The Science Of Blade Sharpness

How do you know what works well for you when shaving? How did you come about your best? How well can you compare and contrast the performance of the blades you use and swap out on a regular basis?  A blade is a blade is a blade, right?

Blade Consistency

When you examine the myriad of razor blade reviews on yee olde internets, what do you usually find?  You get one man’s opinion as to how well that blade works for him alone. This is better than nothing but may not be the best guideposts as to what will work for you and your unique situation.

What if I could have you examine a few charts and graphs and get a better idea of what blades give you the most consistent results? If you stick with me throughout this short article I will explain why certain blades are more comfortable to work with and scientifically prove which blades are better.

Most of the data for this article comes from www.RefinedShave.com.  The gentleman who has produced that wonderful webpage has brought scientific testing to the arena of double edge razor blades, so we might get a glimpse of how various brands and blades perform from the first time you pick them up until the time you recycle them. As a fair disclaimer, the author that webpage is an engineer, as am I also, but I’m not affiliated with him nor have I been in direct contact with him. We will simply examine the data that he provides and draw conclusions thereof.

I wish to draw the main conclusion here: Blade consistency – from start to finish – is the primary factor of your shaving comfort.  Consistency is as important as edge sharpness, as we will discuss.  All blades are sharp to varying degrees at one time or another, but not all blades hold their edge well through use.

First, some background is in order. There are 3 factors which affect blade performance:

1. Blade grind.
2. Blade coating.
3. Blade toughness/edge consistency.

Coatings

We will bypass discussion on points of blade grind and material, as they tend to be proprietary per each manufacturer.  Blade coating somewhat less so.

Most blades have a PTFE [Polytetrafluoroethylene, AKA “Teflon”] coating or similar polymer coating, to reduce friction and enhance comfort.  Other coating components can include platinum and/or chrome plating.  PTFE naturally has a low coefficient of friction, so it is very slick to the touch and almost self-lubricating.  However, PTFE tends to be soft and wears out very easily, especially when coated on a slick surface – like that of a polished and ground razor blade – which is then exposed to abrasive materials like your whiskers.

This coating – whatever it is composed of – will usually last for part of your first shave before it is worn away, maybe longer depending on the preparation of the base metal, coating chemistry, and quality of bonding. Thereafter you get down to the “bare metal” of the blade itself.  The cutting-edge will cut before the coating wears off, but as is it wears you will notice the blade changes “feel” as you go through your shave.  This is why your first passes going with the grain [WTG] or across the grain [XTG] will feel different than your finish passes going against the grain [ATG].

For background on how the coating is applied – and how the razor blade is made – please consider viewing a YouTube video:

How Its Made – Double Edge Razor Blades

Sharpness By The Numbers

Now, Let’s examine the sharp evidence before us, Dr. Watson!  Consider this graph:

A more complete list of blade sharpness performance will be found here:

(On a side note, based upon this graph, it appears Gillette owns a majority of the double edge razor blade market.  Especially when you factor in the various brands – Astra, Voskhod, Wilkinson – which are indirectly owned by Gillette. :-/ )

The terms and details in these graphs ought to self-explanatory, but consider your own experiences as you reflect on this:

• Razors blades in the range of 50 [grams of cutting force] will begin to pull and tug, and may require multiple passes – with subsequent irritation – to fully clean up those areas if they clean up at all.
• Blades in the region of low 30’s will be so sharp that you will tend to get irritation, spots and weepers, especially with sensitive skin, when shaving while or directly after showering, hacking away your neckbeard, or shaving against-the-grain finish passes.
• Ultra-sharp blades of any stripe have the unfortunate tendency to “dive into” the skin when doing the finish pass against the grain. This is particularly problematic for men with sensitive skin and/or shaving on the neck, or when shaving later in the week after earlier shaves exfoliate outer layers of skin.
• My experience is you will wish your blade sharpness to dwell right around 40 on the graph or slightly north thereof, for an optimal balance between comfort and efficiency.
• As always, your mileage will vary according to your skin type, shave frequency, shaving prep and materials, razor type, and toughness of your whiskers.

Most of the information in these charts has a U-shaped graph to it, and will demonstrate a sharpness lifecycle as follows:

(Lower “volume” is sharper.)

The exception to this rule includes blades with little or no coating, and/or soft metal, e.g. the Treet Black Beauty or the Shark Super Stainless.  Those blades come to you as sharp as they are going to get, and then get even duller, much like some mothers-in-law.  The much-loved Feather blades are also opposite the above graphic, with an extremely sharp initial cutting edge which gradually wears down with use.

Consider the following examples from the above:

 

These blades all exhibit the trademark characteristics of a thick coating which wears away quickly to expose the sharp cutting edge.  Blades which exhibit these wild swings in sharpness – mild at first but becoming very sharp in use as the coating wears off – will tend to nick more because you will have to change your shave style/pressure slightly to avoid problems with a sharper blade.  Unless you have iron skin, which I sure as heck don’t!  Some folks handle these fine but others with sensitive skin may suffer.

Now examine more consistent blades:

   

These above blade ratings indicate:

• Minimal wear of blade coating – or little blade coating in the first place,
• Good adhesion of coating to base metal surface,
• A decent blade grind which preserves the cutting edge, and/or
• Good blade hardening and tempering of a good quality stainless steel.

Conclusions

As we say in the field of engineering, numbers don’t lie.  Going by the data I’ve compiled in the above graphs, the most consistent blades with the minimal variation in sharpness will tend to be the most comfortable in the long run.

My closing advice to you, dear reader, is invest in razor blades which have the most consistent sharpness using the charts and details above.  Then enjoy the zen-like experience of the smoother, closer and better shave.

Happy shaving!

Charles

Author Profile: Charles Smith is a mechanical design engineer, technical writer and wet shaving enthusiast, frequently suffering from the dreaded Razor Acquisition Disorder and trying to refrain from buying yet another high-end shaving instrument or another few tubs of shave soaps. He resides in northeast Ohio with his wife and 2 cats.