Many inventions happen not by design but through failure. They don’t happen through the failure directly, but because someone was paying attention and remembered the how and why of the failure, and learns from this. One of these inventions is Super Glue, the adhesive that every tinkerer and engineer has to hand to stick pretty much anything to anything, quickly. Although it was a complete failure for the original uses it was developed for, a chemist with good memory and an eye for a helpful product created it in a process he described as “one day of synchronicity and ten years of hard work.”
Super Glue was initially invented in 1942, when the chemist Harry Coover was working on a team trying to develop a clear plastic gun sight that would be cheaper than the metal ones already in use. The team cast a wide net, trying a range of new materials. Coover was testing a class of chemicals called cyanoacrylates. They had some promise, but they had one problem: they stuck to pretty much everything. Every time that Coover tried to use the material to cast a gun sight, it stuck to the container and was really hard to remove.
When the samples he tried came into contact with water, even water vapor in the air, they immediately formed an incredibly resilient bond with most materials. That made them lousy manufacturing materials, so he put the cyanoacrylates aside when the contract was canceled. His employer B. F. Goodrich, patented the process of making cyanoacrylates in 1947, but didn’t note any particular uses for the materials: they were simply a curiosity.
It wasn’t until 1951 when Coover, now at Eastman Kodak, remembered the sticky properties of cyanoacrylates. He and his colleague Fred Joyner were working on making heat-resistant canopies for the new generation of jet fighters, and they considered using these sticky chemicals as adhesives in the manufacturing process. According to Coover, he told Joyner about the materials and asked him to measure the refractive index to see if they might be suitable for use. He warned him to be careful, as the material would probably stick in the refractometer and damage it. Joyner tested the material and found it wasn’t suitable for a canopy but then went around the lab using it to stick things together. The two realized it could make an excellent adhesive for home and engineering use.
So, they patented the use of cyanoacrylate as an adhesive, a patent granted in 1954. Eastman Kodak started selling it as Eastman 910 in 1958, and that exact formula is still sold today. On one memorable demonstration, Dr. Coover lifted the 150-lb host of the TV show I’ve Got a Secret with a single drop of the glue., and lifted a Corvette using the glue.
Dr Harry Coover was awarded the national medal for Technology and Innovation in 2010, but he never made that much money out of Super Glue because the product didn’t catch on until the patent expired and others started making their own versions. That wasn’t the only thing that Dr Coover worked on, though: he is listed on over 350 patents. He always claimed that Super Glue was his favorite and that he was most proud of how the glue was used to save lives in the Vietnam War.
That happened when the US Army realized that you could use it to seal bullet wounds on the battlefield. Because it reacted with the water in the blood, it quickly staunched bleeding and closed a wound until it could be adequately operated on. It forms a thin, strong layer, but it can be fairly easily removed because, as anyone who has Super Glue on their hands knows, once it sets, it has low shear strength. If you get it stuck between your fingertips and it sets, you won’t be able to pull them apart. You can, however, remove it by either waiting until a layer of sweat forms under the glue, or by moving your fingertips back and forth against each other, shearing the bond between glue and finger. Combine this with the fact that cyanoacrylate is not poisonous, and you have a great way to seal a wound quickly.
Modern Super Glues
Modern cyanoacrylate glues come in a wide variety of types, including ones that mix cyanoacryaltes with epoxy to make a stronger bond, and ones that add materials to improve the bonding on porous surfaces. There are also chemicals you can add, making it set quicker if you need to fix something quickly.
How Super Glue Glues
The chemistry of Super Glue is fascinating. Although the specific chemicals used in brands and types differ, all of them are cyanoacrylates, composed of very short chains (called monomers) of carbon atoms surrounded by oxygen and nitrogen and tipped with hydrogen atoms. The chain is relatively stable, but things start to happen as soon as you introduce water.
Water is composed of two hydrogen atoms linked to a single oxygen atom. Still, the bonds that hold these together sometimes fray, leaving hydroxide ions, consisting of an oxygen atom with only one hydrogen atom attached. These float around, looking for something to bond to. When one of these bumps into a cyanoacrylate molecule, it latches onto one of the carbon atoms, but this leaves the carbon atom with a spare electron, where it wants to bond with something. Carbon loves to bond to other carbon atoms, so two of these unbonded cyanoacrylate molecules bond together. This process releases more ions that start bumping into more water molecules, creating more hydroxide ions, and so on. So, once started, the process repeats, creating a long chain of these molecules, a polymer. That is called chain growth polymerization, and it requires very little water to happen. That’s why if you leave the cap off a container of Super Glue, it sets because the moisture in the air sets off the polymerization process.
Water is not the only thing that Super Glue will react with: it also bonds with the oils and proteins in fingerprints. That’s why it can be used to find fingerprints: if you heat it to make a vapor, some will stick to the oil and protein in a fingerprint, which will polymerize more, creating a visible fingerprint impression. This also explains perhaps the most common application of cyanoacrylates: gluing your fingers either together or to the project at hand.
So think about this the next time you reach for a tube of Super Glue to fix a project: this is available because an observant chemist remembered his failures and realized they were not failures; they had just not found the correct use yet.
Featured image: “Super Glue” by Andrew Gustar
Since I started storing my CA glue in a tightly screwed marmelade jar where the bottom is filled with desiccant I didn’t need to buy a new bottle since 2019. Moisture kills CA glue. It’S the absolut best way to store your CA.
Forget putting it in the fridge, it’s too humid there.
That’s a good idea! Probably works well for one-part silicones, too.
You should be paid for this information!
Freezer works great, keeps CA good for years, doesn’t really change viscosity either – ready to use that cold. That said rarely going to actually have a bottle last that long once opened, plus I tend to leave one open bottle out anyway – it will get thicker over time, but that is a good thing really – only have to buy thin stuff and will still have a thicker one around for those times you don’t want the glue running everywhere.
A previous employer had a walk in fridge just for glue. Thousands and thousands of bottles. CA, thread locker in different versions, specialty glues, etc.
There’s no way I can keep a bottle for that long though. The biggest bottles I can easily find here are 20 gram bottles which usually lasts me 2-3 weeks at home. I usually buy 5 bottles when I go to the store so I have some extra. I use a hardware store brand. At work we have Loctite 401 which I find to be horrible. I’d rather use the cheap hardware store brand.
Ywah generic brand for most situations for me, but I do use Starbond stuff for some things. Their water thin and extra thick are the two most useful I’ve found. The thin stuff really flows well and creeps into the tiniest gaps to fill them. Extra thick for things with big gaps like side wall of 3D prints with high layer thickness.
Unopened CA glue stores well in the fridge. Once opened if you put it in the fridge any moisture in the air that’s gotten in will condense and cause the glue to harden. Your tactic of storing the bottle in a jar with dessicant is a good one for opened glue tubes/bottles.
You’re right! I meant open bottles but didn’t mention it, doh!
Anyway, there’s 20 and 50ml bottles now (at least here in DE) which you don’t have to cut the sealed dosing tip off. So they’re kind of “open” from the moment they are manufactured.
I guess completely closed bottles last equally long regardless of how you store them…
However, I find the desiccant method way more workable (than freezer/fridge) because I can put it on/into my workbench that way…
I haven’t used it, but Starbond recommends storing their product in the fridge once opened and guarantees it for 30 months of shelf life. Never was a big fan of CA glue because I usually end up using it for one or two projects then having to throw out a hardened tube the next time I need it. Since getting more seriously into woodworking lately though, its prevalence among the Youtube Woodfluencer set has been impossible to miss, so I’ve been giving it another shake with the fridge tip which seems to be working so far. Maybe Starbond’s warranty is more marketing than fact but I have to imagine they concluded the benefits of the low temperature outweigh the negatives of higher humidity. In any case, I think I’ll try the jar method once I find some desiccant since it would certainly be more useful to have it on hand in the shop.
not sure what is going on but i’ve taken to using super glue with baking soda. just pour super glue into your void, and then tamp down baking soda on top of it. repeat as necessary to fill it out. then file or sand if you want. it sets almost immediately and it fills space and makes a hard plasticy surface.
i’m not really sure how great it is but in my life it has replaced epoxy. it’s a big fad on youtube but i first learned about it because it was recommended as a way to rebuild a nut or solid bridge on a guitar, if the action is too low from wear or defect. you can just fill in the notch completely, and then file a new notch. it’s strong enough to survive the tension and hard enough to transmit the sound, i guess. and most importantly, it’s not too messy to work with, you don’t need to make a mold or leave it be for hours.
I was looking at flooring recently and apparently Stone Plastic Composite is a new trend. Calcium carbonate mixed with some polymer (PVC?) makes a hard base for the planks. I suppose sodium bicarb plus superglue isn’t that different in some ways.
one thing nobody says about using baking soda is the reaction is extremely exothermic. its like burning yourself with hot glue.
Good to know. (Especially in advance)
If you put super glue on cotton it’ll get hot enough to spontaneously combust within a couple of minutes. Pretty useful but also slightly dangerous if you spill some.
Interesting, I’ve only heard of the engineered stone “quartz” countertops, basically the same idea with a harder stone and polyester resin instead of PVC. Seems a bit silly to make flooring out of stone and pretend it’s wood but there’s no accounting for taste. The core material does look pretty drab I suppose from the photos I’m finding but I wonder if they could do the same as the countertops and paint a texture on top with the resin…
My brother would use very fine saw dust from the Balsa wood he would have left over and fill any voids in his r/c model airplanes. Just like your baking soda, it worked like a charm
Curious, I would think the desiccant property of baking soda would inhibit curing.
Reminds me of this research going on at Boise State University: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10032590/
Basically, they’re using ethyl cyanoacrylates as the basis for new polymers and copolymers that are truly recyclable, as the monomers can be recovered and fully re-used via vacuum distillation, much like in one of the recovery steps in the production of new super-glue.
I met one of the authors when she was doing a presentation on the research, and she was very excited to be continuing Coover’s work and finding ways that the original intended uses of these polymers could be realized.
>Joyner tested the material and found it wasn’t suitable for a canopy but then went around the lab using it to stick things together.
lol imagine being out sick that day, coming in the next. “…why is my screwdriver on the ceiling?”
Almost the same effect can achieved with cotton threads as with baking soda. In this way you can make some sort of fiber reinforced bounding. Just alvays use cellulose based fibers not synthetic ones, because it could be nylone or polyethylene not reacting with CA glue. (The material of the glue bottles.)
Be careful using cottonballs, the curing process is exothermic enought to burn, even fire!
I can confirm this. A friend cut a hole in his cotton t-shirt. He repaired it using superglue. It started to smoke and it got very hot and he had to remove his shirt.
My father was a Chief Engineer for the gov’t for 35 years. One of his favorite tales is when a chemical co. sales rep brought him a free sample of this not-yet-released ‘super glue’. It was gonna sell for like $300 for a very tiny bottle. Dad took a lightbulb and a sheet of aluminum, amongst the most difficult things to glue together. He carefully cleaned the bulb and the plate, slathered on a bunch of glue, and clamped it in place. Came back an hour later and lifted the bulb and it broke (from the weight of the attached plate). “Hmmm, the bulb must have already been cracked” he thought and tried again. This time he was less diligent about the cleaning and instead of a clamp he just laid the weight of a book on the bulb. Came back 20 minutes later, lifted the bulb, and it broke. One more time, no cleaning, no weight, waited 5 minutes. Same result! He called one of his secretaries over and had her stick out her finger. He put a drop of glue on it and told her to hold her thumb tightly against it and count to 10. She did, and could not get her fingers apart! Dad just laughed and grabbed some Ethyl-Methyl-Ketone, one of his favorite solvents. It failed to separate her fingers. He spent the next 2 hours trying all sorts of solvents with no luck. Finally had to pry her fingers apart removing several layers of skin. She was so mad she wouldn’t talk to him for a month!
Disclaimer: Dad sometimes embellished his stories a bit, but the jist of them was always true.
Too bad he didn’t think to try acetone, the universal super-glue solvent.
It was in the late 90’s and I was selling a remote control nitro boat to a friend of mine. He wanted to run it before buying it and we headed to the nearest lake and tossed the boat in. We quickly realized that the trim on the motor was all wrong and it needed to be shimmed to raise the motor some. He pulled out some balsa wood and went to cutting a wedge to put behind the motor. He cut his thumb with the razor knife and grabbed the superglue and fixed the cut. I stood there with my mouth agape and declared he needed stitches. He laughed and said he hadn’t had stitches in years because of how good superglue was. The next time I got cut I used the superglue and it works GREAT!!!!!!! Plus I will second keeping a bottle of glue in a jar with dessicant, it lasts forever. I got that tip from a video on the video site.
I once bought a liquid plaster and it smelled exactly like super glue. It just hurts so much when applied that I didn’t want to use it.
Hospitals have been using superglue (aka Dermabond) for years for wound closure, plastic surgeons love it because it will not cause scars to form unlike stiches (the incision may scar but there will not be extras scars from stiches)
I got the tip of my ear snipped during a haircut — not through, but a good flap.
(Bled disproportionately to the amount of pain and the size of the cut! In a shi-shi salon, where all the white towels in the world couldn’t cover it up…)
Went to the doc, and super glue fixed it within minutes. Awesome. For clean cuts, can 100% recommend.
I’ve been using superglue for years on myself. I’m very clumsy. I do a lot of grinding and welding etc, and small cuts are just part of the fun I guess. With small cuts I disinfect them, then use superglue. I wouldn’t recommend anyone else doing that though, but it works for me. It’s probably a better idea to just use a bit of honey and a band-aid on a small wound and anything that requires more than a band-aid should always be checked out by a doctor.
The incision for my thyroidectomy was closed using super glue. A friend who years earlier had a thyroidectomy where the would was closed with stiches was amazed. She wasn’t permitted to bend over or squat down after surgery and had blood seeping from the incision. I had none of those problems.
When I worked in an industrial health clinic we used to Dermabond all the time. As long as you line the edges of the cut up and they aren’t ragged, it does a great job of minimizing scars. And because I have a twisted sense of humor, after standing holding the cut closed for several seconds I usually said something like, “Oh crap!! I think my fingers are glued to your head, we might be stuck together for a while. Do you have a wife? Is she the jealous type?”
I buy the tiny tubes from the dollar store. I get 8 or 10 in a pack. If one dries up I discard it and open a new one.
Be aware that often, one or even a few of those tubes may be empty. Caveat emptor, but still a bargain at $1.50 for a pack of ten. And the CA in those packs often is the *really* thin stuff. Soaks into porous material quickly and tend to run down the job and onto the fingers… Still, I keep a few tubes handy.
We keep a few tubes of superglue in our medicine drawer. They are indispensable for cuts and minor gouges.
Super glue were the bane of school janitor. Someone kept gluing the door lock, forcing my school to cancel a few times. The person responsible was finally caught and his parents had to pay several thousand dollars (1990s dollar) for replacing all the damaged locks a few times over and making new copies of replacement keys.
No one has seen this kid since then.
PS don’t even think of doing this today as a prank or anything. Camera is far more common today than in 1990s and you will be caught soon.
Jeez, in the ’80s all we did was superglue a quarter to the floor of the school foyer to see who’d try to pick it up.
Now my dad (or to hear him tell it, just his friends, never him) in college would synthesize nitrogen tri-iodide, suspend it in alcohol, and squirt it into the door lock of the most hated chemistry professor. Insert key, lock goes boom. Dude was (allegedly) shell-shocked to the point he’d have the janitor unlock his office door. They’d also squirt small amounts on the floor to make the janitor’s broom explode.
Allegedly.
Trade name for super glue for skin is DermaBond. It comes in a neat little pen applicator with a glass crack vial sort of like a glow stick. Many surgeons use it to close skin after surgery so that the scar is minimal. Of course there are usually at least a couple of layers below skin sutured together but the dermis doesn’t get holes in it and this doesn’t scar as much.
They come sterile but occasionally they get opened but not used. They are still perfectly good so I have a few laying around. I’m sure they are crazy expensive but it’s better than not throwing them out.
.
Oh yeah, and it is indeed exothermic as it cures up. Hot as hell actually. Usually surgical patients are asleep but the couple of times I used it in myself -yikes. But better than stitches.
They also sell (or at least sold) something similar as liquid plaster in pharmacies. It was in a small spraycan, smelled exactly like super glue and hurt like hell when applied.
I’m certainly using it wrong, but I can honestly say I have never been happy with a super glued bond.
This.
Other people: Engine falls out of truck. Super glue it back in, drive off.
Me: Super glue broken thingy together. Broken thingy stays broken, has super glue fingerprints all over it. Fingers do not stick together, do not stay stuck to object.
I’ve come to realize that pottery has internal stresses that when it breaks sometimes the pieces will no longer fit together.
Keeping pressure on the joint for an adequate amount of time makes a big difference when glueing some plastics. The problem is if the parts are odd shaped and difficult to clamp, it’s tough to maintain that pressure with just your hands.
Maybe try wetting the surfaces
Every glue has proper and improper uses. Combine CA glue with some rope and you create a super strong composite material (I use it to fix broken plastic items). You can also use it to glue balsa wood. Or put it on the side of a rough PCB to make it smooth. Basically it works great on porous materials and not that well on smooth surfaces in my experience. If a material is very porous or you want to fill holes you can use a thicker version of CA. If the bond needs to be shock resistant I would prefer epoxy since that’s more flexible and won’t crack. You can also combine it with other glues by using a few drops of CA to hold the parts in place when the other glue sets.
It does take some experimenting to find where it works best. Any joint that’s subject to flex or oblique force will probably fail.
Most recent win: my stupid cat chews wires, especially the thin ones on headphones and earbuds. On one set, she broke the insulation but the tinsel conductors were still OK. I opened up the gap a bit, put a dab of superglue in there, quickly pushed the insulation edges together… and that repair has been good for a few months now.
If you apply the superglue in the gaps between your cat’s upper and lower teeth, you may solve the chewing problems as well!
B^)
DON’T!!!!
You can also seal the other end of the cat shut to prevent nasty smells.
Tabasco sauce has been shown to be a deterrent for wire chewing. At the suggestion of a friend, I tried it; I only ever had to use it once, and the kitties seemed to show no ill effects.
I use the COTC 1$ Superglue of different sorts to fix the optical lenses and mirrors, especially from the fused silica. Also I use it for temporary fix of optomechanical parts. The advantage is: when you need to unfix, you simply heat the glued area to the temperature about 150C by heat gun or soldering iron, and glue evaporates fully, without ANY visible traces even on the uncoated optical surfaces. (Be careful, cyanoacrylate vapors are quite toxic and lacrimatory – use the ventilation).
There are several cautions: 1) only the clean cyanoacrylates does not leave traces; jelling agents will leave traces. If you plan to remove the glue traceless by heating – previously check this sort of superglue on the unimportant surface. 2) 3M does NOT recommend usage of cyanoacrylates on the common Na glass surfaces: they claim that glass is alkaline enough to make the polymerisation so fast and hot, that the surface will be damaged by breaking of glass flakes, and the final adhesion is unpredictably unreliable. I personally never see this effects (probably, it depends on glass type and coatings) – but let’s be warned.
3) on many polished or epoxy surfaces, adhesion can be unstable – usage of the “activator” helps a lot
4) simple – but be warned: gluing of coated or painted surfaces will rely not only by adhesion of glue to coating – but also on adhesion of the coating to underlining surface (which can be pure…) – so, the glue will be OK, but coating will detach from one part, left glued to another part.
At work, we had to glue PMMA glass to some ABS chassis. Don’t use superglue for this. Superglue is a solvant for PMMA so it’ll stick very well, but 12h later or so, it’ll crack the PMMA glass.
Fun fact: my old flatmate’s mum is the reason that UK superglue bottles have very distinctive ribbed caps. She mistook an old style superglue bottle that had been left in the bedroom for ear drops. Did both ears before she realised. Surgical application of solvents sadly only caused the glue to run in further then resolidify.
At first I thought, “At least she didn’t mistake them for eyedrops.” But now I’m not sure which is worse.
It is my understanding that cyanoacrylates will literally dissolve the eyeball, so wear eye protection when using the stuff, as the little tubes squirt rather easily. People have suffered serious and permanent eye injuries from it.
Clearly that tactic has really worked.
Finding successful use of “failures”; my garage is filled with these. I call them “solutions waiting for a problem”.
China, Thailand, Kampuchea (Cambodia) and a few more IndoChina countries (where I live) have decided to fingerprint visitors at airports. (Click: https://www.comparitech.com/blog/vpn-privacy/biometric-data-study/ & https://en.wikipedia.org/wiki/Countries_applying_biometrics for detailed world lists).
The Echelon mob also share prints.
Personally I object to biometric data collection (HSBC records/analyses all customers contact lines).
In situations where many prints are sampled such as airports, operators tend to be laxx whereas police tend to be fussy.
I use crazy glue to blank my prints (particularly index fingers) – glue on the finger tip whorls (important areas for identification) are easiest areas. Crazy glue is good as it is hard to remove quickly. If asked where you got it from say you make models or jewellery.
Application should be done on fingers of a hand. allowing time for drying before doing the other. Treated areas should not be allowed to touch each other for 20 or so minutes. Waxed paper can be used to prevent touching.
This is the other side of the coin, the intentional one.
The unintentional one can lock you out of fingerprint biometrics for a day.
The properties of this adhesive differ with the bulk of the side chain. Methyl and ethyl ones are fast reacting and hard. Butyl and higher are slower-reacting, and more elastic.
Superglue variants for glass bonding are often of the butyl variant. (Some can be ethyl plus plasticizer, beware and check MSDS.) The faster harder ones tend to introduce stresses into the surface. (Probably what broke the lightbulbs in the story above.) An example of a butyl-CA is Loctite Super Attak Glass Bond.
Tissue adhesives are at least butyl, more often hexyl, usually octyl. The slower reaction results in less heating and lower chance of thermal damage to the tissues when the application is less careful. They are also way less cytotoxic than the short-chain ones; butyl way better than methyl/ethyl, octyl better than butyl.
The cyanoacrylates can also inhibit growth of gram-positive bacteria, even when solidified. Won’t work on E.coli or P.aeruginosa, will keep MRSA in check. The barrier properties also play role; the superior flexibility of the octyl variant is an advantage here.
There was a study comparing commercial grade and medical grade for tissue use, finding no differences, and suggesting the viability of using commercial when in a pinch (aka low-resource setting).
https://www.wemjournal.org/article/S1080-6032(12)00266-9/fulltext
Holding a rosary to fix, my wife was squeezing the crazy glue tube… In seconds I was stuck both hands holding the rosary! Wife laughing her head off imagining me entering the emergency room like that… My old lab had one solvent left in a brown bottle: Nitromethane. Tried it and it worked super fast (Check Wikipedia). Nitromethane is the antidote – releasing agent for cyanoacrylate glues.. Keep some handy! Finally, the instructions on the glue tube should state that you have to squeeze it yourself… In case of trouble, that would leave you with a free hand…
care to elaborate?
Activists stick themselves to main roads in Berlin and elsewhere with super glue, causing massive traffic disruptions, then use the resulting media coverage to make their point about climate change.
Sitting here dropping CA onto a cotton ball. Not getting any heat production, let alone disturbing flames. So, what am I doing wrong kids?
As an interesting cautionary side note, I do know that the exothermic reaction is real. How do I know? Well, I had a fingernail that was damaged and was growing out rough and in layers. I decided to glue it together and figured I could then sand it smooth. In the process, instead of having the patience to let it set by itself, I grabbed my bottle of spray on CA setting liquid. I use it all the time and did not even give it a thought. OH MY was that a bad idea. It gets HOT when it quick sets. And, when it’s on your fingernail, you can’t exactly not touch it. Luckily, it did not last long enough to blister or leave a burn. But, for the few seconds that it was reacting, it was quite painful!
Oh the joys of exotherms…
Printing resin. Got a drop on hand. Not wanting all the mess with wiping it off and spreading over yet larger area of skin, I got the brilliant idea to shine a strong UV LED on it, with intention to cure it in situ and then cleanly peel it off. Got a small blister and an experience.
Lesson learned, the approach works but it is strongly advised to slooowly get closer to the lamp, feeling the resin getting just warm, instead of shining all the power point-blank.
The superglue activators are often polyamines in solvent. Likely could be improvised from the amine component of a common two-part epoxy.
A few years ago we were getting ready to go out to an event in the city, for which we were taking the train.
We didn’t have much time to spare before leaving and I noticed my cheap sandshoe upper had split.
Rather than taking the show off I grabbed a tube of superglue and did a quick repair.
Only problem was, I used too much and glued my fingers to the shoe.
I had to apologise that I didn’t think we would make it but I managed to undercut the shoe layer off with an Exacto, and spent the time on the train trying to pick the vinyl off my hand.
An increasing number of entities are collecting fingerprints. That is full view copies of prints like Cops. One of the latest is THHAILAND. Bio-identity is protected in many countries, although some US Cop outfits are running round with portable fingerprint samplers.
BUT CRAZY GLUE BEATS THEM
An increasing number of entities are collecting fingerprints. That is full view copies of prints like Cops. One of the latest is THHAILAND. Bio-identity is protected in many countries, although some US Cop outfits are running round with portable fingerprint samplers. Both Laos & Cambodia (Kampuchea) copy the USA with info.
I (legally) possess passports from several countries (and have several citizenships) and recently I crossed a border and the bast**ds challenged my identity from an earlier crossing in a Euro country with another countries passport.
BUT CRAZY GLUE BEATS FINGERPRINTING!
Carefully covering your fingers and pal, with CRAZY GLUE defeats these scans and usually (but not the Cops) could care less about the print quality.