsing and drying them. In theory, the citric acid would remove the iron particles from the surface of the stainless steel and encourage the rebuilding of the chromium oxide barrier. No residual acid was left on the leg bands afterwards, and the procedure was perfectly safe for medical and food-contact grade items. In our testing, the passivated bands displayed better corrosion resistance than the non-passivated laser-engraved bands, but still not as good as the stamped bands.
We offered both the laser-engraved and stamped stainless steel bands for sale, with the warning that the stamped bands were more rust resistant than the laser-engraved ones. We continued to passivate the laser-engraved bands with the citric acid bath. This continued without issue or complaint until August 2025, when I attended the AFA convention in Raleigh, North Carolina. There, I met a handful of birds with my leg bands. In particular, I observed two macaws with my stainless leg bands. One had a stamped band from 2024 that looked to be in good condition. The other had a laser-engraved 2025 band that was already rusting. This was deeply troubling to me. I made a resolution there and then to solve this problem and increase the rust-resistance of our stainless steel leg bands. When I returned to work in Maryland the following week, I rented an additional two rooms in our building and made them our passivation laboratory.
Ultimately, I made the same decision as before, only more so. To increase our stamping ability, and to increase the rust-resistance of our laser-engraved leg bands. For the former, I bought punching machinery as well as custom dies and molds that would allow us to stamp more bands faster. This should allow us to soon be able to stamp all sizes of split bands. In addition, I decided to make these 316-grade instead of the current 304. I am still making upgrades in this area, and hopefully one day will be able to stamp all the stainless steel leg bands.
In addition, I began experimenting with passivation technology that would significantly increase the corrosion resistance of the laser engraved bands. I discovered that citric acid works best in specialized ultrasonic tanks that use specific frequencies and temperatures to remove iron particles. I also realized that some sort of abrasive action would be required to mechanically remove burnt iron from the inside of the engravings. Without this, the citric acid could not properly perform its job, as there was simply too much caked-on burnt material. For this, we purchased high-powered magnetic tumblers. The leg bands are placed in a bowl with some water, detergent, and thousands of tiny (.2 - .5mm x 5mm), magnetic stainless steel pins. This bowl is then placed on a machine which spins a magnetic disk under the bowl at 3450rpm, causing the pins to spin and impact the tiny crevices in the engravings, loosening and removing the burnt iron. We went through a few of these machines before we found one high-powered enough to accomplish the task. Most of these machines turn off after 30 to 60 minutes, but we needed one that could run for hours at a time.
Finally, we invested in tumbling and polishing machinery that would free us from hand-sanding the leg bands prior to putting them in the magnetic tumbler. An initial run in a tumbler with stainless steel shot removed most of the slag from the laser-engraving process. Running the bands in the tumbler overnight with a citric acid-based detergent solution loosened the burnt iron deep in the engraving, making the magnetic tumbling to follow even more effective.
ASTM A967 sets international standards for stainless steel passivation. It outlines seven acceptable tests that may be used to evaluate passivation and corrosion resistance. The simplest test is to take the passivated item and submerge it in distilled water for one hour, then take it out and let it dry for one hour. This is repeated twelve times for a total of twenty-four hours. The item is then observed and if no rust is visible, the item passes the test and can say to have been properly passivated. It took several months of experimenting but with the combination of magnetic tumbling and ultrasonic passivation we found that we could achieve ASTM A967 standards of passivation consistently by Thanksgiving 2025. In addition, we could visually tell if the bands needed to go back through the process again.
We also developed our own test, simpler but harder to pass. We submerged the bands in a cup of tap water for 24-48 hours. If any rust was visible by the end, the bands failed and were re-passivated.
We now also passivate our stamped bands in citric acid briefly to remove any iron that may have attached itself to the leg band during the stamping process. This makes the stamped leg bands even more corrosion resistant than before, and they are still the best choice in our opinion. And as we gradually upgrade our entire stainless steel inventory to 316, the stamped leg bands should be appropriate for even waterfowl and other marine birds. However, we are now confident that our laser engraved leg bands are passivated correctly, in accordance with international standards.
It is an honor to serve the avicultural community, and we seek to always be in conversation with it. If you have any questions, concerns, or suggestions please reach out to me at bemorebirds@gmail.com.
Fresh from the laser
After polishing, before passivation. Note that the aesthetically-pleasing and easy-to-read black color of the engraving is due to burnt material. Leg bands being used for promotional or artistic purposes can usually be packaged and shipped after this step.
After passivation. Most of the black material has been removed and the leg band is thoroughly rust-resistant.
Counter with magnetic tumbler, dryer, and two ultrasonic cleaners. One of the ultrasonic cleaners is used for citric acid, the other for rinsing. Rinsing with ultrasonics helps ensure that all the citric acid is removed. Underneath, there is a variety of detergents and chemicals.