Thread: Blade Temperature

In the 1990 Cohen Brothers classic film "Miller's Crossing", we enter directly into a scene where Johnny Caspar, a 40's crime boss played by Jon Polito, is arguing with his bodyguard about the temperature of a shave. We all know hot water is our friend, but Caspar's argument is about the blade. He says the steel is firmer and will hold it's edge longer if it's colder than if it's warmer. His goon's opinion is that anybody who puts the blade before his skin has got his priorities out of order.

I imagine those characters use straight razors and I can't help thinking about how they might both be right. Given that hot water is a good thing for the face, How will the steel (normal carbon say) respond to hot vs. cold water during the shave? It would be just as easy to rinse the blade with cool water and if will increase the edge holding capacity throughout the shave I'd be in heaven. That cold steel might be reason enough to try, but I don't want to ruin the edge either. Part of me thinks that the warm blade might have a bit more spring to it and that that might be a benefit somehow.

How would changing the temperature of the blade between say 10 - 40 ºC (50 - 100ºF) change the nature of the shave?
1. edge retension during the shave?
2. edge lifespan before honing?
3. skin response if any?
???

Well I'm no metalurgist but it doesn't seem to me that a narrow range like that should have any real difference in changing the molecular characteristics of the steel in the razor. It may very well affect the skin and wiskers though during the shave.

I always rinse my razor under hot water (about 130F) before shaving and during the shave and have been doing it for years and have noticed no bad influence on the steel. I've never used cold water or ice water though.

IMHO, of course, but 50/100 degrees means nothing to tempered steel. The only possible difference temperature could make to a steel is way more extreme than that. At a very cold temperature, meaning near cryogenic ~ maybe, as long as it doesn't shatter, but at the fraction of a millimeter thickness at the very edge of a razor where it counts, it would warm almost instantaneously when it meets your face. Temperature change of steel at that thin edge is so rapid, no matter what you do to it it equalizes very quickly. I think the more important thing is the temperature of the blade in it's entirety, and that is purely for comfort. Personally I dip my blade in hot water before I begin my shave, but that's just because I'd rather have warm steel on my face than cold. As far as affecting the performance of the blade.....I doubt it.

Am guessing at this, but .....

As the edge is so thin, wouldn't even a small change in the temperature make a difference? The warmer it is the more it should "extend", thus making the cutting edge microscopically longer and thinner. I could be completely wrong but I think that a warm blade should cut slightly better.

(Ok, start shooting if it is nonsense).

Hoekie

Now we're talking and you have a great point about the "lengthening" that I hadn't considered, Hoekie. I wondered how much spring the fins would lose if they cool and whether it's a bad thing or not for their cutting action.

X

Hoekie is certainly correct about the expansion/contraction of the metal... a 3-inch razor blade will expand about 1 one-thousandths of an inch for a 20-degC raise in temp. The expansion/contraction is linear unless there are stresses in the metal (and there almost always are) in which case there will be deformities (curling, buckling, etc.).

It's hard to imagine there is much effect on a razor's edge... but a while back I began to think my razor got dull when I rinsed it in hot water while shaving so I started wiping the lather off with my finger and flicking it in the sink. I never thought much more about it... but now that I do, I'm guessing there could be significant stresses built up in the edge due to the rapid increase in temperature induced by rinsing in HOT water which would warm the edge faster than the thicker part of the blade. And, it makes my head hurt thinking about it.

As an aside... In another life I did some computer automation of the machine shops for a manufacturer of military equipment. The shops were not air conditioned -- in the winter it was cool and in the summers warm (say a range of 50 to 100-degF). Because of the close tolerances needed, they had different programs for (as nearly as I can remember) each 10-degF temperature change. Some of the parts were produced on a 90-foot long milling machine made, predominantly, of cast iron. The parts being produced were titanium, which has a much different coefficient of expansion than iron. Thus, for a given temperature change, the machine would expand/shrink a different amount than the part being made -- hence, the need to adjust dimensions.

Azjoe,
We use the same thing here in our machine shop. We do some tight tolerance bearing housings, + or - .0005 ( 5 tenths) and have a calculator program with the coefficient of expansion factored in for ever degree difference between the shop and the inspection area.

That 1 one thousanth of an inch is over the 3 inch length. Over the 5/8 width is is even smaller and that is for a 10 deg. C change.

Tony

The paperwork on my TI's tells me to run the blade under hot water before a shave to get the best shave. Maby it is how the skin reacts to a warm or cold blade?

Mason

After pondering on it for a bit .....

So we established that the razor should be sharper when warm.

Now to continue my guess-work:

A cold blade should stay "sharper" longer (making sure x=y, x being warm sharpness and y being cold sharpness).

Why do I think so?

If x=y it means that when both are resting and at the same "cold" temperature, in comparison the warm blade will have shrunk a bit, thus becoming a bit more blunt.

To add to this is the fact that the thin warm blade would be more vulnerable for damaging (lesser density of material).

(Again, if nonsense please shoot)

How much this all affects your shave all depends on the defenition of "sharp enough" I guess.

Hoekie

A lifetime or two ago in Vietnam somebody told me that I would suffer less razor burn if I rinsed the blade in cold water before shaving. I was shaving with a DE then and started doing that and found it was true. I continued it with twin and M3 razors for years, always with great success. I have recently switched back to a DE and am using a straight occasionally. For some reason I just automatically went to rinsing the blade in hot water after all these years, without giving it much thought. Now that the subject has come up, I think I will give the cold water another try.