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Guest Post
Professor John Verhoeven contacted me recently about a small study he did about how razor blades dull. Dr. Verhoeven is well known in the knife community for writing Steel Metallurgy for the Non-Metallurgist, a now classic text introducing metallurgy to knifemakers and bladesmiths. And for his work on Wootz Damascus; I reviewed his book Damascus steel Swords: Solving the Mystery of How to Make Them. This recent study on razor blades was to look at the contribution of micro-chipping on the dulling of razor blades, as a popular journal article recently came out on this mechanism, published in Science. I found Professor Verhoeven’s findings very interesting and offered to publish them on this website. So enough of my commentary, on to his article.
Abstract
Razor blades can dull by 4 mechanisms, corrosion of the steel, wear from contact with whiskers, formation of evaporites due to inadequate drying and the microchipping formation produced by contacts with whiskers. The last mechanism was only recently discovered [2] and the purpose of this study was to determine if microchip formation plays a significant role in dulling razor blades during shaving. Experiments have been carried out with properly cleaned blades showing that after as many as 140 shaves the fraction of the blade length occupied by microchips was still not sufficient to give rise to a significant reduction in shaving smoothness.
Introduction
The double edge razor was invented by Gillette in 1904 and was the most popular blade into the early 1970s. The blades were made of carbon steel and coated with an oily substance to avoid corrosion. In the early 1960s the British firm, Wilkinson Sword, began using stainless steel blades and the large American companies quickly followed suit. In 1971 Gillette introduced the cartridge razor which contained 2 very narrow blades packaged in a cartridge that could be easily removed from a handle. They are now produced by several different companies and have evolved into cartridges with 3 to 5 blades. The blades are made of a martensitic stainless steel and the sharpened edges are coated with a polyfloride to reduce friction and the cartridges contain one or more lubricating strips that purportedly make for a smoother shave. The Gillette Mach 3, which the author uses, has a moisturizing strip above the 3 blades which releases a blue substance to reduce friction but becomes significantly depleted after around a dozen shaves. The cartridge razor blades are now the most popular type of razor.
The martensitic stainless steel used in the cartridge razor blades has a composition of around 12-13 % Cr and 0.6 % C and is heat treated to hardnesses of around 62-3 Rockwell C. The steel contains very small spherically shaped Cr carbides distributed throughout the interior. Two Swedish steel companies supply much of the steel, Uddeholm and Sandvik. See ref. [1] for a more detailed discussion of these steels and why their composition optimizes hardness while maintaining good corrosion resistance. The steel is supplied from the mill as thin strips. The hardness of whisker hair is much less than that of the steel and one would expect wear of the steel would be very small. Reference [2] presents hardness data of whiskers showing them to be softer than the blades by a factor of 50. The edge of a razor blade is sharpened to a very small radius, on the order of 0.2 microns [3, p.6]. Wear would be expected to round the sharp edge and dull the blade. But because the blades are 50 times harder than the hair follicles, one would not expect much wear during shaving.
There are two obvious ways that these steel razor blade would dull, wear on repeated contact with whiskers and corrosion of the steel at the sharpened edge. However, there is an additional mechanism causing blades to dull that is not well recognized. Most water supplies have some level of mineral impurities in them, notably carbonates. If this water is left on the edge of a blade after shaving, in addition to promoting corrosion, it will evaporate and leave a thin layer of an evaporite, such as calcium carbonate on the cutting edge which will dull the blade. The cartridge razors with 3 to 5 blades are difficult to dry properly due to the small distance between blades and are subject to dulling if the water is not removed from the blades prior to evaporation. There is a wide perception on the internet that the cartridges need to be replaced after only a week or two, following is a quote from the web:
On average, a man shaving daily should expect his razor blade to last around a week. This means that a razor blade will need changing after about 6 shaves if you shave using the three-pass technique (with the grain, across and against). May 17, 2019.
A recent article in the magazine Wired [4] states that the blades usually last a week or two before they start to pull and are discarded.
A few years back, after removing the blades from the cartridge and finding evaporite deposits on their back side, the author began drying his 3-blade cartridges immediately after each shave. The procedure was as follows: The cartridge was held in a rapid stream of hot water from the faucet followed by shaking to remove water and drying by tamping both sides with a high knap towel followed by blowing to remove trapped water and further towel drying to remove any breath moisture. The author found that he could use the cartridges for many months before noticeable pull became a problem. This ability of adequate cleaning following each shave, to allow the cartridge blades to be used for several months with no significant loss of shaving comfort, has been found by others as reported on the web [5].
Recently a group of researchers at MIT [2] published an important article describing an elegant set of experiments carried out inside a scanning electron microscope in which the cutting action of a blade could be observed. They found that the hair strands, even though much softer than the steel blades, cause microchipping to occur. The present study was done to determine if microchip formation plays a role in the dulling of cartridge razor blades. It is possible to easily examine the cutting edge of the cartridge blades in an optical microscope with an inverted stage. When the cartridge is place on the horizontal stage the ground edges of the blades are viewed at right angles and one can obtain high magnification views perpendicular to the edge. Figure 1 presents a micrograph of one of the Mach 3 blade edges in a new cartridge. The micrograph of Fig. 1 was taken with a 50x objective lens. The microchips detected in the study [2] were found to have dimensions that were a significant fraction of the hair follicle’s diameter, reported to range from 80 to 200 microns. If the hair follicles of the author’s beard are producing microchips on the blades of the Mach 3 cartridges, such microchips should be detectable upon examination in the optical microscope upon micrographs such as that of Fig. 1. (Note: The author has measured the diameter of 3 of his face hair follicles. They ranged from 100 to 140 microns.) Data is presented here on examination of two Mach 3 cartridges used by the author in which the cartridges were cleaned after each shave as described above, one cartridge after a short-term use and the other after a long-term use.
Short term study
In this study all 3 blades in the Mach 3 cartridge were examined in the optical microscope with the 50x objective after repeated intervals of around 10 shaves in which the cartridges were cleaned as described above. The individual blades are labelled here as, leading, middle and trailing for the 3 blades to identify the order in which they cut the whiskers. They were examined along a 21.5 mm length at the center of their 34 mm lengths. Figure 2 presents micrographs of the edge of the blades containing chips numbered 1 and 2. The blade edges located away from the chips were indistinguishable from that of the new blades as may be seen by comparison to Figure. 1.
The lengths of the chips along the edge were measured on each chip and Fig. 3 presents data on both the number of chips formed and total chip length along the 3 blades versus the number of shaves in the study. It is seen that the number of chips gradually increases with the number of shaves, while the total chip length suddenly rises during the last 10 shaves. This sudden rise was due to the formation of a large chip on the middle blade.
Table 1 presents the data on the chip length of the 12 chips formed during the 60 shaves of study 1. It shows that after 60 shaves the fraction of the total length over the 3 blades occupied by chips is 0.017.
Long term study
Prior to publication of reference 1 the author had been using a Mach 3 cartridge for 10 months, shaving every other day for roughly 140 shaves employing the drying technique presented above. This cartridge has been examined in the optical microscope as described above with the following results: Figure 4 shows the edge of a blade after 140 shaves located away from chips. It may be compared to the new blade shown in Fig. 1. It is apparent that in these images of the blade edges, taken at a 90 degree angle to the blade surface, that there is no indication of wear of the old blade along its edge at locations away from microchips after 140 shaves.
Table 2 presents the data on the chip length from this study. One sees that the number of chips has increased from 12 in the short-term study to 43. Table 3 is presented to illustrate the distribution of chip length in the two studies. It is seen that in both studies the majority of chips have lengths between 7 and 51 microns. Interestingly, the number of chips on the leading blade was found to be significantly less than the middle and trailing blades in each study.
Summary and Conclusions
To estimate the loss of smoothness after each study the author shaved half of his face with a new cartridge blade and the other half with the old one. In the short-term study, he detected no loss of smoothness and in the long-term study only a very slight loss. The purpose of these studies was to determine if the microchipping discovered in ref. [2] was the cause of the perception on the web that cartridge blades needed to be replaced after 6 to 12 shaves. With properly cleaned blades chip formation only dulls the blades on that fraction of the blade where they have formed. This study has shown that the microchipping predicted by [2] does occur during shaving with cartridge blades. However, it also shows that the fraction of the total blade length in the cartridge does not produce a significant loss of smoothness in cartridges that have chip fractions as high as 0.056 after 140 shaves. The study supports the hypothesis that the reason many men discard their cartridge blade after 1 to 2 weeks is because the cartridges are not properly cleaned after each shave and not because of microchip formation.
References
[1] J.D. Verhoeven, Steel Metallurgy for the Non-Metallurgist, ASM International, 2007, p. 143 and p. 211.
[2] G. Rosdioli, S. Mohadeseh, T. Mousavi and C.C. Tasan, How Hair Deforms Steel, Science, 2020, 369, p. 689-694.
[3] J.D. Verhoeven, Experiments on Knife Sharpening, 2004, https://www.relentlessknives.com/newsletter_files/KnifeShExps.pdf, Accessed Dec. 2020.
[4] https://www.wired.com/story/why-do-razor-blades-dull-so-quickly/ Accessed Dec. 2020.
[5] https://www.smarticular.net/en/this-simple-tip-will-make-your-disposable-razors-last-for-months/ Accessed Dec. 2020.
My experience on earlier straight-razors of mine, where I still aimed for RC 59-60… sigh was that they would get very scratchy if I angled the blade against the skin, to get a more aggressive shave, half my face and I would have to strop… with compound to get it smooth again… it went away when I started keeping the blade flat against my skin… i notice it less, now that I aim for Rc63 ish on O1… I strop mainly to clean the edge after rinsing… I wonder if that could be a factor, I don’t have to do two passes if I angle a blade, but it seems to degrade the edge quite a bit. I don’t believe I have a particularly coarse beard
The Science article talked a lot about the angle of the razor so maybe you are on to something.
This certainly sounds plausible or even expected a priori; the amount of stress on the steel will change a lot if you change the angle.
Something you might want to consider is honing a separate razor to a higher angle for the parts of your face where you want to angle the blade for a more aggressive shave. The strength of the edge goes up pretty quickly with the inclusive angle, so a bit higher of an angle might make a large difference.
I wonder what the results look like with high alloy s110v blades, or ceramic blades
I’m saying this in a good way. Thank you for looking into this. I like that there is a place that digs deep, uses the scientific method within the bounds possible, and generating fascinating observations and results.
I’m looking forward to a followup that examines the “cleaning hypothesis” specifically, looking at cleaned vs. uncleaned blades over their lifetime.
I find this a really worthwhile topic. I also have used gillette mach3 cartridges until the ‘planned obsolecense strip’ falls apart. I try to ‘strop’ them against my palm at least 50 times before and after shaving, which would fit with John’s hypothesis about edge deposits. My feeling was that it had to do with maintaining whatever ultra hard coating was on the blades but cleaning might make more sense.
I think the point that the total edge length effected by chipping is too small to make a difference seems reasonable, but I wonder if optical microscopy is not good enough to really appreciate the extent of the damage done by super tiny chips. Has anyone actually been in touch with the MIT team ?
The other authority I’d love to heuar contribute to this would be Todd of science of sharp. His images definitly seem to show microchipping at sizes significantly below 7 microns.
I also thought the moving images of cutting dynamics on the MIT site clearly illustrated the loads generated by hair cutting ; just like abusing a knife by cutting a very tough but not hard material the edge is seen to dig in and then gets torqued by the movement of the material being cut. I’d propose that the reason for less damage on the leading blade of a multi blade cartridge is that even though it is cutting more hair, the trailing edges might be seeing more abusive loads as the very short beard hairs in the skin now under tension from the drag of the first blade are able to exert more force than the longer hair.
On the steel front, it would seem that the balance of wear resistance to strength is really important. It would seem razors are already made from stainless steels able to attain high hardness and strength, so it would seem hard to improve very much, perhaps aiming for the absolute minimum carbide volume to achieve high hardness.
Thanks again,
The chips observed by Dr. Verhoeven are similar in size to those reported in the Science paper. You can read a comment from Todd here: https://bladeforums.com/threads/is-micro-chipping-the-cause-of-dull-razors.1769466/page-2#post-20290885
Indeed, that is insightful. Though one would expect that the flexing and pulling behavior of the hit under the for es of cutting would be qualitatively similar, just reduced substantially in magnitude.
I can also add that I shave in the shower and have a light beard, so am a good candidate to start with for long razor life.
Another strike against the chipping hypothesis is that unless I’m missing something the sort of light stropping normally done before shaving with a straight razor is insufficient to really repair these chips, and one normally needs to hone that straight razor less frequently than one would replace a cartridge razor. I know Todd has mentioned that the layer of oil deposited by stropping on leather is important to shave quality so the lack of maintenance of that coating with safety razors might also contribute (is it build up of minerals or loss of oil\wax\teflon and surface oxidation )
It’s important to understand that shaving, like many types of mechanical separation involves two steps; initiating the cut and completing the separation. These two steps involve different microscopic mechanisms, and rely on different properties of the blade for their efficacy.
Uncomfortable shaving, or ”tugging” happens when the blade is keen enough to initiate the cut, but has lost the properties that reduce the effort in completing the cut. In the case of razors, this is often the lubricant on the bevel. In normal use, cleaning the blade removes debris that would otherwise increase the effort of completing the cut. In the extreme case, a dull blade can “shave” with extreme comfort because it never catches a whisker so there can be no tugging.
An example of this can be experienced by purchasing Feather “carbon” DE blades – these are just as keen as the standard blades but don’t have the fluorocarbon coating. While the standard coated blades shave effortlessly, the uncoated blades tug and pull whiskers out by the roots.
Along with making tools, I’m a long-time straight razor user. A decade ago, I tried some of the “wondersteel” razors, from the early “tungsten steel” razors to more recent offerings (and some intermediate like friodur).
Time and again, the plain “silver steel” razors medium temper or medium hard (which probably equates to about 62/63) exhibits a great combination of strength and toughness. Harder, and the razors don’t hone quite right and can fail to survive a linen. Softer, and they need more time on the linen before the edge is worn well enough for them to hold (and get below 60 or so, they just aren’t very good).
I started looking at edges under a microscope and found the same as the guys did above, but I’m sure this isn’t news to the razor industry. The hard coatings make new blades hold up OKAY but they deflect and if enough, then chip. If you hone past the plating, the steel underneath is soft and the angle has to be increased. If you’re willing to do that with a disposable razor blade, you can use a submicron oxide and shave indefinitely, but it’s like shaving with a 2 week old disposable blade that has no snags. You have to shave every day else the hairs start to lay over and the razor won’t get them.
That’s predictable. The real puzzler to get a good razor blade out of stainless is to get something fine enough that it will hold 63 hardness at 16 degrees (not sure if that’s possible) without needing the coating. I’m convinced also after testing plane irons and noticing that XHP has less friction that part of the reason for the chromium coating is that it’s very slick and it can make a dulling razor feel more smooth than it really is (by sliding across the face easier – you can’t really discern resistance on a straight razor due to sharpness from that created by a fat bevel on a fatter grind – on steel, that can be felt).
The longer you shave, the better you get a sense for these things (with exposure) and you start to notice that the finest razors are relatively pedestrian “silver steel” but with extremely skillful grinds that leave some weight in the spine and a very fine bevel (one that takes less effort to sharpen, but is big enough to keep edge failure from passing the bevel, and one that is small in contact with the face).
…and suddenly everyone from the past isn’t so “backwards and dumb”.
Nobody makes a straight razor equivalent to the best made around, say, 1920 in germany or 1960 in japan, and the bonkers high hardness razors aren’t the best.
(there’s no economic incentive to solve the issue of making a high hardness stainless that would last four times as long in a disposable razor, either).
I’ve been cleaning and drying my disposable razors for many years. I’m on my last razor of a 12 pack I bought close to 3 years ago.
My wife was complaining about razor blade life. Told her to clean and dry it after each use and stop leaving it in the shower. She was amazed. Her razor life went from one or two shaves to dozens.
A good dose of common sense goes a long way. Water damages metals; Metal lasts longer when kept clean and dry; clean and dry your Metal bladed razor; it will last longer.
Hell, what doesn’t last longer when kept clean and dry?
This seems a bit disingenuous though:
“the author began drying his 3-blade cartridges immediately after each shave […] This ability of adequate cleaning following each shave, to allow the cartridge blades to be used for several months with no significant loss of shaving comfort, has been found by others as reported on the web [5].”
[5] is an article about stropping razor blades over some blue jeans and THEN rinsing them with water, which is not wiped off but allowed to dry on its own. This is very much not the same process as that used by dr. Verhoeven. And most of the comments on there agree with the stropping part, not with anything about drying. The few that mention any sort of cleaning are about removing stuck hairs with a brush, so again nothing about drying the blade. So [5] doesn’t seem to actually support the paragraph it’s cited in.
Over 50 years of shaving and NOW they tell me!
“The martensitic stainless steel used in the cartridge razor blades has a composition of around 12-13 % Cr and 0.6 % C and is heat treated to hardnesses of around 62-3 Rockwell C. The steel contains very small spherically shaped Cr carbides distributed throughout the interior.”
How would these steels perform as kitchen knife steels? Are they similar to anything available?
Yes you would look for kitchen knives in AEB-L, 13C26, 14C28N, or 12C27.
It’s good to know that a razor blade should be changed after about 6 uses. My razors have been dulling a lot quicker lately. I think it would be a good idea to find a new brand to buy from.
I use my hair dryer up against the blade for about 1 minute. Easy peasy and the gilette lasts 4-6+ months.