The Facts About Metal Finishing and a Safety Razor
With all the finishes in safety razors, I thought I would write a blog on the subject and talk a little about the different types, costs, benefits, and limitations of different finishes for shavers or safety razors. The subject of surface finishing is a very extensive topic. This article would be too long to talk too in-depth about the subject. My intent is only to provide an overview of the processes so you can understand the topics and maybe ask the right questions. If you want to know more specifics, ping me, I will try to up-date this blog or do a follow-up on the subject in another blog...
I will also talk a little about some other decorative finishes. This subject is also very broad, for some this takes a lifetime to master, especially in high-end watchmaking.
Typically, stainless steel and other metals use a number of different standards to define the finish. The most common standards and measurements are ISO, DIM, ASTM, and Ra to name a few.
https://www.europeanpharmaceuticalreview.com/news/171744/surface-roughness-key-to-microbial-control/
https://isofinishing.com/surface-roughness-in-manufacturing/
The term DIN is an acronym that stands for “Deutsches Institut für Normung” or “German institute for standardization”. ASTM is the US version and stands for American Society for Testing Materials (ASTM). Ra is another acronym for measuring a surface finish used in ISO standards, it stands for “Roughness Average.” Rmax(Distance between lowest valley and highest peak) and numerous other "R" values are also used in ISO standards.
The long and short of these standards is that they attempt to quantify the difference between the “peaks” and “valleys” of a surface. They all have their drawbacks. Often times, manufacturers in and out of the shaving market create their own standards. Measuring a surface finish is very difficult and expensive which leads to a subjective perspective of how smooth or polished a surface is?
For the rest of this article, I will reference the ASTM standard but I will also need to reference “Ra” on occasion as it is the clearest and most well defined for people, however, I will try to reference other industry standards such as “True #8 finish” or “Super #8 finish”.
Here is a chart that shows Ra(Microns) vs the ASTM standard for perspective. In general, the cost to achieve the finish increases as the number ASTM number increases:
* Hairline is another term for a rougher “Brushed” or “Satin” finish. Chart source:
https://www.imoa.info/stainless-solutions/archive/31/Stainless-steel-mechanically-applied-finishes.php
The ASTM standard uses the following grades:
No. 1 and 2 Finish
This finish refers to cold or hot rolled sheet and rod material i.e. pickled (remove scales) hardened, cold, or hot rolled. I should note here that the above material is the surface finish of the blanks we buy to machine our razors parts.
No. 3 Finish
A rough linear texture. Generally a 40-60 grit. There is no standard for a “Machine Finish,” but depending on the part or type of machining it could fall into grade 3. A Ra number might be a better gauge for a machine finish. A turned handle that was machined in a lathe could be classified as having a “Machine Finish,” however some lathes can finish a surface very fine...closer to a No.4 or higher. A mill(used to machine base plates and caps) will generally have a more rougher(#3) finish than a lathe(handle). With a quick polish and no sanding, this finish is also often called a "Pittsburgh polish" producing shiny machine marks.
A bead blasted finish would have a similar Ra to this finish, depending on media used.
No. 4 Finish
Also known as a “Hairline finish” a linear texture but even finer, typically created with a 60-180 grit. Also known as a “Satin”(120 grit) or a “Sanitary”(180 grit) finish.
No. 6 Finish
Also a linear texture but even finer. A soft satin finish...grits 240-320 are used for this finish.
No. 7 Finish
To achieve this surface finish, sanding to a 600 grit and then a 1 step buff is applied. At this level, sanding lines can be easily seen…in other industries this finish is referred to as a “brush mirror” or a “directional mirror” finish.
No. 8 Finish
Highly reflective finish, machine lines removed however the faintest of fine sand lines can be seen. To achieve this finish, sanding continues well above 600 grit...we use +2500 grit paper prior to multiple buffing steps.
Super No. 8 Finish
A “Mirror Finish”! No machine lines, all sanding lines removed. A hip joint implant or a military mirror/lens of some kind would be polished to this level. A diamond compound in excess of 200K grit is used to achieve this finish...
The most polished finish is a Super No. 8 finish, however, this surface finish, often found in the medical, military, and aerospace industry, is especially expensive to produce.
When we were just starting Carbon Shaving Co. I had the opportunity to meet and talk with a local company that polishes optical lenses for missiles in addition to medical devices...diamond paste, under a microscope, while holding the tolerances that are needed is used to accomplish these finishes.
The term "mirror" finish implies a perfect mirror finish on all surfaces, similar to a "Super No 8" finish...I have only seen this on medical implants and military applications and the cost to apply this finish is massive.
High Polish Finish On Carbon Shaving Safety Razors
Now as a designer, we have to grapple with these finishes and decide what is the best finish for a razor application and how best to describe our finish. We refer to our polished finish as a “High Polish Finish.” We use grits and diamond paste higher than 100K grit on some surfaces to achieve a No 8 or higher. We struggle to claim a “No.8” or a “Super No.8” finish on the entire Cx as some of our surfaces have machine lines(under the cap). We still finish these surfaces but keep the machine line in order to preserve the high tolerances of our “pinch design”, we also have some surfaces with a knurling pattern. We choose a “High Polish” finish to describe our Cx models, a common term used in jewelry and the watch making industry because we think it is the best quality for our razors and the best way to describe our finish.
Benefits of a "High Polish" finish include:
Corrosion Resistance
A smooth polished surface provides the best corrosion resistance. Crevices provide a starting point for corrosion to occur. A smooth surface is the most resistant to corrosion.
Easier to Clean
A smooth surface is easier to clean. The crevices on a machined or rough surface finish(High RA) can collect bacteria and germs. This provides more space for them to live and grow, especially in a humid environment.
Less Drag
A polished surface provides a lower drag on a surface (skin), and a polished surface provides a slick surface.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969518/
Sometimes we employ a rough finish when we want the most adhesion. For example, when we are bonding stainless steel or titanium to our carbon fiber, we create a rough surface. We also add knurling to enhance grip on the handle.
Decorative Finishes on a Safety Razor
While the functional element would call for a complete polished surface, we also recognize the desire for the aesthetics to shine through. That leads us to the decorative finishes.
The material we use for our safety razor is of a premium nature, these materials are hard and require more time and effort to finish. Some of these metals include Titanium and the premium stainless steel grades of 316L and 904L, a far more superior quality stainless steel than the “free-machining” grade of 303 stainless steel (I talked about grades and material in an earlier blog post). By using premium metals we believe it gives us the opportunity to do more decorative finishes without compromising the needed corrosive resistance on our Cx razors. Some examples of these decorative finishes include:
Fine/Brushed Finish - Satin Finished Safety Razors
This is a finish we recently added as an option for our titanium Cx-Ti, we polish the surface to a level just shy of a No. 8 finish and then apply a fine brush texture(+2500 grit) to create what we call a "Fine/Brushed" finish. Some of our customers have asked for this type finish as it will hide finger prints and small scratch better then a high polish.
Perlage Finish
Perlage means “pearl” in French. In the high-end watch industry, it is extensively used on the inside of luxury watch cases. This finish is often used in the food and beer industry and can be done using an abrasive and a rotating applicator. We use this pattern to finish under the cap of our 904L stainless steel safety razors. It is done by hand.
“2-Tone” Finish
We occasionally apply a fine etching/bead blasting to non-critical dimensions and surfaces such as the underside of the base plate, caps or the handles. This contrasting surface finish, when shown next to a high polish surface is often used in show car engines. We bring the surfaces to a polished state and then apply a fine etching to darken the metal on select surfaces after masking polished surfaces. We have done limited editions using this finish, the contrast of a polished surface with a finely etched plane provides a striking "2-Tone" contrast.
“Satin” Finish
Technically a satin finish is not specific enough to describe a surface finish. It could be referring to a #3 satin finish(40-60 grit), #4 satin finish(120-180 grit), through #6 satin finish(240-320 grit). A satin finish is generally referred to as a brushed finish due to a paint brush like pattern on the surface similar to the fabric of satin.
Aesthetically a nice finish but not as corrosive resistant as a polished surface yet still easy to clean with its low Ra, that is the reason we currently only offer a brushed finish on our titanium models, which can be best described as a #7 satin finish. Titanium is extremely resistant to corrosion. We could do it with our 316L stainless steel shavers...
A brushed or "true satin" finish takes less time to apply vs a #8 polished finish but also requires skill and practice to execute well. The light scratches that ultimately appear on a razor are less visible on this surface.
Some manufacturers bead blast the surface and call it a "Satin" finish, this is not really an accurate satin finish, ASTM does not have a standard for this finish...a bead blasted surface is rougher, is very inexpensive to accomplish, done in mass, but can hide machine marks(similar Ra to a #3 ASTM).
"Diamond-Like Carbon" or "DLC" coatings - TaC DLC Safety Razor
We use a TaC DLC coating, as it is the slickest of the DLC coatings. This type of DLC is considered the purest form and has similar trates to both diamonds and graphite, both carbon based materials. A thin layer of the element Carbon is added to the surface. Often found in the luxury watch industry but also in the aerospace, performance car racing and other high tech industries. DLC coatings are slicker than a polished surface, approaching that, if not exceeding Teflon, however DLC is significantly harder and more durable then Teflon. The surface is extremely hard. Carbon is the key element in this finish, the surface can be grey to black and is often used on Formula 1 crankshafts to improve wear and fuel efficiency. In the watch industry it is used to prevent scratches and hide fingerprints. This surface finish will not hide or remove surface marks, a high polish finish is required, then a DLC coating is added to produce a smooth, slick surface.
Here we show a TaC/DLC coated custom razor - Damascus-Titanium-Carbon-Fiber-Safety-Razor
Damascus Finish
While not a finish, stainless Damascus has a very unique surface with high and low valleys. Although the true secret of making Damascus steel was lost to time, today the efforts continue with more enhanced and exotic materials including stainless steel damascus. From a Ra perspective, this finish has a high Ra rating and a big "Rmax" measurements. What makes our Damascus unique, is we use a custom forged stainless Damascus made from both 304 and 316 grades stainless steel. We then carefully “etch” the material in acid, the acid attacks or erodes the 304 grade first creating 304 valleys and peaks of 316 revealing the forged Damascus pattern. We then finish the material carefully with numerous grades of grits followed by diamond pastes. We talk more about damascus steel safety razors in this blog.
Other less costly and rougher finishes used in safety razors include:
“Stonewashed” Finish
This finish is created by tumbling a razor with pellets(stones), grit and a solution. Inexpensive, uniform and leaves a non-reflective, rough surface. Similar to a #1 or #2 ASTM finish. This finish can be done in mass, with no hand work, these razor or shavers are generally priced inexpensively.
“Bead Blasted” Finish
Also known as sandblasted, often incorrectly refereed to as a "satin finish", this finish is inexpensive to apply vs any polished or true satin finish, it leaves a rough, uniform finish making the material more susceptible to corrosion, collection of bacteria and will provide more surface drag. Similar to our “2-Tone” finish, however we never use this finish where skin and razor contact. There is no ASTM standard for this finish and its "Ra" can vary depending on the media used (glass beads, porcelain, sand or other. This finish can also be done in mass, with little to no hand work...
“Passivated” Finish
This is a widely used cleaning process for all grades of stainless steel. A citric or other acid is used to remove free iron (iron will rust) from the surface. It can also do a good job of temporarily brightening the surface. This process will leave a very thin protective layer on the surface. It will not lower the Ra or remove machine lines.
“Electropolish” Finish
Electropolishing is a process that makes stainless 30x more corrosion resistant, it also removes some surface imperfection(burs) more effectively...it is similar to passivating but more aggressive in removing free irons from the surface. It can’t be done in a small workshop as it is a very specialized, controlled process, with highly toxic acids. If the metal is electropolished it is also “passivated” however if a metal is “passivated” it is not “electropolished”.
We electropolish some parts prior to final finishing, it is one of the most effective ways to polish threads and knurling.
https://www.ableelectropolishing.com/resources/passivation-vs-electropolishing/
Chrome Plating Finish
On a final note I can’t ignore chrome plating as a surface finish...very inexpensive to make and exceptionally smooth, close to a “Super No. 8” in terms of its smoothness, however, it has 2 major drawbacks that prevent us from using it:
- Durability
The razor will not last. Typically these razors can be mass-produced and are cheap to cast and plate. At the core they are made from a less corrosive-resistant material vs stainless and then covered in a strong but brittle layer of chrome. The problem is, when the razor is inevitably dropped, a crack will start in the brittle chrome material, and corrosion will penetrate this crack in the surface. Another weak point with chrome plating is in the threads which take a lot of wear, this wear causes cracks in the chrome, which will cause the threads to break off. This is where chrome plated razors usually fail...in all fairness they are generally priced low and will last years.
- Toxic
Chrome plating is a very toxic process to the individuals applying the plating and the environment. It is a highly regulated process in the USA and is toxic to the environment. It's one of the big reasons why it is typically done in China, India and 3rd world countries.
You can always tell a chrome plated razor, they all have rounded edges, its difficult(impossible) to chrome a tight edge found in machined safety razors.
Most recently I was shown a chrome-plated razor from a gentleman who had received it from his late father, unfortunately his piece had broken off at the threads...it was sad, as he still kept it. You cannot fix it...
Books are written on the subject of surface finishing but if you have any questions about the finish on a safety razor feel free to reach out here!
Excellent post, Sean!
I learned a lot here; very informative and enlightening.