Wikipedia:Reference desk/Archives/Science/2019 March 16

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March 16

Coating steel chainmail to protect against corrosion

I live in the butthole of the UK (the UK arguably has more than one butthole) and knife crime is increasing so I was considering buying a stab-resistant shirt/vest that I can wear under normal clothing when forced to venture outside (those last four words are kind of a joke). Slash-resistant clothing is cheaper but slash-resistant does not imply stab resistant and the cheapest options for stab-resistance seem to be either fish-scale-style overlapping steel plates sewn into a vest or chainmail (riveted, not butted). Zinc plated steel chainmail shirts are about double the price of oiled steel. Of course I don't want oil on my clothes so I'd need to wash and plate the steel somehow and I was wondering which would be easier for something as inconveniently shaped as a crumpled-up chainmail shirt. Options seem to include galvanizing, bluing or anodizing (painting, phyisical vapor deposition and powder coating seem less practical). I was hoping that someone might happen to have some insight into which method would be most practical for such an inconvenient piece of steel. Maybe this explains the high cost of the plated versions. If I *knew* I was going to be stabbed then I'd just pay for it and be done but there's a very good chance I won't even see a knife so I'm tempted to go chintzy. 85.210.94.23 (talk) 13:03, 16 March 2019 (UTC)

Buy a stab vest, as worn by nightclub bouncers. They're far cheaper than they used to be.

Chainmail (for practical levels of affordability) isn't stab proof. It's not bad at resisting a sword slash, but it will pierce with a direct stab and a short, strong blade. As most chavs aren't very good knife fighters, and they've now moved away from Stanley knives, stabbing is the most common sort of assault.

Chainmail (the cheap sort) is aluminium and not riveted or welded links. Unriveted links can burst under a strong stabbing thrust. Riveting is more expensive, enough to make it expensive compared to modern polymer body armour.

Also note that in some parts of town, wearing any sort of armour is seen as arrestable. Andy Dingley (talk) 13:25, 16 March 2019 (UTC)

My understanding is that the polymer stuff is only slash resistant as the weave moves apart for stabs? I wouldn't buy aluminium or butted mail, only riveted steel. I also note that the cheaper stab vests which use steel plates don't cover the shoulders or upper arms where some people do get stabbed and also aren't breathable. 85.210.94.23 (talk) 14:54, 16 March 2019 (UTC)

When did it become common to produce chainmail from anything other than iron or steel? And what's the point of it, if it's made of something as light as aluminium? Nyttend (talk) 13:52, 16 March 2019 (UTC)

I think the butted and aluminium variants are for people who want to re-enact or LARP. I'd only buy riveted steel if I go for chainmail over steel plates. 85.210.94.23 (talk) 14:54, 16 March 2019 (UTC)

One possibility if you want to make steel or iron more corrosion resistant is to use the same method used to season cast iron or stamped steel pans.[1][2][3] --Guy Macon (talk) 17:58, 16 March 2019 (UTC)

Context: "It's relatively unusual for a violent incident to involve a knife, and rarer still for someone to need hospital treatment. Most violence is caused by people hitting, kicking, shoving or slapping someone, sometimes during a fight and often when they're drunk; the police figures on violence also include crimes of harassment and stalking. The Crime Survey for England and Wales, which includes offences that aren't reported to police, indicates that overall levels of violence have fallen by about a quarter since 2013". BBC - Ten charts on the rise of knife crime in England and Wales Alansplodge (talk) 20:11, 17 March 2019 (UTC)

^This. The source shows about 4k hospital admissions per year in England following knife attacks (I expect "stabbing" would usually result in a hospital admission), which turns out to less than 0.1 per 1000 people (and I assume the stats are not very different in the rest of the UK). In comparison, road accidents cause 25k "serious injuries" and 170k "casualties of all severity" per year in the UK, or 0.4 and 2.6 per thousand people respectively. Unless you have extremely detailed reasons to expect being stabbed, no matter what UK orifice you are in, you are taking more risks by going 5mph above the speed limit than by not wearing chainmail.

While you are free to wear armor (if local legislation allows it), I would encourage to take such decisions based on a rational risk analysis rather than out of TV-induced fear. Tigraan^{Click here to contact me} 08:59, 18 March 2019 (UTC)

There are currently no laws restricting the purchase or wearing of body armour in the UK. [4] A gentleman may still sally forth wearing a full suit of armour should the fancy take him; we Britons might not have the right to bear arms, but we do have the right to bear armour. Alansplodge (talk) 17:55, 18 March 2019 (UTC)

And to prove the point "PATRIOTIC Colin Bickers will set off on St George’s Day on Saturday to walk 65 miles to the Royal Wedding wearing a five-stone (70 lb / 32 kg) suit of armour". [5] although the sword might be an offensive weapon under the Prevention of Crime Act 1953, Section 1(1), unless he can think of a "reasonable excuse". Alansplodge (talk) 22:08, 18 March 2019 (UTC)

Plate Armor has very often been treated by Bluing (steel). It is still done to weapons (Finisher) and tools today. Regarding Chain Armor i doubt there where any other measures than clean, polish and keep dry. --Kharon (talk) 01:08, 19 March 2019 (UTC)

The OP might want to consider Dyneema, a high performance fabric anti-stab fabric described in Body armor. No worries about metal. Cullen³²⁸ Let's discuss it 01:47, 19 March 2019 (UTC)

I would expect that dipping the chain mail in a melted thermoplastic would work. The plastic would be lightweight and flexible, and protect the metal from water. It wouldn't be breathable, though, so you'd want to have it loose, with cotton or other wicking fabrics underneath. You would need to periodically reapply the plastic coating, as it would tend to loosen over time. SinisterLefty (talk) 02:06, 19 March 2019 (UTC)

Cherenkov radiation

Quoting this article:

While electrodynamics holds that the speed of light in a vacuum is a universal constant (c), the speed at which light propagates in a material may be significantly less than c. For example, the speed of the propagation of light in water is only 0.75c. Matter can be accelerated beyond this speed (although still to less than c) during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than that at which light propagates in the same medium.

Would it be accurate if I changed material to translucent material? Upon reading this paragraph, I initially wondered why Cherenkov radiation doesn't result from fish swimming through muddy water, since light can't penetrate the water-mud-etc mix at all. I'm left guessing that Cherenkov radiation is the result of surpassing the speed of light in materials through which can propagate at some speed. Nyttend (talk) 13:49, 16 March 2019 (UTC)

The speed of light in a material is related to the refractive index of the material, itself related to the material's relative permeability and permittivity. These can be entirely unrelated to the opacity of the material. For instance, the light might be moving through an opaque aqueous material at the same speed it does through a translucent one, but is simply being scattered or absorbed so quickly that no light makes it through more than a thin layer. Someguy1221 (talk) 19:32, 16 March 2019 (UTC)

Cherenkov radiation does not necessary mean visible light. It can be radio, infrared or ultraviolet etc. The term translucent material is meaningless in this context. Ruslik_Zero 19:46, 16 March 2019 (UTC)

Thank you both for the helpful responses; this is why I didn't want to be WP:BOLD. Nyttend (talk) 11:29, 17 March 2019 (UTC)

Several things. 1) Fish can't swim at 0.75c, so the rest of the question doesn't matter, 2) muddy water is only opaque at some (not all) wavelengths, so also a non-starter and 3) the speed of light in "muddy water" would not be significantly different from that in clear water, so also not an issue. The rest of the question, however, is completly pointless until you find a fish that can swim at some insane fraction of the speed of light. The answer to "why Cherenkov radiation doesn't result from fish swimming through muddy water" is "What effing fish are you thinking about?!?" --Jayron32 02:07, 17 March 2019 (UTC)

Even the fish speeding at 0.75c would be outsped by light whose speed in water is 0.7502c according to wolframalpha.com, which seems a tiny difference unless you calculate that a photon outpaces the fish by 37 miles (60 km) per second. DroneB (talk) 11:55, 17 March 2019 (UTC)

I think the OP assumes that speed of light in muddy water =0, so fish are faster than light in this medium. Doroletho (talk) 17:27, 17 March 2019 (UTC)

...which was an incorrect way of seeing things, as Someguy1221 (well) explained. Tigraan^{Click here to contact me} 09:03, 18 March 2019 (UTC)