Does rinsing the razor in cold water improve the cut?

MadAd

Senior member
Oct 1, 2000
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Is the difference in cold tap water, and water from the hot tap enough to blunt the cut of a cheap razor?

We hear the term cold steel, and sure enough if we think about a sharpened edge then some heat expansion would certainly alter any point constructed at the blade tip, but is it going to be negligible?

I mean can I give up shaving in cold water because of some belief I inherited that it cuts better?

Not being that up on thermodynamics I cannot begin to evaluate the difference. What say you guys?
 

TuxDave

Lifer
Oct 8, 2002
10,572
3
71
You shave in cold water? O_O I shave using warm water cuz I feel like the hair is easier to cut when it's warmed up.
 

Crusty

Lifer
Sep 30, 2001
12,684
2
81
A warm razor helps keep the pores open which makes the hairs easier to cut.. at least that's what I've always thought!
 

Paperdoc

Platinum Member
Aug 17, 2006
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The water temperatgure will make NO difference in the sharpness of the blade. "Cold Steel" refers to a particular sequence of processes in the manufacture of the steel: it is mechanically pounded into shape while room temperature, rather than very hot. This can produce a steel which is hard enough to keep a very sharp edge after it is sharpened later. The phrase has nothing to do with the temperature of the blade during actual use.
 

bobsmith1492

Diamond Member
Feb 21, 2004
3,875
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Originally posted by: Paperdoc
The water temperatgure will make NO difference in the sharpness of the blade. "Cold Steel" refers to a particular sequence of processes in the manufacture of the steel: it is mechanically pounded into shape while room temperature, rather than very hot. This can produce a steel which is hard enough to keep a very sharp edge after it is sharpened later. The phrase has nothing to do with the temperature of the blade during actual use.

Actually I thought it was more of a colloquialism having to do with swords - "the ring of cold steel on steel" and so on (steel feels cold to the touch, after all).
 

MadAd

Senior member
Oct 1, 2000
428
1
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Ok but but but

So if hot water is applied to these tinny bits of metal they call a blade, its not going to expand sufficiently to affect the bluntness?

Ok, no code tag, this is going to be fraught with danger, but I will attempt to ascii draw an exaggerated picture what I mean.

/|
to
_
/ |

..or

/
to
_
/

(EDIT: *sigh* it wont put the other \ in the bottom 2, oh my kingdom for code tag)

Depending on if the blade has one flat side, or both come to a point, surely if the metal expands a little, its going to leave a flat spot at the tip no?


(oh and its only the rinsing the blade bit I do in cold, the wash pre foam i use warm- im not THAT much of a masochist :-0 )

And thanks to Paperdoc for the proper explanation of the term Cold Steel, that makes sense.
 

Paperdoc

Platinum Member
Aug 17, 2006
2,298
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No, thermal expansion will not have any significant effect on the edge sharpness. You were drawing something, I think, that expanded horizontally so that the bevelled side is pushed away from the straight side, thus making the very tip wider. But it expands in ALL directions almost the same. Think more like a balloon with a sharp edge (I know, this really does require imagination!). If you inflate it more, everything expands outward, and the edge is still wedge-shaped and sharp. Well, not quite, I realize - the very tip of the wedge will start to get a bit rounder than it was. But the change in tip roundness is small, and it is VERY small if the extra expansion is only a little bit. And that is what happens when you heat the razor blade from 40 F (pretty cool water) to, say 140 F (that's hot enough to be in danger of burning you if you run it over your hand). The associated expansion is quite small.

I don't have a reference here with the thermal expansion coefficients of steels. But think of this: ralroad track sections. To allow for the extremes of shortest (at -40 F) to longest (at +100 F) lengths, the rails are laid with a small gap at the end of each. That gap is less than ¼" for a piece of rail that must be 60 feet long (or 720"). That's a maximum expansion range of about 1 part in 3,000. Small.
 

ScottMac

Moderator<br>Networking<br>Elite member
Mar 19, 2001
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Thiers Issard, maker of high-quality straight razors, suggests rinsing the razor in hot water before you begin shaving (the same hot water used to prep your suds and face).

If I can find the literature that came with one of my razors, I'll post it up.

Other preferences and procedures can be found at the StraightRazorPlace.com site or BadgerandBlade.com.

In all cases, the strop and shave is done with warm / hot blades.

In general, the process is:

Soak your face hot (out of the shower, hot steamy towels, etc)
Apply the warm suds / shaving cream / whatever
shave with, across, against the grain ... any or all ... your preference
Apply cold water to close the skin pores
Optional application of Alum from an alum block to close pores & minor bleeder mitigation
Wash the alum off with warm water
After Shave / Balm

FWIW

 

Soulkeeper

Diamond Member
Nov 23, 2001
6,712
142
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the cold water could make your hair folicals and skin tighten up which would make the hair easier to cut ...
 

KIAman

Diamond Member
Mar 7, 2001
3,342
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No.

Unless your pores react to a 10 degree f temperature difference and has a super fast reaction time (by the time the razor is touching the skin, it is already cutting the hair).

No.

There is no property of steel that changes with such a minuscule temperature change.

As to expansion, steel expands at a rate of 7.3 micro(millionth) inches per degree F. Human hair is anywhere from 669 to 7125 micro inches in diameter with the average somewhere around 4000 micro inches. Just to give some perspective.
 

futuristicmonkey

Golden Member
Feb 29, 2004
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Originally posted by: KIAman
No.

Unless your pores react to a 10 degree f temperature difference and has a super fast reaction time (by the time the razor is touching the skin, it is already cutting the hair).

No.

There is no property of steel that changes with such a minuscule temperature change.

As to expansion, steel expands at a rate of 7.3 micro(millionth) inches per degree F. Human hair is anywhere from 669 to 7125 micro inches in diameter with the average somewhere around 4000 micro inches. Just to give some perspective.

Micro inches? Hey buddy, its either the metric system or that other mess...not BOTH!




:p
 

ScottMac

Moderator<br>Networking<br>Elite member
Mar 19, 2001
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Originally posted by: Soulkeeper
the cold water could make your hair folicals and skin tighten up which would make the hair easier to cut ...

Would you like to behead a face-full of goosebumps?



Soften the hair, open the pores, cut, then close the pores and seal off the bleeders.

People have been doing this for centuries. They got it down.

If you really want to see it done right, go to a Truefitt & Hill barber shop (US$25.00 + tip for just the shave)

 

silverpig

Lifer
Jul 29, 2001
27,709
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Originally posted by: KIAman
No.

Unless your pores react to a 10 degree f temperature difference and has a super fast reaction time (by the time the razor is touching the skin, it is already cutting the hair).

No.

There is no property of steel that changes with such a minuscule temperature change.

As to expansion, steel expands at a rate of 7.3 micro(millionth) inches per degree F. Human hair is anywhere from 669 to 7125 micro inches in diameter with the average somewhere around 4000 micro inches. Just to give some perspective.

Those numbers don't make sense. You probably mean 7.3 microinches/inch or something.

I find it hard to believe that a 1 inch piece of steel and a 2km long piece of steel will both expand by 7.3 millionths of an inch if heated by 1 deg F.
 

Soulkeeper

Diamond Member
Nov 23, 2001
6,712
142
106
personally i just shave and get it over with, i don't have time to let water heat up or put girly-man moisturizing shaving creme on my face
i like my skin rough and dry like a man's skin should be, i don't need a moist face to google about microinches or whatever ....


 

PolymerTim

Senior member
Apr 29, 2002
383
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Originally posted by: silverpig
Originally posted by: KIAman
No.

Unless your pores react to a 10 degree f temperature difference and has a super fast reaction time (by the time the razor is touching the skin, it is already cutting the hair).

No.

There is no property of steel that changes with such a minuscule temperature change.

As to expansion, steel expands at a rate of 7.3 micro(millionth) inches per degree F. Human hair is anywhere from 669 to 7125 micro inches in diameter with the average somewhere around 4000 micro inches. Just to give some perspective.

Those numbers don't make sense. You probably mean 7.3 microinches/inch or something.

I find it hard to believe that a 1 inch piece of steel and a 2km long piece of steel will both expand by 7.3 millionths of an inch if heated by 1 deg F.

Yup, it's length over length with a temperature term. I'm American myself, but for anything scientific, I much prefer metric, so here's the numbers for those interested:
Steel 13 um per meter per degree celsius.
http://www.engineeringtoolbox....coefficients-d_95.html
Note this is linear thermal expansion. You could also consider volumetric expansion. But I agree with others that most of this expansion will be isotropic and have negligible effect on the bluntness of the blade.

Quick calculation:
Assuming a typical razor edge radius of 0.1um (source), expanded over a 100 degC temperature range will give
0.1*(1+13E-6) = 0.1000013 or a change of 0.0013%
EDIT:
MadAd's response made me realize I forgot the temperature factor, so multiply the above answers by 100 degC to get 0.10013 or a change of 0.13%. :eek:
/EDIT


Of course, this is not to minimize the effect of thermal expansion in general. They can actually be quite severe since the forces generated can be very high, they just don't happen to be very important in this particular application.
 

MadAd

Senior member
Oct 1, 2000
428
1
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0.0013%!!!

Thats the bottom line? Ok thats not much really, and thats over the full spectrum of 0 to 100, in real terms it'll be be much less.

jeez I love this place, where else could I get such a perfectly technical answer to such a common everyday thing? :D Thank you all.
 

PolymerTim

Senior member
Apr 29, 2002
383
0
0
Originally posted by: MadAd
0.0013%!!!

Thats the bottom line? Ok thats not much really, and thats over the full spectrum of 0 to 100, in real terms it'll be be much less.

jeez I love this place, where else could I get such a perfectly technical answer to such a common everyday thing? :D Thank you all.

Oops :eek: Actually I did forget the temperature term in the final calculation. Numbers corrected above.

Originally posted by: crazychicken
micro inches is not mixing systems... micro just means e-6

ie. 1 micro inch = .000001 inches
I think he is referring to micro not commonly being associated with non-SI units. Although, technically, I don't think there's anything wrong with it, I can see how some might consider it mixing units. I'm not really sure if the US or Imperial systems of measure even have a unit that goes this small. The smallest one I've encountered is the "mil" or, less commonly "thou," referring to a thousandth of an inch. Interestingly, this term is derived from milli-inch and so might be considered a mixed term as well.
 

KIAman

Diamond Member
Mar 7, 2001
3,342
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Originally posted by: silverpig
Those numbers don't make sense. You probably mean 7.3 microinches/inch or something.

I find it hard to believe that a 1 inch piece of steel and a 2km long piece of steel will both expand by 7.3 millionths of an inch if heated by 1 deg F.

Yes, thanks for the correction. It is 7.3 microinches/inch per degree F.

As to my use of non-SI units, I tend to tailor my response to the content of the question. In this case, the question was worded in a way that I felt a non-SI perspective between the expansion of steel and the average thickness of human hair was appropriate.