
Why shaving dulls even the sharpest of razors - WalterSobchak
https://news.mit.edu/2020/why-shaving-dulls-razors-0806
======
nordsieck
1\. I'm not super familiar with razors, but I am pretty familiar with knives.
The chipping they describe is typical of a knife that is ground with an angle
that is too acute. In knives made of hard material they fail by chipping,
whereas in knives with a softer edge (think German kitchen knives) the edge
rolls instead.

The classic solution to this problem is to grind the secondary bevel more
obtusely so that there is more material to "support" the edge. This results in
a knife that is less sharp, but more durable. That may be a tradeoff that
razor manufacturers are not willing to make.

2\. There are already steel making processes that are designed to make more
homogenous steel. The most famous one is probably CPM (Crucible Particle
Metallurgy):

Instead of pouring an ingot (where the additives have a chance to settle into
a non-homogenous state, they basically pour the steel through something
similar to a shot tower - making lots of tiny homogenous micro-ingots that
they later fuse together in what is essentially a sintering process. The end
result is a much more homogenous ingot. Practical testing shows that steel
made in this way is more performant, although it presumably increases the
manufacturing cost.

~~~
Polylactic_acid
>That may be a tradeoff that razor manufacturers are not willing to make.

Razors are so cheap ($0.10 each) that there is simply no reason to make them
worse in order to last longer when virtually everyone would rather they work
as well as possible and spend another 10 cents a week.

~~~
m463
Unless you are buying gillette blades. Even at costco you can spend almost $50
on a bunch of refills.

Unfortunately I seem to have the best shaving experience with gillette blades.
I tried Harry's and other brands, but then I tried gillette again and it was
markedly better.

~~~
fileeditview
Just buy a good old safety razor. You can then buy some good razor blades for
less than 10 cent a piece or buy the probably sharpest blades on the planet:
"Feather". They are at slightly less than 30 cent a piece.

No matter what you can easily afford a 100 blade pack which will last forever,
create less trash than modern razor blades and with a bit of pratice the shave
will be at least as good.

Other blades I can recommend: Derby Premium (black). They are at about 5€-8€
for a 100 and of good quality and sharpness.

~~~
m463
You know I have, but I have moles on my face and have to be SUPER careful.
With the gillette blades it's always been not only a nice close shave, but I
can do it fast.

~~~
fileeditview
Hehe, my father has a rather big mole on his cheek and I remember that from
time to time he cut it while shaving.. bloody mess!

Take care! :)

------
opwieurposiu
Cartridge razors are garbage, but they are idiot-proof. I use a straight razor
(cuthroat) and hone it a few strokes with 8k diamond after every use, no
leather strop. Even with the time spent sharpening it is faster than a
cartridge razor because it cuts a wider swath and never clogs. It took me
quite a few iterations to find a razor/sharpening tool combo that worked
properly. A safety razor works almost as well with no fuss sharpening. The
other downside of a straight razor is if you drop it could cut your d __* off
so I always put on shorts before shaving.

~~~
catalogia
I like the middle-ground; safety razors. They're exceptionally cheap and idiot
proof. Mine really doesn't clog like cartridge razors either. Cartridge razors
seem like a scam in nearly all respects, although I concede loading them is
probably safer for the elderly or generally those with dexterity problems.

~~~
vl
Safety razor requires more time to shave than cartridge razor because it
requires more strokes. But I actually prefer it because usually I don’t shave
every day. Cartridge razor clogs up in this case. When I shave every day I use
either cartridge razor (Dorco) or wet electrical (Braun 9000). Both work
greatly for daily shaving, fail for shaving every few days.

~~~
Polylactic_acid
You can get a razor that has 3 blades and uses the standard double edge
blades. You just snap them in half inside the wrapping and then load the 1.5
full size razor halves in.

~~~
neilfrndes
Like this one? [https://leafshave.com/](https://leafshave.com/)

I read that it is hard to shave the upper lip area with one of these.

------
ajuc
Not "even the sharpest" but "especially the sharpest". The sharper the edge
the easier it is damaged.

Also - I've got a cheap beard trimming machine I bought 10 years ago. I use it
every week or two, and I haven't replaced the blades even once (I don't think
it's even replacable) - still works fine.

It seems the solution is to use blades that are almost dull?

~~~
fho
Definitely not an expert here but I think the difference is that trimming
machines "cut" by pinching the hair between two moving surfaces. That way you
can have a 90 degree angle at the cutting edge that is much sturdier than a
blade that is designed to cut.

~~~
JeremyNT
This is my understanding as well.

I've tried every form of razor and - despite all the folklore - the best[0]
shaves for me are to be had by _electric_ shavers, which operate on this
principal. These have a foil which the hair can protrude past, then it is
sheered off by either rotating or oscilating "blades" that push the hair
against the foil.

It's like a pair of scissors, which can operate when "dull" \- because there's
something to push against, they don't need to be nearly as sharp.

 _[0] "best" meaning a combination of least discomfort, time efficiency, and
closeness - a safety razor against the grain can get closer, but it's a
miserable experience_

------
jl2718
I assume they mean crystalline domain heterogeneity. The best metals are
single-domain so that there are no fissures along the boundaries. But that
takes very pure material and very slow cooling. A good alternative is
nanacrystalline or amorphous domains, which are fairly simple, just blast with
microwave energy during cooling. This can make a very strong metal with great
working properties, a bit softer, but doesn’t fracture.

------
anitil
Huh, I always thought that it was oxidation from getting wet that damaged the
blade. I even remember getting a recommendation to clean the blade with
alcohol to dry it of faster.

I always find myself falling for this sort of 'Well of course the answer is
<simplified answer that is wrong>'

Edit: I've posted to /r/ImageStabilization/ for that first image -
[https://www.reddit.com/r/ImageStabilization/comments/i54p9s/...](https://www.reddit.com/r/ImageStabilization/comments/i54p9s/could_someone_help_to_stabilize_this_gif_of_hair/)

~~~
aaron695
I palm strop my safety razor, the idea is to smooth the microscopic bumps. No
idea if it's scientific.

[https://www.bruceonshaving.com/2010/11/17/palm-stropping-
raz...](https://www.bruceonshaving.com/2010/11/17/palm-stropping-razor-
blades/)

[edit] Sorry, as Someone1234 points out I actually meant cartridge razor

~~~
gpsx
Cooks use a knife straightener on their knives to keep them sharp longer.
Well, I'm not a cook, but I do it too. It works really well. I was wondering
if people could do this on razors. I think this is equivalent to palm
stropping. For a cartridge, I think something with small metal teeth, at the
right angle, ran back and forth over the blades, would do a good job of
straightening the edges.

~~~
wahern
I suspect cartridge and safety razor blades are too hard (e.g. martensitic or
carbide; see
[https://en.wikipedia.org/wiki/Razor_blade_steel](https://en.wikipedia.org/wiki/Razor_blade_steel))
and too sharp for stropping. That's probably why they're more prone to chip
rather than deform. A good straight razor is made from a softer carbon steel
that, while harder than most stainless steels, isn't quite so brittle. And the
edge isn't as 'razor sharp' as safety and cartridge blades, but more rounded.

I shave with a straight razor, but I'm lazy and use a Feather with disposable
blades. Before that I used aluminum hair shaper blades, like what the barber
uses on the back of your neck (very sharp and thin, but an aluminum alloy).
Such blades are far sharper than a real straight razor and cause razor burn
more easily. I always sort of suspected as much. I tried using a traditional
straight razor several times, but I couldn't get used to it. The feel is just
too different. Several years ago I popped into a barbershop where the owner
did a lot of traditional straight razor work (very rare these days), and he
confirmed everything--a traditional straight razor has a softer, rounder edge
--and disposable blades, like my Feather blades, are far too sharp in his
opinion.

For similar reasons, thinner, harder blades are more likely to nick you
because the microscopic chips tear into your skin more easily. By contrast, as
a traditional straight razor gets dull it stops working as well but doesn't
become more dangerous.

Same thing applies to chef knives. You can use a "steel" on Western knives
because the metal is traditionally softer and has a blunter profile and edge.
(If it's a cheap stainless pressed steel, not uncommon in typical commercial
kitchens--neighborhood joint, not Michelin--you can literally feel the edge
rolled over on a dull knife, which steeling rolls back.) A traditional
Japanese knife is more like a straight razor blade--harder steel, thinner
profile, sharper edge which you maintain with a strop and waterstone--but
still softer and blunter than manufactured razor blades. A cleaver, Western or
Asian, is supposed to be very hard (often a cheap but very high carbon steel)
but also very blunt. You can't steel or strop it; when it gets too dull you
have to grind it or, if you have time to kill, resharpen with a stone.
(Confirmed with a Chinese butcher years ago.)

~~~
KozmoNau7
A steel doesn't roll back a folded over edge, it removes material and sets a
micro-bevel. It's similar to stropping, but with a hard metal tool rather than
a soft leather/denim fabric impregnated with paste. And it's easier to mess up
and dull your knife instead, a knife in reasonable condition really shouldn't
need more than a couple of light strokes on the steel on either side.
Conversely it's almost impossible to over-strop a knife as long as you don't
completely mess up the angle and use too much pressure.

In short, everything you do to work on a knife edge removes material. The
difference is in how aggressively it does it, and to which angle.

If the edge on your knife keeps rolling over or creating a burr just from
using it, you're sharpening it to an angle too acute for the steel to properly
support.

In my experience, by far the most important tool is the strop. I can get dull
knives shaving sharp with a 240-grit stone and a strop in a couple of minutes,
though usually I take my knives to 3000, because it's easier on the strop.

~~~
wahern
Stropping definitely doesn't remove material. It heats the edge which aids in
deforming it back into a more preferable shape as you press into the material
(leather, canvas). If material was removed it'd embed in the strop and
_damage_ your edge, either by chipping or just uneven action.

A strop with paste is a different beast, IMO. You didn't traditionally use a
paste with stropping. I'd bet the rise of pastes, which seem kind of gimmicky,
is related to a loss of traditional expertise and knowledge about the function
of the strop. Relatedly, because of the rise of safety and cartridge razors,
people are accustomed to extremely sharp edges. A _traditional_ straight razor
shave feels harsher--more pressure and pulling--than people expect. Utterly
unrealistic depictions on TV and film don't help, either. For years I thought
I just really sucked at sharpening and honing my traditional straight razors
(one of which is a very expensive Thiers Issard given as a gift), but after
several traditional straight razor shaves at barbershops, which were
_consistently_ harsher than the hairshaper and Feather I normally use, and the
discussion with that one barber who was an expert on straight razors, I
realized it wasn't my poor blade sharpening skills--well, not _just_ my poor
skills. Traditional straight razors just were never meant to be as sharp as
manufactured, disposable blades, and _can 't_ be unless you want to spend more
time maintaining the blade than actually using it. Similarly, if you're
constantly removing material the blade won't last very long as it depletes
beyond a useful profile. Contrast that with wood planes and chisels, which
tend to have very deep, thick profiles because of the need for more frequent
sharpening and material removal; you need that depth so the angle of attack
diminishes less as it shortens, otherwise you'd need to compensate with a more
fragile bevel, which would just accelerate the process.

Steeling might remove some material, especially when used on harder steels,
but in the particular case of pressed stainless I don't think so. (But would
be happy to see evidence to the contrary.) Traditional stainless steels (not
new alloys with, e.g., molybdenum) are _relatively_ soft. It's part of the
reason why they're considered more resilient than traditional steels. They
tend to have higher shear and tensile strength than non-hardened steels;
they'll deform more before they break so they absorb energy better. So, for
example, a stainless steel screw is closer to the resiliency of nails in terms
of sheer strength than regular screws. Moreover, a _pressed_ knife almost by
definition needs to be made of relatively soft metal. One of my first jobs was
working in a kitchen where we used horribly cheap pressed stainless knives for
preparing chicken strips. After slicing a bag of chicken breasts you could
actually feel the edge rolled over, like a letter J. (EDIT: rolled over is a
poor description; if it were completely rolled over deformation by steeling
would never work given the direction of the stroke. Note that the letter J
isn't upturned on my font.) We'd always have to steel the knifes at least once
or twice a shift. If steeling removed that material you'd have metal burrs
everywhere, including in your food.

Maybe steeling traditional Western chef knives does remove material. But if so
I wouldn't be surprised if the benefit is in tearing the edge, effectively
making a micro-serrated edge that works better than an otherwise dulled edge.
Still, I'm dubious that's the primary function if it is at all. Everything
I've read and experienced (as a home cook, at least) is that Western knifes
traditionally use softer steel, and steeling is for deformation/reformation of
the edge without removing material.[1] Steeling a traditional Japanese knife,
or especially a straight razor, is verboten because of the potential for
chipping, macro or micro. I'd never shave with a straight razor that had been
steeled, though I confess I've never tried that specifically.

That said, I admit the purpose and mechanical action of steeling is debated. I
see conflicting discussions (not formal material) all the time, including from
professional chefs, and I try not to discount people's experiences. Plus, it's
not uncommon for the reality of something to differ than the theory even when
the same result (e.g. easier cutting) is obtained. And times have changed.
Modern alloys have different properties than traditional steels, so it's
entirely possible the steeling action is different on many newer knifes than
older ones.

[1] Indeed, IIUC, the very conclusion of the research article suggests that if
steeling worked by cutting material rather than deformation, you'd end up with
significant microchipping and by definition a less sharp and uniform edge.

~~~
KozmoNau7
Abrasion absolutely happens when stropping, however it is very mild compared
to other sharpening/honing processes.

This is by far the best resource I've found for explaining sharpening and the
concepts of sharpness vs. keenness:
[https://scienceofsharp.com/](https://scienceofsharp.com/)

I don't go _nearly_ to that level of effort in sharpening, as I only sharpen
pocket knives, kitchen knives and various tools, I don't bother with straight
razors (or any razors at all, but that's a different matter).

------
yumraj
> “We’ve learned how to make better blades, and now we want to do it.”

Unfortunately this is at odds with the interests of blade manufacturers, so I
doubt we’ll see better blades anytime soon - at least from the current
manufacturers.

~~~
rgoulter
Cartridge razors would surely make more money than safety razors, but people
are still able to buy the latter.

As far as I understand the variety of safety razor blades, there's not a race
to the bottom where the more-expensive blades don't sell.

Insofar as shaving can be a luxury activity, I think it's possible there's
room for more higher price for more durable blades for safety razors.

e.g. The bestsellers here [https://www.amazon.com/Best-Sellers-Beauty-Mens-
Replacement-...](https://www.amazon.com/Best-Sellers-Beauty-Mens-Replacement-
Razor-Blade-Cartridges-Refills/zgbs/beauty/13271084011) lists a pack of 8
refills for cartridge razors for 24 USD. Searching for "safety razor blades"
shows a pack of 100 for 7 USD - 11 USD, and I see a 50 pack for 15 USD.

~~~
Semaphor
> Searching for "safety razor blades" shows a pack of 100 for 7 USD - 11 USD,
> and I see a 50 pack for 15 USD

I once got the Derby blades [0], $5.59 for 100. I still have around 90 of them
left somewhere in the attic because I got what I paid for. Now, I use Feather
blades, about the same price for only 10, but one blade lasts me multiple
month and I get better results. But as you said, with safety razor blades you
only pay a fraction compared to cartridges anyway ;)

[0]: [https://www.amazon.de/Shaving-Factory-Derby-Professional-
Ras...](https://www.amazon.de/Shaving-Factory-Derby-Professional-
Rasierklingen/dp/B00DIW3VHG)

~~~
yumraj
Of the cheaper blades, I really like Astra. For a nicer blade, I prefer
Polsilver over Feather, unfortunately I have had to buy Polsilver from
Bulgaria based sellers via eBay.

Interestingly, the difference between Astra and Polsilver is not much to
warrant the price difference. So, when I'm done with my 100+ Astra and 100+
Polsilver, I'll probably just get more Astra. :)

I pair those with Arko and my shaves have never been better.

------
peterwwillis
I have used straight razors, safety razors, electric razors, and various
cartridges. A good multi-blade cartridge is vastly superior to anything the
layman can do with the first three. They shave all kinds of growth in one
pass, don't cut you, and get very close, without needing any foam. They really
are the pinnacle of shaving technology. It's amazing how people ignore them
for older tech which can only match them with a lot of extra work.

~~~
evanelias
If you have especially curly facial hair, multi-blade razors have a tendency
to yank out some hairs instead of cutting them, especially in places where
some hairs grow in a different direction. This in turn causes irritation,
razor bumps, ingrown hairs, etc.

After using multi-blade cartridges my entire adult life, I switched to a
shavette (disposable blade straight razor) a few months ago and it pretty much
immediately solved all of the skin irritation issues. Plus it's massively less
expensive. The downsides are it's slower and more injury-prone, admittedly.

------
growlist
Wow, amazing imagery. Personally I switched to straight razors recently and
given the very low cost of blades I'm quite happy to use a new one every
couple of shaves, which for me is only once a week.

Edit: sorry, I meant safety razor, not straight.

~~~
Solstinox
You mean double-edge, right? I thought straight edge was basically a shaving
knife you can sharpen...

~~~
growlist
thanks, edited my comment

------
ghaff
I had always assumed based on what I’d heard that corrosion was the main
factor in blades wearing out. Which may still be the case. But this suggests
that there are still ways that soft materials can still chip very thin cutting
surfaces.

~~~
unclebucknasty
Years ago there was some product, essentially a goo, that claimed to
dramatically extend the life of blades. The rationale was that hair was too
soft to dull a blade, and what was really dulling them was oxidation.

Don't know what became of the product, but would be interesting to know if
corrosion plays a role in the chipping.

~~~
ghaff
I vaguely remember way back when I was a Masters engineering grad student, one
of the undergrads had a senior project that involved dipping razors in alcohol
and it significantly increased their lifespan because of reduced corrosion.
And that does seem to be a thing according to the Internet:
[https://macgyverisms.wonderhowto.com/how-to/extend-life-
your...](https://macgyverisms.wonderhowto.com/how-to/extend-life-your-
disposable-razors-keep-them-
sharp-0158954/#:~:text=Stay%20Sharp%20with%20Pure%20Alcohol,sharp%20and%20free%20of%20rust).

Doesn't mean you can't still chip thin edges of a (presumably) fairly brittler
steel blade with something relatively soft of course.

------
taeric
And yet I've been on the same razor for well over a year. Can't help but think
I'm doing something terrible wrong. :(

~~~
throwaway5752
Same here. I use them dozens/hundreds of times. Maybe our facial hair is
softer or we aren't discriminating enough! I notice the difference with a new
blade, but it doesn't bother me.

~~~
ComputerGuru
I think it's a structural difference in the hair itself, along the difference
between diamonds and carbon. I have facial hair that is prone to fracturing
and then giving me splinters that can easily go a few mm deep into my fingers.

~~~
Infernal
I thought I was the only one that got painful beard splinters in my fingers.
Can confirm my facial hair is coarse and wiry, individual hairs seem to
unravel into many strands like a steel cable.

------
1vuio0pswjnm7
"When the hair was free to bend, however, chips were more likely to occur.
These chips most commonly formed in places where the blade edge met the sides
of the hair strands."

So the question is, in shaving, how do we ensure that all hairs are
perpendicular to the blade edge and not free to bend?

I use Feather blades exclusively; the number of shaves I can get from one
blade varies according to the shaving soap used.

~~~
Semaphor
Feather blades are great, but for anyone reading this who thinks about
switching to a safety razor from cartridges or electrical ones: Don’t start
out with them, they are really unforgiving even for safety razor standards in
how easy it is to cut yourself.

~~~
Polylactic_acid
I started with feather blades. Cut myself a bunch the first few times. It
doesn't really hurt but its just annoying because you don't want blood on your
clothes. Eventually looked up a guide and found out I was doing it wrong and
now I basically never have issues.

~~~
Semaphor
Yeah, that’s what I meant. Feather aren’t super hard to use, but they are not
beginner-friendly. It’s easier to learn with other blades.

------
m3kw9
The videos in there are oddly satisfying.

------
tcpekin
Here is the actual article, with much more analysis:

[https://science.sciencemag.org/content/369/6504/689](https://science.sciencemag.org/content/369/6504/689)

------
tyingq
I does ring true that there's little financial incentive to create long
lasting blades.

Even if you produce something that's cheaper over a year, I doubt there are
many takers for the high up front cost.

------
dzonga
before gillete started to market multi-use, multi-blade razors. most folks,
like me who have course curly hair would've only used disposable blades only
once. n I find, single blade razors to be effective, no razor bumps etc. just
wet with water, a light moisturizing oil such as almond n you're done.

~~~
news_to_me
If you like single-blade disposable razors, you'll love a safety razor ;)

~~~
FridgeSeal
I’ve been meaning to buy a decent safety razor setup for a while-any
suggestions for brands or models?

~~~
solraph
Not the GP, but I'd recommend Merkur Classic Safety Razor 33C, or any of the
Merkur models that are generally discussed as beginner friendly, and an
sampler pack of blades.

The sampler pack is key. Every person is different, and every DE razor user I
know uses something different. I won't even tell you what I use, because it's
not relevant.

As a secondary recommendation, shaving brushes and a proper shaving cream /
soap are incredibly worthwhile investments. I usually suggest Proraso as a
cheaper, but still decent starter soap to use until you have a better idea of
what works for you.

------
caseymarquis
I've heard a second hand story about some titanium razors made internally at
<large razor company> which were given out to employees as gifts. They lasted
for years, but could never be released as they simply wouldn't be able to turn
a profit.

~~~
nordsieck
> I've heard a second hand story about some titanium razors made internally at
> <large razor company> which were given out to employees as gifts. They
> lasted for years, but could never be released as they simply wouldn't be
> able to turn a profit.

That seems unlikely to me.

Properly heat treated steel is considerably harder than titanium. This is why
titanium knife blades are generally limited to niche applications (like dive
knives, although that market is being contested by modern rust-proof steels
like H1).

Material hardness is one of the leading factors in edge retention.

~~~
throwaway5752
Seems like a thread where people might be interested in
[https://knifesteelnerds.com/](https://knifesteelnerds.com/), which has made
the front page on HN on a couple of occasions. I have no relationship of any
kind, beyond finding it interesting.

------
ggm
"I liked the scanning tunneling microscope so much.. I bought the company"

------
hendry
Water dulls blades in my experience.

You need to ensure they are dried well after use, otherwise they dull far
quicker. I have no idea why, so perhaps someone can test my hypothesis?

~~~
nordsieck
> Water dulls blades in my experience.

I've heard that corrosion can be particularly damaging to the very edge of
blades. The idea is basically that all corrosion is generally limited to small
surface patches (in the presence of good maintenance) however, the very edge
of the blade has a very high surface area to mass ratio, so corrosion affects
the edge more than anywhere else.

I'd expect any razor that is designed to be around water to be of stainless
steel or some other corrosion resistant material, but I suppose it's possible
that corrosion happens on the edge anyhow (albeit at a much slower rate).

------
lmilcin
Not just human hair. I use razors to scar bread loves before baking them.
Surprisingly, the razors get dull quite quickly after couple dozen loves.

------
xmprt
When manufacturers make more money by selling more blades, I don't think
they're going to invest much into this technology anytime soon.

~~~
keenmaster
Unlike with mature tech platforms, successful entry into the market is not
exceedingly difficult. A new company can offer everlasting razors. Then
cleaning cartridges and other refills will become the new razors.

------
wrycoder
Research probably funded with government grant.

They patent it, either start a company or collect royalties. MIT takes a cut.
Standard MIT practice.

~~~
s1artibartfast
and everybody benefits.

~~~
wrycoder
Not if you’re a taxpayer that would rather not fund such things.

In other words, the government grant should at least be refunded from the
profits.

~~~
s1artibartfast
That is a reasonable opinion to hold, as long as you understand that direct
financial profit not the purpose of nearly all government spending.

The intended return on investment is the knowledge generated by scientific
research, as is maintaining the scientific research pipeline and subsidizing
academics. More profit for MIT and corporations is also a positive outcome, as
is better razors for US consumers.

If most voters believe this is a net positive, they can sign the rest up to
pay for it in our democratic system.

------
aidenn0
I wonder if powder metallurgy blades last longer considering they tend to make
more homogeneous alloys

------
natmaka
Isn't strain-hardening also a factor?

------
Markoff
Looking at the first photo - aren't you supposed to shave against the growth
of hair?

I use hair clippers, clean shaving is for babies.

~~~
m463
I shave with the hair at first, then against it.

------
known
Pythagoras theorem in play;

------
tus88
I would like to know this too.

